- Email: [email protected]
Imitating nature: Analogy and experiment in D'Arcy Thompson's Science of Form
Studies in History and Philosophy of Biol & Biomed Sci 78 (2019) 101181
Contents lists available at ScienceDirect
Studies in History and Philosophy of Biol & Biomed Sci journal homepage: www.elsevier.com/locate/shpsc
Imitating nature: Analogy and experiment in D'Arcy Thompson's Science of Form
T
Matthew Holmes Centre for Research in the Arts, Social Sciences and Humanities, Alison Richard Building, 7 West Road, Cambridge, CB3 9DT, UK
A B S T R A C T
D'Arcy Wentworth Thompson's “Science of Form” – the explanation of biological development and morphology through physical forces and mathematical laws – has traditionally been viewed as an idiosyncratic, even heretical, episode in the history of evolutionary biology. Yet recent scholarship has sought to overturn this view by demonstrating that Thompson was active in contemporary scientific networks. This paper argues that a key influence upon Thompson's seminal work, On Growth and Form (1917), may be far more practical, and lie closer to home, than previously realised: experimental demonstrations of basic concepts in physics. Harnessing previously unpublished archival sources, this paper traces Thompson's correspondence with Charles Darling, Arthur Worthington and Cecil Warburton. In these exchanges, Thompson described his own experiments, or requested that experiments be conducted on his behalf. This correspondence, and its subsequent inclusion in the first edition of On Growth and Form, revises our current picture of Thompson from that of an abstract thinker to keen experimentalist. Moreover, his contact with physicists indicates that simple experiments enabled extensive crosstalk between early twentieth century physics and biology.
At the 1894 meeting of the British Association, D'Arcy Wentworth Thompson (1860-1948), Professor of Biology at the University of Dundee, went on the attack against Darwinism. A subsequent account reported that Thompson explained that “the profusion of forms, colours, and other modifications” in the natural world were “due merely to laws of growth” (Anonymous, 1894, p. 435). Thompson also took issue with existing Darwinian explanations for organic forms; for example, that the peculiar shape of the guillemot's egg was an evolutionary adaption for a seabird which nests on the faces of cliffs. The pointed egg of the guillemot had supposedly evolved to roll on its axis when nudged, rather than tumbling into the sea.1 This, thought Thompson, was nonsense. The shape of the guillemot's egg was “merely the natural result of the pressure caused by a relatively large egg passing down a narrow muscular passage” (Anonymous, 1894, p. 435). Thompson (1908, pp. 111-112) would further develop his ideas, arguing that we should first attempt to account for an organic form by recourse to the “simple physical lines with the forces to which it has been subjected.” This maxim would inform Thompson’s (1917) most famous work, On Growth and Form. The first edition of On Growth and Form was a monumental work, designed to persuade its readers that basic physio-chemical forces shaped the organism at every level through extensive use of comparison and analogy. On the smallest scale, he noted that spindle-like structures present during cell division bore a “striking resemblance” to iron filings shaped into lines of force by the poles of a magnet (Thompson, 1917, p.
169). Several orders of magnitude higher and the influence of physical forces on the organism was still apparent. Thompson (1917, p. 682) told his readers the story of how Carl Culmann, a German engineer, had been taken aback when visiting the laboratory of biologist Hermann Meyer. When Culmann spotted Meyer's drawings and specimens of bones, he was astounded to recognise lines of tension and stress identical to those in his engineering projects. These few examples indicate that Thompson's “Science of Form” – the explanation of morphology through physical forces and mathematical laws – was not only an ambitious biological research programme, but also depended upon input from other sciences (Gould, 1971). Yet its relationship to some of the pressing issues of early twentieth-century biology, notably the validity of vitalism, mechanism and organicism, remains ambiguous (Esposito, 2014, p. 91; Maartens, 2017. p. 4202). Thanks in part to his rebuttal of Darwinian explanations, Thompson's Science of Form has sporadically been depicted as an idiosyncratic, even heretical, episode in the history of evolutionary biology.2 Stephen Jay Gould (1971) initially portrayed Thompson as a lone and isolated genius. To his credit, Gould (2002, p. 1183) later backtracked on this interpretation, admitting that he had been “beguiled by D'Arcy Thompson's seemingly anachronistic peculiarities.” More recent scholarship has also sought to overturn this idiosyncratic attraction. Maurizio Esposito (2013; 2014) has argued that Thompson was not an isolated figure, but by the time the second edition of On Growth and Form was published in 1942 was part of a network of like-
E-mail address: [email protected]. An engaging and accessible account of the long-running controversy over the guillemot's egg is given in Birkhead (2016). 2 Some examples include Ridley (1986), Wallace (2006), Whitfield (2006) and Ball (2013). 1
https://doi.org/10.1016/j.shpsc.2019.101181 Received 13 November 2018; Received in revised form 25 April 2019; Accepted 23 June 2019 Available online 28 June 2019 1369-8486/ © 2019 Elsevier Ltd. All rights reserved.
Studies in History and Philosophy of Biol & Biomed Sci 78 (2019) 101181
M. Holmes
manufacture an early fire alarm by inserting a platinum wire into the top of a mercury thermometer. In the event of a fire, the rising mercury would push the wire upward, completing a circuit which would sound an alarm bell. Yet upon his appointment as Lecturer in Science, Darling turned to the study of water droplets and globules. While this subject admittedly did not carry the same practical implications as fire alarm design, it did allow him to unleash his considerable creativity in experimental physics. During a popular lecture series at the City and Guilds Technical College, later published as Liquid Drops and Globules: Their Formation and Movements, Darling (1914, pp. 8-10) examined the shape of detached liquid droplets. He began by smearing a glass plate with grease, to prevent fluid from adhering to it, before adding a series of water droplets to the glass from a pipette. A projector displayed the water drops on a screen for the benefit of his audience, as Darling (1914, pp. 9-10) described his findings: “The larger drops are flattened above and below,” he remarked, “possess rounded sides and resemble a teacake in shape. Those of intermediate size are more globular, but still show signs of flattening; whilst the very small ones, so far as the eye can judge, are spherical.” Darling explained that the shape of the water droplets resting on his glass plate was the result of their size. Despite “the tendency of drops to become spherical,” the “influence of gravitation” was too much for the larger drops to bear, forcing them into an elongated shape (Darling, 1914, p. 10). Only by cancelling out the effects of gravity could one observe perfect spheroids. This feat could be accomplished using floating soap bubbles or suspending oil globules in alcohol (Darling, 1914, pp. 10-11). This demonstration of the shape of water droplets on glass caught the eye of D'Arcy Thompson, then Professor of Biology at the University of Dundee. On February 18th, 1915, Thompson wrote to Darling to compliment his book and its improvements to the experiments of French physicist Felix Plateau. Thompson primarily, however, sought to enlist Darling's help with what he termed a “little biological problem,” of which he was “not mathematician enough to work out.“6 This problem was how to explain the different shapes of sea urchins. “I have a strong idea,” elucidated Thompson in his letter, “that the form of a seaurchin might be explained as an elastic surface deformed by gravity, very much like a drop resting upon a glass plate.“7 He then compared Darling's images of elongated water drops to the shapes of different sea urchins he had observed. Ever the master of understatement, Thompson explained that Darling's book has so enthralled him as “because I am, at this moment, trying to write a little book on the relation of organic forms to the physical forces, a job for which I have plenty of enthusiasm but a sad lack of mathematical skill.“8 This little book was, of course, the gargantuan On Growth and Form. Darling, flattered by Thompson's letter, set to work trying to match the form of sea urchins to his droplets. “With regard to the forms of seaurchins depicted in your card of drawings,” Darling responded in a letter dated February 22nd, “most of them can easily be reproduced in outline by the aid of liquids of approximately equal density to water.“9 Darling had his greatest success replicating the forms of the Coelopleurus genus and Urechinus species of sea urchins, both of which possess an “acute point” and closely resemble a typical water droplet on a flat surface. This form, Darling reported, was “nearly identical in shape with globules I have frequently obtained, in which, on standing, bubbles of gas rose to the summit and pressed the skin upwards without being able to escape.“10 The form of these sea urchins could thus be
minded “romantic” biologists. These included “A. Dalcq, H. Przibram, E. Hatschek, E. Conklin, J. Huxley, F Lillie and, of course, Haldane” (Esposito, 2014, p. 67).3 Yet the question of which scholars and traditions influenced Thompson prior to 1917 and the publication of the first edition of On Growth and Form remains tantalisingly open.4 Far from the Science of Form being an example of isolated, “bluesky thinking,” this paper argues that a formative influence upon Thompson and the first edition of On Growth and Form (1917) was far more practical: experimental demonstrations of basic concepts in physics.5 Harnessing previously unpublished correspondence from the D'Arcy Thompson Collection, this paper examines the exchange of ideas between Thompson and contemporary figures in physics and biology. The use of experiment in this correspondence and subsequent publications raises some intriguing possibilities for our understanding of the Science of Form. First, it confirms that Thompson was never an isolated scholar but was part of a far-reaching scientific network of physicists and naturalists. Second, it confirms that the Science of Form was more reliant on experiment than has been previously recognized. At least some of the key ideas posed in On Growth and Form were based on household experiments and the similarities between inorganic and organic forms produced during these experiments. This paper is divided into three parts. The first examines Thompson's exchange with the London physicist and lecturer Charles Robert Darling. Darling was an authority upon the behaviour of liquid droplets and, encouraged by Thompson, attempted to ascertain whether he could use these to imitate the shapes of various sea urchins. The second part explores Thompson's failed attempt to enlist the aid of Arthur M. Worthington. A physics professor at a Naval College, Worthington shot to scientific acclaim through his work on splashes. Thompson sought, unsuccessfully, to elicit Worthington's aid by comparing the form of splashes with biological structures and giving accounts of his own experiments. The final section of this paper analyses the correspondence between Thompson and Cecil Warburton. Following an exchange with Warburton, a zoologist and Entomologist to the Royal Agricultural Society, Thompson would contact Charles Vernon Boys, author of a popular textbook on experiments with bubbles. What emerges from these interactions is a newfound sense of Thompson as a minor, albeit creative, experimentalist, harnessing everyday objects in his quest to demonstrate how physical forces shaped biological forms. 1. Droplets and sea urchins “A drop of liquid is one of the commonest things in nature,” Charles Robert Darling noted (1914, p. 1), “yet it is also one of the most wonderful.” Darling was a Lecturer in Science at the City and Guilds Technical College in London, an organisation founded in the late nineteenth century to provide a technical education for craftsman and engineers. An itinerant lecturer and industrious author, Darling's wideranging publications reflected the demands of his audience. One of his early publications, on “Industrial Pyrometry,” emerged from a series of lectures delivered to the Royal Society of Arts (Darling, 1911, p. xi). In 1912, while an associate of the Royal College of Science in Dublin, Darling (1912, p. 84) produced a guide to the practical applications of heat for engineers. One passage in the book explained how to 3
Thompson's collaboration with E. Hatschek and Hans Leo Przibram, as described by Esposito (2014), provide valuable evidence for claim that Thompson was strongly influenced by experimental demonstration. Yet for reasons of brevity, this paper restricts itself to the period prior to the publication of the first edition of On Growth and Form (1917). 4 A general overview of Thompson's life and career can be found in a biography by his daughter, Ruth D'Arcy Thompson (1958). 5 A similar turn towards the practical and everyday has occurred in the historiography of Mendelism and early genetics, which now looks increasingly towards agriculture. See Gliboff (2015).
6 All archival sources cited in this paper are located in the Special Collections of the University of St Andrews Library. The Call Number (MS) is given for ease of access. MS 19100. 7 MS 19100. 8 MS 19100. 9 MS 19102. 10 MS 19102.
2
Studies in History and Philosophy of Biol & Biomed Sci 78 (2019) 101181
M. Holmes
explained, a sea urchin was essentially “a spherical shell symmetrically depressed under the influence of gravity.” Thompson (1917, p. 664) also referred to his correspondence with Darling, whom he characterised as “an acknowledged expert in drops,” at length. He described how Darling had attempted to recreate the shape of sea urchins using drops and had only run into difficulty with the troublesome Asthenosoma and its lantern. Thompson (1917, p. 664) also described the analogy between bubbles of gas in Darling's drops and ova in sea urchins. On Growth and Form ultimately included two citations from Darling's first letter of February 22nd: the first on the ease of reproducing the form of sea urchins using drops and the second describing how bubbles of gas could push drops into a conical shape reminiscent of the Coelopleurus and Urechinus urchins (Thompson, 1917, pp. 663-664). Thompson's correspondence with Darling, and its later inclusion in On Growth and Form, is striking for several reasons. The first is that a sophisticated and convincing case study in Thompson's Science of Form was derived from popular, even elementary, physics. Darling, a travelling lecturer based at a technical institution, was far from a prestigious figure in the scientific community. His experiments, comprising of droplets of water and dripping syrup, possessed a distinctly homemade feel. Almost as striking as the simplicity of Darling's experiments was his lack of mathematics. Thompson had complained of his own lack of mathematical skill when he had first written to Darling on February 18th. Yet Darling showed no inclination to provide Thompson with his desired mathematical explanation of the form of sea urchins. In fact, the physicist was dismissive of the idea. “So far,” wrote Darling, “I have received little assistance from the mathematical side of the subject.“18 Most mathematical work on surface tension had apparently been devoted to the skins of globules, rather than explaining the stability of unusual shapes such as liquid columns (Darling, 1914, p. 43). “How far mathematical investigations would assist the discovery of phenomena of this kind it is impossible to say,” Darling informed Thompson, “but certainly a great deal can be done without it. The variety of forms obtainable is almost endless.“19 The case of the sea urchin tells us that Thompson was not merely content with observing that organic and inorganic forms were shaped by the same physical forces. He was also prepared to directly compare aspects of the material world with that of the biological. For Thompson, a lack of any mathematical understanding of the form of droplets and sea urchins was an unfortunate downside of this comparison. Yet far from being a purely theoretical or mathematical thinker, Thompson was more than willing to collaborate with a practically-minded physicist on simple experiments. The sea urchin also leads to what is in part a historian's caveat, in part a reason for admiration. We have just examined how Darling's lectures and experiments interacted with Thompson's Science of Form. Yet the sea urchin was only allocated some five pages of the 1917 edition of On Growth and Form (Thompson, 1917, pp. 661-665). In part, this outcome reflects the sheer investment and resources Thompson poured into his book. Yet it also indicates that we should remain cautious before drawing any firm conclusions about the significance accorded to elementary physics experiments in the Science of Form. In the remainder of this paper, we shall examine some further instances of Thompson's engagement with household experiments, which reveal that he was not only intrigued by such experiments, but quite capable of carrying out his own.
explained as a contest between gravity and these rising bubbles. Gravity distorted the sea urchin into an elongated shape, while bubbles under its elastic surface pushed the top of the sea urchin upwards to form their points. Yet there was one sea urchin whose form, explained Darling, continued to elude him: “The Asthenosoma appears the most difficult, as although I can reproduce either half easily, it may prove difficult to get the two together. As soon as possible I will get the camera to work, and let you see the results.“11 Darling's experiments reinforced Thompson's faith in his interpretation of the form of sea urchins. Only two days after Darling's response, Thompson fired off another letter to address “what you [Darling] say about the urchins with an acute point as being comparable to globules that contain gas bubbles, I had already thought of the same idea, though not quite in the same way.” Thompson pointed out that sea urchins contain “large masses of ova and these are laden with oil.” These ova, explained Thompson, were “concentrated towards the apex [of the sea urchin] and this is just the condition which occurred to me as accounting for the vertically elongated and pointed conformation of the shell.12 The sea urchin was then, at its most basic level, a liquid droplet held in an elastic film. It was flattened toward the sea floor by gravity but rose to a central point thanks to its oil-coated ova. Thompson also provided an apologetic explanation for the troublesome Asthenosoma, which he confessed he should not have included in his set of drawings. “The form [of the Asthenosoma],” he explained, “is complicated by the large solid mass of the “Aristotle's lantern” [the sea urchin's mouthpiece] inside the flexible, membraneous shell.“13 The presence of the Aristotle's lantern altered the shape of the sea urchin in a manner which Darling could not have replicated with liquid droplets alone. With the sea urchin conundrum effectively solved, Thompson now turned to the form of the lagena genus of the foraminifera: tiny, singlecelled marine organisms, possessing a shell and thread-like ectoplasmic strands. In his Liquid Drops and Globules, Darling (1914, pp. 7-8) had used syrup to demonstrate how liquids droplets attempted to keep a spherical shape. By watching syrup drip off a glass rod, Darling (1914, p. 7) claimed to have witnessed “a remarkable property of a liquid surface,” its “tendency, as in the case with all stretched membranes … to reduce the area of [its] surface to a minimum.” Although this tendency, at least in the case of syrup, would be overwhelmed by the force of gravity, once a droplet of syrup fell it would immediately assume its spherical shape once more (Darling, 1914, p. 8). This experiment came as encouraging news to Thompson, who in his letter of February 24th wrote that “I have long had an idea that the little foraminiferal shells called lagena were formed as so many hanging drops, but the difficulty was to find evidence that they really hang.“14 Thompson noted that cross-sections of the nodosaria genus revealed “the necks of the little bottle-shaped lagenae fitting one into another.“15 Perhaps these shells upon shells had been formed by hanging drops, as “the first-formed lagena accumulating a new drop of protoplasm and within as it were falling so far through the new drop while the whole system hung by the contact between this latter and the surface water-film.“16 Sadly for this latest theory, a brief reply by Darling on the 27th February informed Thompson that further research on the matter would be required.17 What impact then, did this exchange have on the published version of On Growth and Form? Thompson (1917, p. 662) once again relayed his vision of the sea urchin as the product of an “equilibrium of forces.” Just like a drop of water on a plate, Thompson (1917, p. 663)
2. Splashes and hydroids 11
MS MS 13 MS 14 MS 15 MS 16 MS 17 MS 12
“The splash of a drop is a transaction which is accomplished in the twinkling of an eye,” Arthur M. Worthington acknowledged (1895, p. 7) during his 1894 lecture at the Royal Institution, “and it may seem to
19102. 19101. 19101. 19101. 19101. 19101. 19102.
18 19
3
MS 19102. MS 19102.
Studies in History and Philosophy of Biol & Biomed Sci 78 (2019) 101181
M. Holmes
Worthington's work primarily stemmed from two areas of interest: “(1) the regular and beautiful notching of the little cups or calycles of certain zoophytes and (2) the appearance of a beautiful and regular pattern of ridges and furrows upon the shells of certain Foraminifera (Lagenae).“22 Thompson's theorising on the shape of Lagenae shells had met a dead end with Darling some several months earlier. Undeterred, Thompson repeated his assertion that the form of their shells resembled “hanging drop” to Worthington.23 Thompson also attached “two or three pages” of his draft manuscript regarding calycles to the letter, “That you might better understand the lines on which I am going.“24 Thus far, Thompson's typed letter was typical of the many he dispatched over the course of 1915: highly complimentary and inquiring into one or two biological phenomena he felt were most amenable to the insight of physicists. Yet toward its conclusion, the tone of his letter to Worthington changed. “While I have this opportunity of writing to you,” recalled Thompson, “I am reminded of a little experiment that I made many years ago and thought no more of.“25 He went on to describe a curious formation he had once found in his local brickfields. These formations consisted of “(1) of a quoit-like ring of hardened clay and (2) of a very smooth and regular oblate spheroid of the same material, resting upon the former.“26 Although geologists were reportedly baffled, Thompson thought that these spheroids and their rings had been formed by splashes. He reported that he “was able to imitate them very closely by splashing drops of water onto a dish of fine sand.“27 These splashes wet the sand, causing it to draw together and create a spheroid. The water then drained from the spheroid, wetting the surrounding sand to create a concentric ring. “I tried a few other experiments with such substances as plaster of Paris,” recalled Thompson, “with considerable success.“28 In a 1916 letter to the mathematician George Greenhill, Thompson complained that his appeal to Worthington had gone unanswered: “[I] not want to think evil of him, but in my last [letter] I besought him for a postcard."29 Yet this setback did not prevent Thompson from further pursuing the link between splashes and animal forms, nor from drawing upon Worthington's studies in the first edition of On Growth and Form (1917). Chapter Five of On Growth and Form takes the reader through the theories of Plateau and goes into great detail describing his experiments on the separation of a liquid cylinder into droplets (Thompson, 1917, pp. 227-229). The competition between the outward pressure of a liquid and the inward pressure of its surface tension could, according to Thompson (1917, pp. 235-236), explain a huge range of phenomena. Following in Worthington's footsteps, Thompson (1917, p. 236) described the notched edges of a wave approaching a shore as a consequence of surface tension being overwhelmed. The shape of splashes could also be explained using Plateau. “In some of Mr. Worthington's most beautiful experiments on splashes,” explained Thompson (1917, pp. 235-236), “it was found that the fall of a round pebble into water from a considerable height, caused the rise of a filmy sheet of water in the form of a cup or cylinder; and the edges of this cylindrical film tended to be cut up into alternate lobes and notches.” The shape of a splash reminded Thompson (1917, p. 236) “of the beautifully symmetrical notching on the calycles of many hydroids, which little cups before they became stiff and rigid had begun their existence as liquid or semi-liquid films.” The liquid-like film which formed the distinctive cup of young hydroids, tiny ocean-dwelling animals, was naturally unstable. This instability led to segmentation,
some that a man who proposes to discourse on the matter for an hour has lost all sense of proportion.” Worthington, Headmaster and Professor of Physics at the Royal Naval Engineering College in Davenport, of course spent his lecture attempting to undermine this proposition. Worthington (1895, pp. 8-9) had long been fascinated by splashes, ever since when a schoolboy at Rugby he had accidentally dripped ink onto some smoked glasses and reported the formation of fine concentric rings to the Rugby Natural History Society. Worthington (1895) had first attempted to capture the shape of splashes using flashes of light and the naked eye, before moving onto new photographic technology.20 The final result of Worthington's efforts to describe and capture the splash of water droplets was an acclaimed monograph, A Study of Splashes, published in 1908. As if to affirm both his military credentials and the practical applications of his chosen science, the first photograph in the book was that of the metallic “splash” created when a projectile penetrated an armoured plate (Worthington, 1908, p. iv). Worthington (1908, p. 1) began his study by noting that many of his readers, caught in a shower of rain, may have watched “half-subconsciously, the thousand little crystal fountains that start up from a surface of pool or river; noting now and then a surrounding coronet of lesser jets, or here and there a bubble that floats for a moment and then vanishes.” Yet despite the ubiquity and our everyday experience of falling drops, the sequence of the splash, which occurs “within the limits of a few hundredths of a second … taxes the highest mathematical powers to elucidate” (Worthington, 1908, pp. 1-2). Surface tension was key to understanding the shape of drops and their behaviour once they hit a solid or liquid surface. “The first principle to be understood,” explained Worthington (1908, p. 32), “is that the surface layers of any liquid behave like a uniformly stretched skin or membrane, which is always endeavouring to contract and to diminish its area.” Hanging drops existed, at least temporarily, thanks to this principle. Worthington (1908, p. 33) described how the stretched skin on a hanging drop pressed back upon its contents, preventing the liquid from simply flowing away. Darling (1914, p. 7) would reiterate the same argument in his own book some six years later. Worthington (1908, p. 36) also expanded upon the demonstration first performed by the “blind Belgian philosopher Plateau,” that a cylinder of liquid could not remain “of stable equilibrium if its length exceeds about 3 1/7 times its diameter.” Once beyond this ratio, the inward pressure of surface tension would overwhelm the outward pressure of the liquid and the cylinder would split into drops. This transition from stable equilibrium to instability and segmentation could be readily observed in nature. Worthington (1908, p. 39) explained how waves approaching a beach initially have a “smooth, horizontal cylindrical edge,” from which “at a given instance, are shot out an immense array of little jets which speedily break into foam, and at the same moment the back of the wave, hitherto smooth, is seen to be furrowed or combed.” These jets and furrows occurred thanks to the same laws Plateau had proposed to explain the segmentation of liquid columns. The power of surface tension to shape nature could also be seen in “the dimples made by the weight of an aquatic insect, where its feet rest on the surface without penetrating it” (Worthington, 1908, p. 35). Fresh from his exchange with Darling, Thompson wrote to Worthington on November 24th, 1915, ostensibly to ask for his permission to reproduce some figures from A Study of Splashes. Yet Thompson, as ever, was also interested in a physicist's take on his forthcoming book, On Growth and Form, which he explained to Worthington as “an attempt to bring elementary physics and elementary mathematics to bear upon the great variety of matters connected with organic morphology.“21 Thompson stated that his allusions to
22
MS MS 24 MS 25 MS 26 MS 27 MS 28 MS 29 MS 23
20 Worthington is familiar to historians and philosophers of science through the work of Lorraine Daston and Peter Galison (2007) on objectivity. 21 MS 29564.
4
29564. 29564. 29564. 29564. 29564. 29564. 29564. 28662.
Studies in History and Philosophy of Biol & Biomed Sci 78 (2019) 101181
M. Holmes
which appeared in the formation of ridges, furrows and notches. “In the case of the hydroid calycle,” wrote Thompson (1917, p. 237), “we are led to the conclusion that the two common and conspicuous features of notching or indentation of the cup, and of constriction or annulation of the long cylindrical stem, are phenomena of the same order and are due to surface tension, in both cases alike.” Thompson, in essence, saw the cups of hydroids as analogous to a splash. The ridges on their cups and the notches at their edge spoke of the same physical forces which created Worthington's carefully captured splashes. Similarly, Thompson viewed hydroids' long stems as a Plateau's cylinder in the process of segmentation. As the hydroid matured and its cup and stem hardened, these morphological manifestations of liquid instability were forever frozen upon its surface. What role, then, did Thompson's own experiments play in this episode? Even with the aid of photography, liquid splashes were quick and difficult to study. Yet, noted Thompson (1917, p. 238), “we can repeat and demonstrate many of the simpler phenomena, in a permanent or quasi-permanent form, by splashing water on to a surface of dry sand, or by firing a bullet into a soft metal target.” On one level, Thompson's experiments with sand and plaster of Paris were a means of capturing the splash for study in such a permanent form. Yet these experiments also proved to serve another point. “There is nothing,” argued Thompson (1917, p. 238), “to prevent a slow and lasting manifestation, in a viscous medium such as a protoplasmic organism, of phenomena which appear and disappear with prodigious rapidity in a more mobile liquid.” A parallel had once again been drawn between the organic and the inorganic. The legacy of the physical forces which shape waves and splashes could be found in brickfields, in a dish of sand or on a hydroid. Glassmaking and pottery provided analogies of how an equilibrium of forces could create a simple form. Yet Thompson (1917, p. 239) complained that “we are for the present on the uncertain ground of suggestion and conjecture.” Even the simplest of organic forms, including sea urchins and hydroids, could not yet be described in mathematical terms. Although Thompson never managed to engage Worthington with his Science of Form as he did Darling, his attempt to do so is nonetheless instructive. Again we can see that Thompson was fascinated by simple experiments and willing to reach out to physicists outside the university. He was also prepared to draw close parallels between inorganic and organic forms. Geological formations could be replicated through experiment. In turn these experiments revealed the fundamental forces of nature, which shaped organic forms. Both hydroids and the brickfield formations were analogous to a drop of water in a dish of sand. Yet on this occasion Thompson did not outsource experimental work, as he had with Darling and his queries into the form of sea urchins. Thompson had carried out basic experiments of his own accord and attempted to engage Worthington with his findings. Had he been successful in soliciting Worthington's interest, his sand experiments may well have played a more significant role in On Growth and Form than they did (Thompson, 1917, p. 238). In lieu of a developed experimental programme, Thompson instead relied upon the authority of Worthington and analogies with industrial techniques to make his case for the form of the hydroid.
was to sit on a committee charged with ridding the ceiling of Westminster Hall of an infestation of Death Watch beetles (Clark, 2009, p. 214). When his services were not demanded by Parliament, Worthington explored the lives of spiders, mites and ticks. The former, however, were his greatest passion (Tate, 1958, p. 1771). Warburton (1890, p. 29) soon established a name for himself in arachnology with a paper on the spinning glands of spiders. A chapter in The Cambridge Natural History, to which Thompson was also a contributor, further cemented Warburton's reputation as a premier arachnologist. In his lengthy treatment of spiders, Warburton (1909, p. 343) discussed how some spiders wove circular webs of “parallel silken lines … varying in number according to the special purpose for which they are designed, and sometimes adhering more or less to one another on account of their viscidity and closeness.” Yet Warburton was not content to merely observe webs in the field. After all, one could quite easily “carry off a newly-constructed web – or, better still, one not quite finished – on a piece of plate glass, to which it will adhere by reason of the viscid spiral, and on which it may be examined at leisure” (Warburton, 1909, p. 347). Once arranged on the glass, a staining fluid could be added to the web, revealing its hidden structure. “It will appear to consist,” reported Warburton (1909, p. 347), “of a thread strung with beads of two sizes, occurring with pretty uniform alternation, though two of the larger beads are often separated by two or more of the smaller.” This phenomenon, noted Warburton (1909, p. 348), was a consequence of the “viscid matter” on the thread arranging itself into the beads. At an 1889 lecture at the Royal Institution, the physicist Charles Vernon Boys had declared that he had been able to replicate the formation of these beads in quartz fibres. “A liquid cylinder, as Plateau has so beautifully shown,” Boys (1889, pp. 249-250) reminded his audience, “is in an unstable form.” Just as such a cylinder would break up into separate droplets, so a cylinder or thread of liquid quartz would “break up into spheres” (Boys, 1889, p. 250). As the quartz cooled into a solid, the spheres would disappear: “thus completely agreeing with the results of Plateau's investigations” (Boys, 1889, p. 250). Boys was even able to replicate the sticky liquid which spiders coated on their webs to catch flies. By coating a quartz fibre with castor oil, Boys (1889, p. 250) observed the emergence of “beaded threads,” which made his fibres appear “quite indistinguishable from a real spider web and … just as good at catching flies.” The following year, at the meeting of the British Association in Leeds, Boys blurred the boundaries between the organic and inorganic still further. His quartz fibres were identical in appearance to the thread of a spider's web, leading him to the question of “what a spider would do if by any chance she should find herself on such a [quartz] web” (Boys, 1890, p. 606). In front of a live audience, Boys (1890, p. 606) set about trying to transfer three small spiders from their own webs onto his quartz replicas. His demonstration did not go entirely to plan: “Unfortunately this spider has slipped and has got away,” Boys (1890, p. 250) informed onlookers, “but with another I am more successful.” His plan had been to show how the spiders would struggle to climb the smooth quartz fibres without the presence of liquid spheres. Yet the particularly stubborn spider was able to climb the quartz (Boys, 1890, p. 250). Despite such difficulties, Warburton (1909, p. 348) was convinced that Boys was correct. The formation of liquid beads on a spider's web was a purely mechanical process. In addition to manhandling uncooperative spiders in front of the British Association, Boys was also an educationalist. Over the winter of 1889–1890 he delivered a lecture course at the London Institution to a young audience. The lectures, later published by the Society for Promoting Christian Knowledge as Soap-Bubbles and the Forces Which Mould Them, began with what is now a familiar trope. “I do not suppose that there is any one in this room who has not occasionally blown a common soap-bubble,” ventured Boys, “and while admiring the perfection of its form, the brilliancy of its colours, wondered how it is that such a magnificent object can be so easily produced” (Boys, 1896, p. 9).
3. Globules and spiders’ webs The life of a budding naturalist is sometimes a tense one. “The 75 spp. [multiple species] of exotic spiders arrived safely,” reported a young Cecil Warburton to D'Arcy Thompson in 1899, although “The spirit had about all left the tubes, but luckily I was able to fill them up before they dried.“30 A Cambridge zoology graduate, Warburton had succeeded the esteemed Eleanor Ormerod as Consultant Entomologist to the Royal Agricultural Society in 1892. One of his newfound duties 30
MS 22768. 5
Studies in History and Philosophy of Biol & Biomed Sci 78 (2019) 101181
M. Holmes
the wire, the varnish would divide into globules. Having interrogated Warburton on the viscid globule, Thompson moved to contact Boys. Yet their exchange, according to surviving letters, did not begin until 1920. By this time, On Growth and Form had finally been delivered to Cambridge University Press and published, to great acclaim. On June 19th, 1920, Boys – responding to a missing letter of Thompson's – wrote with instructions on how to produce a light spectrum using an arc lamp.39 It was only in a later letter, written on October 28th, 1921, that Boys finally discussed bubbles with Thompson. Boys confessed that he could “do nothing” to help Thompson with his inquiries. Over the years he had lost or mislaid much of his material on the subject and had “never seen them since or blown a bubble.“40 Boys did, however, direct Thompson to his textbook. “So follow the directions at the end of my book very diligently,” wrote Boys, jokingly adding “with piety,” and directed Thompson to other authors.41 By this time, Boys (1920, pp. 188-190) was probably referring to an updated edition of his textbook, which discussed the use of electricity to merge bubbles in its end pages. This one-sided exchange indicates that Thompson was belatedly interested in Boys' work on bubbles and was attempting to replicate his experiments. Although Thompson's attempted experiments with bubbles came too late for inclusion in the first edition of On Growth and Form, spiders' webs and their globules did appear in the book. “In the spider's web,” wrote Thompson (1917, p. 231-232), we find exemplified several of the principles of surface tension which we have now explained.” Thompson (1917, p. 232) described how spiders secreted two forms of viscous fluid when constructing their webs. The first issued from the body as a semi-fluid, drying upon exposure to air. The second secretion maintained its fluid form for several hours, coating the web as a liquid cylinder. During this drying period, a slow-motion demonstration of Plateau's limit to the length of liquid cylinders could be observed. Thompson (1917, p. 232) explained that this cylinder “disrupts in the usual manner, passing first into the wavy outline of an unduloid, whose swollen portions swell more and more till the contracted parts break asunder.” By the time this process was complete, “a series of spherical drops or beads, of equal size [were] strung at equal intervals along the thread.” To further illustrate his account, Thompson (1917, p. 232) referred to the household experiment he discussed in conversation with Warburton: “If we try to spread varnish over a thin stretched wire, we produce automatically the same identical result.” Once again, Thompson's engagement with Warburton – and more indirectly Boys – demonstrates that he was able to reach out to a larger scientific network whilst constructing his Science of Form. This network consisted of naturalists and physicists, both of whom could be engaged with basic experiments and analogies. The story of the spiders' webs also demonstrates that Thompson was not alone in this ambition. Boys and his quartz webs at the British Association in 1889 represent perhaps one of the most blatant attempts to blur the boundaries between the organic and inorganic. Miall followed in Boys' footsteps with his Royal Institution lecture on aquatic organisms and surface tension in 1892. By the time that Thompson began to reach out to various scientists during the writing of On Growth and Form, there existed a receptive audience for his ideas. Mirroring his attempted interaction with Worthington, Thompson was again able to reach into his past to bring a basic experiment to bear on biological questions: this time the application of varnish onto a stretched wire. This experiment was, at least to Warburton, a novel one. Yet the case of Boys and Miall suggests that the days when biologists would be filled with “great wonder and admiration” by phenomena created through physical forces were numbered
To demonstrate how the elastic skin of bubbles was created by surface tension, Boys (1896, pp. 19-20) deployed a common piece of apparatus known as Van der Mensbrugghe's float. Consisting of a cork attached to a wire framework, the entire apparatus was forcibly submerged by Boys. As the cork attempted to rise, its wire frame pressed against the surface of the water with enough force to keep it submerged. Intriguingly, this same experiment was repeated at the Royal Institution on March 4th, 1892 by Louis Compton Miall (1842-1921), the first Professor of Biology at the University of Leeds. “It is necessary to the exposition of my subject,” declared Miall, “that I should begin by reminding you of some well-known properties of the surface of water … familiar to every student of physics.” (Miall, 1892, p. 7). Miall then proceeded to carry out a series of basic experiments, including Mensbrugghe's float. He used these demonstrations to argue that surface tension was a pervasive physical force which shaped the life of aquatic organisms. In what was perhaps a missed opportunity for both, Thompson and Miall's correspondence only reveals that they discussed matters of health and staff appointments at Leeds.31 Nor did Thompson initially seek to contact Boys over his work with bubbles or quartz rods. He instead, some fifteen years after his first exchange with the young naturalist, sought out Warburton's opinion on the formation of globules. Thompson contacted Warburton on February 9th, 1915 to request “any information regarding the variations in different species of the spider, of the form, size and number of the viscid globules on the web.“32 Referring to Warburton's piece in The Cambridge Natural History, Thompson also noted that “you [Warburton] credit Boys with discovery that these beads are formed automatically by surface tension … [yet] with all respect to Boys it was known to many long before his day.“33 Thompson recalled how, while studying physics at Cambridge during the 1870s, it was “a standing joke of Yate's part to laugh at the biologists who were innocent, and ignorant enough to think otherwise.“34 The jibe was presumably directed at those biologists who had no explanation for how these beads were created. The classic A History of the Spiders of Great Britain and Ireland by John Blackwall (1861, p. 10), for instance, estimated the number of these beads or globules on a typical web – somewhere in the region of 120,000 – but did not explain how they came to be. On February 16th Thompson wrote to Warburton once more. “Granting the physical hypothesis” of droplet formation on webs, mused Thompson, meant that such details “as the size and distance apart of the globules, must depend upon such variables as the thickness of the thread, the thickness of the superimposed viscid layer” and so on.35 Thompson requested new information from Warburton. He asked how the arrangement of globules on the web differed between spiders and if these differences “corresponded to the various differences which are theoretically possible.“36 Thompson also asked whether these differences could be correlated with “controlling factors,” such as the ratio of thread thickness to that of the liquid cylinders which coat it.37 Thompson did agree with Warburton that it was Plateau who had first hit upon the idea of the limits to stability in a liquid cylinder or column. Boys and his quartz fibres had demonstrated the applicability of Plateau's law on a microscopic scale. Yet a far simpler demonstration could be carried out in a domestic setting. Thompson described how “you could illustrate it every bit as well by tying a piece of thin copper wire (“binding” wire) to the door-knob, holding it tight and doing your best to brush over it a smooth coat of black varnish.“38 Instead of covering 31
See MS 22229 to 22233 for Miall and Thompson's Correspondence. MS 22771. 33 MS 22771. 34 MS 22771. 35 MS 22772. 36 MS 22772. 37 MS 22772. 38 MS 22772. Thompson also explained that he had encountered Plateau's work, including the latter's papers between 1843 and 1868, and Plateau's 1873 32
(footnote continued) book. 39 MS 11244. 40 MS 11245. 41 MS 11245. 6
Studies in History and Philosophy of Biol & Biomed Sci 78 (2019) 101181
M. Holmes
multiple offerings.” Is the experimental side of Thompson simply one of these highly selective perspectives? The wider correspondence discussed in this paper suggests that this is not the case. Thompson's letters to Worthington and Warburton demonstrate that experiment had long been an important part of his methodology and training. Far from being a throwaway line inserted into On Growth and Form, the use of experiment to draw analogies between the organic and inorganic was an important part of the Science of Form. The occasional reference to experiment in the published versions of On Growth and Form downplay the effort and thought Thompson and his collaborators put into their experimental programmes. Thompson's use of experiment also bears upon his wider use of mathematics. Contrary to what we might expect, On Growth and Form contains surprisingly few “actual equations, or even numbers,” instead relying upon “the laboratory manipulation of liquid drops, columns, solutions … contrived to mimic organic forms” (Keller, 2002, p. 65). Thompson's exchange with Darling in February of 1915 shows that Thompson was keen to establish a mathematical account of the different forms taken by sea urchins. Yet Darling was unable or unwilling to do so. The experimental recreation of sea urchins by Darling was therefore a substitute, or at least a first step, for a mathematics that did not yet exist. The lack of mathematics in the Science of Form was not necessarily due to lack of drive or ability on the part of Thompson. Keller (2002, p. 67) has argued that “Thompson's particular blend of diverse metaphysical traditions may have been idiosyncratic, but the component strands upon which he drew were well-established cultural resources.” One of these cultural resources was the experimental physics demonstrated in technical colleges, public lectures and households across Britain. Thompson was an experimentalist among many other experimentalists: a quality which might have made the first edition of On Growth and Form all the more appealing to his contemporaries.
(Thompson, 1917, p. 234). 4. Conclusion: D'Arcy Thompson the experimentalist? By tracing D'Arcy Thompson's use of experiments in On Growth and Form, this paper supports a growing sense of scepticism towards declarations of Thompson's isolation or idiosyncrasy. His pre-1917 correspondence suggests that Thompson was never entirely separated from a wider intellectual context. Just as Esposito (2013; 2014) places a latecareer Thompson within a European network of romantic biologists, so this paper places him within an experimentally-minded community. This community consisted of both fellow biologists like Warburton, and practically-minded physicists based at technical colleges. Thompson's exchange with Darling and attempted engagement with Worthington point to a new image of Thompson as a budding experimentalist. He suggested that Darling attempt to replicate the form of sea urchins through experiment and conducted his own with such commonplace items as varnish, copper wire and dishes of sand. As his successor in Dundee, Alexander Peacock, recalled: “Fortunate were all who saw him use sketches, bits of paper and string, and soap bubbles to explain the mathematics of the honeycomb, the nautilus shell and such like recondite things” (Jarron, 2013, p. 2). Why then, was Thompson so willing to use experiment to recreate natural forms, or demonstrate the applicability of physical forces to biological phenomena? The opening chapter to On Growth and Form provides one answer. Through correlation and equation, Thompson (1917, p. 6) argued, “the quest for physical causes merges with another great Aristotelian theme, – the search for relations between things apparently disconnected.” This refers to the Aristotelian philosophy of similitude. “Newton,” recounted Thompson, “did not shew the cause of the apple falling, but he shewed a similitude between the apple and stars.” In other words, Newton did not give an exact account of what gravity was. He did, however, show that the same physical force which causes apples to fall also causes stars to attract other celestial bodies and move in orbits. Similarly, the experiments conducted by or on behalf of Thompson showed how physical forces governed both organic and inorganic forms alike. Hence sea urchins were comparable to droplets, or splashes to hydroids. “The search for differences or essential contrasts between the phenomena of organic or inorganic, of animate and inanimate things has occupied many men's minds,” noted Thompson (1917, p. 7), “while the search for community of principles, or essential similitudes, has been followed by few.” According to Thompson's principles, basic physics experiments were not only a valid avenue of research but were integral to the Science of Form. Thompson, like many of his contemporaries, sensed that explaining the appearance of organic forms through appeals to evolutionary history was highly speculative (Esposito, 2014, p. 82). The Science of Form therefore rejected Darwinian explanations in favour of a system of forces acting upon the growing organism (Esposito, 2014, pp. 101-102). In the light of this context, the tabletop experiments conducted by Thompson and his collaborators must have held great appeal. Backed by the philosophy of similitude, it made sense that seemingly mundane objects and phenomena, such as droplets, splashes, sand and wire, operated under the same physical laws as those which shaped organic forms. Yet divorced from the complexity of biology, the workings of these laws could now be seen with greater clarity. Perhaps of even greater importance was that experiments recreated the conditions which shaped organisms for first-hand observation in real time. The contrast with the distinct and speculative nature of Darwinian explanations could not have been clearer. So how does a newfound perspective of Thompson as experimentally-minded and in pursuit of similitudes add to our current understanding of the Science of Form? Evelyn Fox Keller (2002, p. 62) states that one of the problems with working with On Growth and Form is simply that it is “a very large book, composed of many different parts, [and] it has been possible for readers to quite selectively draw from its
Acknowledgements My thanks go to the Special Collections staff at the University of St Andrew's Library, who were generous with their time and hospitality. I would also like to thank the organisers and attendees of the October 2018 History of Science, Technology and Medicine Network Ireland Annual Conference in Belfast, where I presented an early version of this paper. I owe a special debt of gratitude to the members of the History and Philosophy of Biology reading group at the University of Leeds, who first introduced me to the world of D'Arcy Thompson. Finally, I am grateful to two anonymous referees for their welcome feedback and suggestions. References Archival Sources D'Arcy Wentworth Thompson letters, archives of the Special Collections of the University of St Andrews Library.
Published Sources Anonymous (1894). Biology at the British association. Nature, 50(1296), 433–436. Ball, P. (2013). In retrospect: On growth and form. Nature, 494(7435), 32–33. Birkhead, T. (2016). The most perfect thing: Inside (and outside) a bird's egg. London: Bloomsbury. Blackwall, J. (1861). A history of the spiders of Great Britain and Ireland. London: Robert Hardwicke. Boys, C. V. (1889). Quartz fibres. Nature, 40(1028), 247–251. Boys, C. V. (1896). Soap-bubbles and the forces which mould them. London: Society for Promoting Christian Knowledge. Boys, C. V. (1890). Quartz fibres. Nature, 42, 604–608. Boys, C. V. (1920). Soap-bubbles and the forces which mould them. London: Society for Promoting Christian Knowledge. Clark, J. F. M. (2009). Bugs and the victorians. New Haven: Yale University Press. Darling, C. R. (1911). Pyrometry: A practical treatise on the measurement of high temperatures. London & New York: Spon & Chamberlain. Darling, C. R. (1912). Heat for engineers: A treatise on heat with special regard to its practical
7
Studies in History and Philosophy of Biol & Biomed Sci 78 (2019) 101181
M. Holmes
Witkowski, & W. Christopher (Eds.). A history of embryology (pp. 35–67). Cambridge: Cambridge University Press. Tate, P. (1958). Mr. Cecil Warburton. Nature, 182(4652), 1771. Thompson, D. W. (1908). On the shape of eggs, and the causes which determine them. Nature, 78(2014), 111–113. Thompson, D. W. (1917). On growth and form. Cambridge: Cambridge University Press. Thompson, R. D. (1958). D'Arcy Wentworth Thompson: The scholar-naturalist. Oxford: Oxford University Press. Wallace, A. (2006). D'Arcy Thompson and the theory of transformations. Nature Reviews Genetics, 7, 401–405. Warburton, C. (1890). The spinning apparatus of geometric spiders. Quarterly Journal of Microscopical Science, 31(2), 29–40. Warburton, C. (1909). Arachnida embolobranchiata (scorpions, spiders, mites etc.). In S. F Harmer, & A. E. Shipley (Eds.). The Cambridge natural history volume IV (pp. 295– 473). London: Macmillan and Co. Whitfield, J. (2006). The beat of a heart: life, energy and the unity of nature. Washington: Joseph Henry Press. Worthington, A. M. (1895). The splash of a drop. London: Society for Promoting Christian Knowledge. Worthington, A. M. (1908). A study of splashes. London, New York, Bombay, Calcutta: Longmans, Green & Co.
applications. London & New York: Spon & Chamberlain. Darling, C. R. (1914). Liquid drops and globules: Their Formation and movements. London & New York: Spon & Chamberlain. Daston, L., & Galison, P. (2007). Objectivity. New York: Zone Books. Esposito, M. (2013). Romantic biology, 1890–1945. London: Pickering & Chatto. Esposito, M. (2014). Problematic “idiosyncrasies”: Rediscovering the historical context of D'arcy Wentworth Thompson's science of form. Science in Context, 27(1), 79–107. Gliboff, S. (2015). Breeding better peas, pumpkins, and peasants: The practical mendelism of erich tschermak. In D. Phillips, & S. E. Kingsland (Eds.). New perspectives on the history of life sciences and agriculture (pp. 419–439). New York: Springer-Verlag. Gould, S. J. (1971). D'Arcy Thompson and the science of form. New Literary History, 2(2), 229–258. Gould, S. J. (2002). The structure of evolutionary theory. Cambridge: Harvard University Press. Jarron, M. (2013). Editorial. Interdisciplinary Science Reviews, 38(1), 1–11. Keller, E. F. (2002). Making sense of life: Explaining biological development with models, metaphors, and machines. Cambridge: Harvard University Press. Maartens, A. (2017). On Growth and form in context – an interview with matthew jarron. Development, 144(23), 4199–4202. Miall, L. C. (1892). The surface-film of water, and its relation to the life of plants and animals. Nature, 46(1175), 7–11. Ridley, M. (1986). Embryology and classical zoology in great Britain. In T. Horder, J.
8
Contents lists available at ScienceDirect
Studies in History and Philosophy of Biol & Biomed Sci journal homepage: www.elsevier.com/locate/shpsc
Imitating nature: Analogy and experiment in D'Arcy Thompson's Science of Form
T
Matthew Holmes Centre for Research in the Arts, Social Sciences and Humanities, Alison Richard Building, 7 West Road, Cambridge, CB3 9DT, UK
A B S T R A C T
D'Arcy Wentworth Thompson's “Science of Form” – the explanation of biological development and morphology through physical forces and mathematical laws – has traditionally been viewed as an idiosyncratic, even heretical, episode in the history of evolutionary biology. Yet recent scholarship has sought to overturn this view by demonstrating that Thompson was active in contemporary scientific networks. This paper argues that a key influence upon Thompson's seminal work, On Growth and Form (1917), may be far more practical, and lie closer to home, than previously realised: experimental demonstrations of basic concepts in physics. Harnessing previously unpublished archival sources, this paper traces Thompson's correspondence with Charles Darling, Arthur Worthington and Cecil Warburton. In these exchanges, Thompson described his own experiments, or requested that experiments be conducted on his behalf. This correspondence, and its subsequent inclusion in the first edition of On Growth and Form, revises our current picture of Thompson from that of an abstract thinker to keen experimentalist. Moreover, his contact with physicists indicates that simple experiments enabled extensive crosstalk between early twentieth century physics and biology.
At the 1894 meeting of the British Association, D'Arcy Wentworth Thompson (1860-1948), Professor of Biology at the University of Dundee, went on the attack against Darwinism. A subsequent account reported that Thompson explained that “the profusion of forms, colours, and other modifications” in the natural world were “due merely to laws of growth” (Anonymous, 1894, p. 435). Thompson also took issue with existing Darwinian explanations for organic forms; for example, that the peculiar shape of the guillemot's egg was an evolutionary adaption for a seabird which nests on the faces of cliffs. The pointed egg of the guillemot had supposedly evolved to roll on its axis when nudged, rather than tumbling into the sea.1 This, thought Thompson, was nonsense. The shape of the guillemot's egg was “merely the natural result of the pressure caused by a relatively large egg passing down a narrow muscular passage” (Anonymous, 1894, p. 435). Thompson (1908, pp. 111-112) would further develop his ideas, arguing that we should first attempt to account for an organic form by recourse to the “simple physical lines with the forces to which it has been subjected.” This maxim would inform Thompson’s (1917) most famous work, On Growth and Form. The first edition of On Growth and Form was a monumental work, designed to persuade its readers that basic physio-chemical forces shaped the organism at every level through extensive use of comparison and analogy. On the smallest scale, he noted that spindle-like structures present during cell division bore a “striking resemblance” to iron filings shaped into lines of force by the poles of a magnet (Thompson, 1917, p.
169). Several orders of magnitude higher and the influence of physical forces on the organism was still apparent. Thompson (1917, p. 682) told his readers the story of how Carl Culmann, a German engineer, had been taken aback when visiting the laboratory of biologist Hermann Meyer. When Culmann spotted Meyer's drawings and specimens of bones, he was astounded to recognise lines of tension and stress identical to those in his engineering projects. These few examples indicate that Thompson's “Science of Form” – the explanation of morphology through physical forces and mathematical laws – was not only an ambitious biological research programme, but also depended upon input from other sciences (Gould, 1971). Yet its relationship to some of the pressing issues of early twentieth-century biology, notably the validity of vitalism, mechanism and organicism, remains ambiguous (Esposito, 2014, p. 91; Maartens, 2017. p. 4202). Thanks in part to his rebuttal of Darwinian explanations, Thompson's Science of Form has sporadically been depicted as an idiosyncratic, even heretical, episode in the history of evolutionary biology.2 Stephen Jay Gould (1971) initially portrayed Thompson as a lone and isolated genius. To his credit, Gould (2002, p. 1183) later backtracked on this interpretation, admitting that he had been “beguiled by D'Arcy Thompson's seemingly anachronistic peculiarities.” More recent scholarship has also sought to overturn this idiosyncratic attraction. Maurizio Esposito (2013; 2014) has argued that Thompson was not an isolated figure, but by the time the second edition of On Growth and Form was published in 1942 was part of a network of like-
E-mail address: [email protected]. An engaging and accessible account of the long-running controversy over the guillemot's egg is given in Birkhead (2016). 2 Some examples include Ridley (1986), Wallace (2006), Whitfield (2006) and Ball (2013). 1
https://doi.org/10.1016/j.shpsc.2019.101181 Received 13 November 2018; Received in revised form 25 April 2019; Accepted 23 June 2019 Available online 28 June 2019 1369-8486/ © 2019 Elsevier Ltd. All rights reserved.
Studies in History and Philosophy of Biol & Biomed Sci 78 (2019) 101181
M. Holmes
manufacture an early fire alarm by inserting a platinum wire into the top of a mercury thermometer. In the event of a fire, the rising mercury would push the wire upward, completing a circuit which would sound an alarm bell. Yet upon his appointment as Lecturer in Science, Darling turned to the study of water droplets and globules. While this subject admittedly did not carry the same practical implications as fire alarm design, it did allow him to unleash his considerable creativity in experimental physics. During a popular lecture series at the City and Guilds Technical College, later published as Liquid Drops and Globules: Their Formation and Movements, Darling (1914, pp. 8-10) examined the shape of detached liquid droplets. He began by smearing a glass plate with grease, to prevent fluid from adhering to it, before adding a series of water droplets to the glass from a pipette. A projector displayed the water drops on a screen for the benefit of his audience, as Darling (1914, pp. 9-10) described his findings: “The larger drops are flattened above and below,” he remarked, “possess rounded sides and resemble a teacake in shape. Those of intermediate size are more globular, but still show signs of flattening; whilst the very small ones, so far as the eye can judge, are spherical.” Darling explained that the shape of the water droplets resting on his glass plate was the result of their size. Despite “the tendency of drops to become spherical,” the “influence of gravitation” was too much for the larger drops to bear, forcing them into an elongated shape (Darling, 1914, p. 10). Only by cancelling out the effects of gravity could one observe perfect spheroids. This feat could be accomplished using floating soap bubbles or suspending oil globules in alcohol (Darling, 1914, pp. 10-11). This demonstration of the shape of water droplets on glass caught the eye of D'Arcy Thompson, then Professor of Biology at the University of Dundee. On February 18th, 1915, Thompson wrote to Darling to compliment his book and its improvements to the experiments of French physicist Felix Plateau. Thompson primarily, however, sought to enlist Darling's help with what he termed a “little biological problem,” of which he was “not mathematician enough to work out.“6 This problem was how to explain the different shapes of sea urchins. “I have a strong idea,” elucidated Thompson in his letter, “that the form of a seaurchin might be explained as an elastic surface deformed by gravity, very much like a drop resting upon a glass plate.“7 He then compared Darling's images of elongated water drops to the shapes of different sea urchins he had observed. Ever the master of understatement, Thompson explained that Darling's book has so enthralled him as “because I am, at this moment, trying to write a little book on the relation of organic forms to the physical forces, a job for which I have plenty of enthusiasm but a sad lack of mathematical skill.“8 This little book was, of course, the gargantuan On Growth and Form. Darling, flattered by Thompson's letter, set to work trying to match the form of sea urchins to his droplets. “With regard to the forms of seaurchins depicted in your card of drawings,” Darling responded in a letter dated February 22nd, “most of them can easily be reproduced in outline by the aid of liquids of approximately equal density to water.“9 Darling had his greatest success replicating the forms of the Coelopleurus genus and Urechinus species of sea urchins, both of which possess an “acute point” and closely resemble a typical water droplet on a flat surface. This form, Darling reported, was “nearly identical in shape with globules I have frequently obtained, in which, on standing, bubbles of gas rose to the summit and pressed the skin upwards without being able to escape.“10 The form of these sea urchins could thus be
minded “romantic” biologists. These included “A. Dalcq, H. Przibram, E. Hatschek, E. Conklin, J. Huxley, F Lillie and, of course, Haldane” (Esposito, 2014, p. 67).3 Yet the question of which scholars and traditions influenced Thompson prior to 1917 and the publication of the first edition of On Growth and Form remains tantalisingly open.4 Far from the Science of Form being an example of isolated, “bluesky thinking,” this paper argues that a formative influence upon Thompson and the first edition of On Growth and Form (1917) was far more practical: experimental demonstrations of basic concepts in physics.5 Harnessing previously unpublished correspondence from the D'Arcy Thompson Collection, this paper examines the exchange of ideas between Thompson and contemporary figures in physics and biology. The use of experiment in this correspondence and subsequent publications raises some intriguing possibilities for our understanding of the Science of Form. First, it confirms that Thompson was never an isolated scholar but was part of a far-reaching scientific network of physicists and naturalists. Second, it confirms that the Science of Form was more reliant on experiment than has been previously recognized. At least some of the key ideas posed in On Growth and Form were based on household experiments and the similarities between inorganic and organic forms produced during these experiments. This paper is divided into three parts. The first examines Thompson's exchange with the London physicist and lecturer Charles Robert Darling. Darling was an authority upon the behaviour of liquid droplets and, encouraged by Thompson, attempted to ascertain whether he could use these to imitate the shapes of various sea urchins. The second part explores Thompson's failed attempt to enlist the aid of Arthur M. Worthington. A physics professor at a Naval College, Worthington shot to scientific acclaim through his work on splashes. Thompson sought, unsuccessfully, to elicit Worthington's aid by comparing the form of splashes with biological structures and giving accounts of his own experiments. The final section of this paper analyses the correspondence between Thompson and Cecil Warburton. Following an exchange with Warburton, a zoologist and Entomologist to the Royal Agricultural Society, Thompson would contact Charles Vernon Boys, author of a popular textbook on experiments with bubbles. What emerges from these interactions is a newfound sense of Thompson as a minor, albeit creative, experimentalist, harnessing everyday objects in his quest to demonstrate how physical forces shaped biological forms. 1. Droplets and sea urchins “A drop of liquid is one of the commonest things in nature,” Charles Robert Darling noted (1914, p. 1), “yet it is also one of the most wonderful.” Darling was a Lecturer in Science at the City and Guilds Technical College in London, an organisation founded in the late nineteenth century to provide a technical education for craftsman and engineers. An itinerant lecturer and industrious author, Darling's wideranging publications reflected the demands of his audience. One of his early publications, on “Industrial Pyrometry,” emerged from a series of lectures delivered to the Royal Society of Arts (Darling, 1911, p. xi). In 1912, while an associate of the Royal College of Science in Dublin, Darling (1912, p. 84) produced a guide to the practical applications of heat for engineers. One passage in the book explained how to 3
Thompson's collaboration with E. Hatschek and Hans Leo Przibram, as described by Esposito (2014), provide valuable evidence for claim that Thompson was strongly influenced by experimental demonstration. Yet for reasons of brevity, this paper restricts itself to the period prior to the publication of the first edition of On Growth and Form (1917). 4 A general overview of Thompson's life and career can be found in a biography by his daughter, Ruth D'Arcy Thompson (1958). 5 A similar turn towards the practical and everyday has occurred in the historiography of Mendelism and early genetics, which now looks increasingly towards agriculture. See Gliboff (2015).
6 All archival sources cited in this paper are located in the Special Collections of the University of St Andrews Library. The Call Number (MS) is given for ease of access. MS 19100. 7 MS 19100. 8 MS 19100. 9 MS 19102. 10 MS 19102.
2
Studies in History and Philosophy of Biol & Biomed Sci 78 (2019) 101181
M. Holmes
explained, a sea urchin was essentially “a spherical shell symmetrically depressed under the influence of gravity.” Thompson (1917, p. 664) also referred to his correspondence with Darling, whom he characterised as “an acknowledged expert in drops,” at length. He described how Darling had attempted to recreate the shape of sea urchins using drops and had only run into difficulty with the troublesome Asthenosoma and its lantern. Thompson (1917, p. 664) also described the analogy between bubbles of gas in Darling's drops and ova in sea urchins. On Growth and Form ultimately included two citations from Darling's first letter of February 22nd: the first on the ease of reproducing the form of sea urchins using drops and the second describing how bubbles of gas could push drops into a conical shape reminiscent of the Coelopleurus and Urechinus urchins (Thompson, 1917, pp. 663-664). Thompson's correspondence with Darling, and its later inclusion in On Growth and Form, is striking for several reasons. The first is that a sophisticated and convincing case study in Thompson's Science of Form was derived from popular, even elementary, physics. Darling, a travelling lecturer based at a technical institution, was far from a prestigious figure in the scientific community. His experiments, comprising of droplets of water and dripping syrup, possessed a distinctly homemade feel. Almost as striking as the simplicity of Darling's experiments was his lack of mathematics. Thompson had complained of his own lack of mathematical skill when he had first written to Darling on February 18th. Yet Darling showed no inclination to provide Thompson with his desired mathematical explanation of the form of sea urchins. In fact, the physicist was dismissive of the idea. “So far,” wrote Darling, “I have received little assistance from the mathematical side of the subject.“18 Most mathematical work on surface tension had apparently been devoted to the skins of globules, rather than explaining the stability of unusual shapes such as liquid columns (Darling, 1914, p. 43). “How far mathematical investigations would assist the discovery of phenomena of this kind it is impossible to say,” Darling informed Thompson, “but certainly a great deal can be done without it. The variety of forms obtainable is almost endless.“19 The case of the sea urchin tells us that Thompson was not merely content with observing that organic and inorganic forms were shaped by the same physical forces. He was also prepared to directly compare aspects of the material world with that of the biological. For Thompson, a lack of any mathematical understanding of the form of droplets and sea urchins was an unfortunate downside of this comparison. Yet far from being a purely theoretical or mathematical thinker, Thompson was more than willing to collaborate with a practically-minded physicist on simple experiments. The sea urchin also leads to what is in part a historian's caveat, in part a reason for admiration. We have just examined how Darling's lectures and experiments interacted with Thompson's Science of Form. Yet the sea urchin was only allocated some five pages of the 1917 edition of On Growth and Form (Thompson, 1917, pp. 661-665). In part, this outcome reflects the sheer investment and resources Thompson poured into his book. Yet it also indicates that we should remain cautious before drawing any firm conclusions about the significance accorded to elementary physics experiments in the Science of Form. In the remainder of this paper, we shall examine some further instances of Thompson's engagement with household experiments, which reveal that he was not only intrigued by such experiments, but quite capable of carrying out his own.
explained as a contest between gravity and these rising bubbles. Gravity distorted the sea urchin into an elongated shape, while bubbles under its elastic surface pushed the top of the sea urchin upwards to form their points. Yet there was one sea urchin whose form, explained Darling, continued to elude him: “The Asthenosoma appears the most difficult, as although I can reproduce either half easily, it may prove difficult to get the two together. As soon as possible I will get the camera to work, and let you see the results.“11 Darling's experiments reinforced Thompson's faith in his interpretation of the form of sea urchins. Only two days after Darling's response, Thompson fired off another letter to address “what you [Darling] say about the urchins with an acute point as being comparable to globules that contain gas bubbles, I had already thought of the same idea, though not quite in the same way.” Thompson pointed out that sea urchins contain “large masses of ova and these are laden with oil.” These ova, explained Thompson, were “concentrated towards the apex [of the sea urchin] and this is just the condition which occurred to me as accounting for the vertically elongated and pointed conformation of the shell.12 The sea urchin was then, at its most basic level, a liquid droplet held in an elastic film. It was flattened toward the sea floor by gravity but rose to a central point thanks to its oil-coated ova. Thompson also provided an apologetic explanation for the troublesome Asthenosoma, which he confessed he should not have included in his set of drawings. “The form [of the Asthenosoma],” he explained, “is complicated by the large solid mass of the “Aristotle's lantern” [the sea urchin's mouthpiece] inside the flexible, membraneous shell.“13 The presence of the Aristotle's lantern altered the shape of the sea urchin in a manner which Darling could not have replicated with liquid droplets alone. With the sea urchin conundrum effectively solved, Thompson now turned to the form of the lagena genus of the foraminifera: tiny, singlecelled marine organisms, possessing a shell and thread-like ectoplasmic strands. In his Liquid Drops and Globules, Darling (1914, pp. 7-8) had used syrup to demonstrate how liquids droplets attempted to keep a spherical shape. By watching syrup drip off a glass rod, Darling (1914, p. 7) claimed to have witnessed “a remarkable property of a liquid surface,” its “tendency, as in the case with all stretched membranes … to reduce the area of [its] surface to a minimum.” Although this tendency, at least in the case of syrup, would be overwhelmed by the force of gravity, once a droplet of syrup fell it would immediately assume its spherical shape once more (Darling, 1914, p. 8). This experiment came as encouraging news to Thompson, who in his letter of February 24th wrote that “I have long had an idea that the little foraminiferal shells called lagena were formed as so many hanging drops, but the difficulty was to find evidence that they really hang.“14 Thompson noted that cross-sections of the nodosaria genus revealed “the necks of the little bottle-shaped lagenae fitting one into another.“15 Perhaps these shells upon shells had been formed by hanging drops, as “the first-formed lagena accumulating a new drop of protoplasm and within as it were falling so far through the new drop while the whole system hung by the contact between this latter and the surface water-film.“16 Sadly for this latest theory, a brief reply by Darling on the 27th February informed Thompson that further research on the matter would be required.17 What impact then, did this exchange have on the published version of On Growth and Form? Thompson (1917, p. 662) once again relayed his vision of the sea urchin as the product of an “equilibrium of forces.” Just like a drop of water on a plate, Thompson (1917, p. 663)
2. Splashes and hydroids 11
MS MS 13 MS 14 MS 15 MS 16 MS 17 MS 12
“The splash of a drop is a transaction which is accomplished in the twinkling of an eye,” Arthur M. Worthington acknowledged (1895, p. 7) during his 1894 lecture at the Royal Institution, “and it may seem to
19102. 19101. 19101. 19101. 19101. 19101. 19102.
18 19
3
MS 19102. MS 19102.
Studies in History and Philosophy of Biol & Biomed Sci 78 (2019) 101181
M. Holmes
Worthington's work primarily stemmed from two areas of interest: “(1) the regular and beautiful notching of the little cups or calycles of certain zoophytes and (2) the appearance of a beautiful and regular pattern of ridges and furrows upon the shells of certain Foraminifera (Lagenae).“22 Thompson's theorising on the shape of Lagenae shells had met a dead end with Darling some several months earlier. Undeterred, Thompson repeated his assertion that the form of their shells resembled “hanging drop” to Worthington.23 Thompson also attached “two or three pages” of his draft manuscript regarding calycles to the letter, “That you might better understand the lines on which I am going.“24 Thus far, Thompson's typed letter was typical of the many he dispatched over the course of 1915: highly complimentary and inquiring into one or two biological phenomena he felt were most amenable to the insight of physicists. Yet toward its conclusion, the tone of his letter to Worthington changed. “While I have this opportunity of writing to you,” recalled Thompson, “I am reminded of a little experiment that I made many years ago and thought no more of.“25 He went on to describe a curious formation he had once found in his local brickfields. These formations consisted of “(1) of a quoit-like ring of hardened clay and (2) of a very smooth and regular oblate spheroid of the same material, resting upon the former.“26 Although geologists were reportedly baffled, Thompson thought that these spheroids and their rings had been formed by splashes. He reported that he “was able to imitate them very closely by splashing drops of water onto a dish of fine sand.“27 These splashes wet the sand, causing it to draw together and create a spheroid. The water then drained from the spheroid, wetting the surrounding sand to create a concentric ring. “I tried a few other experiments with such substances as plaster of Paris,” recalled Thompson, “with considerable success.“28 In a 1916 letter to the mathematician George Greenhill, Thompson complained that his appeal to Worthington had gone unanswered: “[I] not want to think evil of him, but in my last [letter] I besought him for a postcard."29 Yet this setback did not prevent Thompson from further pursuing the link between splashes and animal forms, nor from drawing upon Worthington's studies in the first edition of On Growth and Form (1917). Chapter Five of On Growth and Form takes the reader through the theories of Plateau and goes into great detail describing his experiments on the separation of a liquid cylinder into droplets (Thompson, 1917, pp. 227-229). The competition between the outward pressure of a liquid and the inward pressure of its surface tension could, according to Thompson (1917, pp. 235-236), explain a huge range of phenomena. Following in Worthington's footsteps, Thompson (1917, p. 236) described the notched edges of a wave approaching a shore as a consequence of surface tension being overwhelmed. The shape of splashes could also be explained using Plateau. “In some of Mr. Worthington's most beautiful experiments on splashes,” explained Thompson (1917, pp. 235-236), “it was found that the fall of a round pebble into water from a considerable height, caused the rise of a filmy sheet of water in the form of a cup or cylinder; and the edges of this cylindrical film tended to be cut up into alternate lobes and notches.” The shape of a splash reminded Thompson (1917, p. 236) “of the beautifully symmetrical notching on the calycles of many hydroids, which little cups before they became stiff and rigid had begun their existence as liquid or semi-liquid films.” The liquid-like film which formed the distinctive cup of young hydroids, tiny ocean-dwelling animals, was naturally unstable. This instability led to segmentation,
some that a man who proposes to discourse on the matter for an hour has lost all sense of proportion.” Worthington, Headmaster and Professor of Physics at the Royal Naval Engineering College in Davenport, of course spent his lecture attempting to undermine this proposition. Worthington (1895, pp. 8-9) had long been fascinated by splashes, ever since when a schoolboy at Rugby he had accidentally dripped ink onto some smoked glasses and reported the formation of fine concentric rings to the Rugby Natural History Society. Worthington (1895) had first attempted to capture the shape of splashes using flashes of light and the naked eye, before moving onto new photographic technology.20 The final result of Worthington's efforts to describe and capture the splash of water droplets was an acclaimed monograph, A Study of Splashes, published in 1908. As if to affirm both his military credentials and the practical applications of his chosen science, the first photograph in the book was that of the metallic “splash” created when a projectile penetrated an armoured plate (Worthington, 1908, p. iv). Worthington (1908, p. 1) began his study by noting that many of his readers, caught in a shower of rain, may have watched “half-subconsciously, the thousand little crystal fountains that start up from a surface of pool or river; noting now and then a surrounding coronet of lesser jets, or here and there a bubble that floats for a moment and then vanishes.” Yet despite the ubiquity and our everyday experience of falling drops, the sequence of the splash, which occurs “within the limits of a few hundredths of a second … taxes the highest mathematical powers to elucidate” (Worthington, 1908, pp. 1-2). Surface tension was key to understanding the shape of drops and their behaviour once they hit a solid or liquid surface. “The first principle to be understood,” explained Worthington (1908, p. 32), “is that the surface layers of any liquid behave like a uniformly stretched skin or membrane, which is always endeavouring to contract and to diminish its area.” Hanging drops existed, at least temporarily, thanks to this principle. Worthington (1908, p. 33) described how the stretched skin on a hanging drop pressed back upon its contents, preventing the liquid from simply flowing away. Darling (1914, p. 7) would reiterate the same argument in his own book some six years later. Worthington (1908, p. 36) also expanded upon the demonstration first performed by the “blind Belgian philosopher Plateau,” that a cylinder of liquid could not remain “of stable equilibrium if its length exceeds about 3 1/7 times its diameter.” Once beyond this ratio, the inward pressure of surface tension would overwhelm the outward pressure of the liquid and the cylinder would split into drops. This transition from stable equilibrium to instability and segmentation could be readily observed in nature. Worthington (1908, p. 39) explained how waves approaching a beach initially have a “smooth, horizontal cylindrical edge,” from which “at a given instance, are shot out an immense array of little jets which speedily break into foam, and at the same moment the back of the wave, hitherto smooth, is seen to be furrowed or combed.” These jets and furrows occurred thanks to the same laws Plateau had proposed to explain the segmentation of liquid columns. The power of surface tension to shape nature could also be seen in “the dimples made by the weight of an aquatic insect, where its feet rest on the surface without penetrating it” (Worthington, 1908, p. 35). Fresh from his exchange with Darling, Thompson wrote to Worthington on November 24th, 1915, ostensibly to ask for his permission to reproduce some figures from A Study of Splashes. Yet Thompson, as ever, was also interested in a physicist's take on his forthcoming book, On Growth and Form, which he explained to Worthington as “an attempt to bring elementary physics and elementary mathematics to bear upon the great variety of matters connected with organic morphology.“21 Thompson stated that his allusions to
22
MS MS 24 MS 25 MS 26 MS 27 MS 28 MS 29 MS 23
20 Worthington is familiar to historians and philosophers of science through the work of Lorraine Daston and Peter Galison (2007) on objectivity. 21 MS 29564.
4
29564. 29564. 29564. 29564. 29564. 29564. 29564. 28662.
Studies in History and Philosophy of Biol & Biomed Sci 78 (2019) 101181
M. Holmes
which appeared in the formation of ridges, furrows and notches. “In the case of the hydroid calycle,” wrote Thompson (1917, p. 237), “we are led to the conclusion that the two common and conspicuous features of notching or indentation of the cup, and of constriction or annulation of the long cylindrical stem, are phenomena of the same order and are due to surface tension, in both cases alike.” Thompson, in essence, saw the cups of hydroids as analogous to a splash. The ridges on their cups and the notches at their edge spoke of the same physical forces which created Worthington's carefully captured splashes. Similarly, Thompson viewed hydroids' long stems as a Plateau's cylinder in the process of segmentation. As the hydroid matured and its cup and stem hardened, these morphological manifestations of liquid instability were forever frozen upon its surface. What role, then, did Thompson's own experiments play in this episode? Even with the aid of photography, liquid splashes were quick and difficult to study. Yet, noted Thompson (1917, p. 238), “we can repeat and demonstrate many of the simpler phenomena, in a permanent or quasi-permanent form, by splashing water on to a surface of dry sand, or by firing a bullet into a soft metal target.” On one level, Thompson's experiments with sand and plaster of Paris were a means of capturing the splash for study in such a permanent form. Yet these experiments also proved to serve another point. “There is nothing,” argued Thompson (1917, p. 238), “to prevent a slow and lasting manifestation, in a viscous medium such as a protoplasmic organism, of phenomena which appear and disappear with prodigious rapidity in a more mobile liquid.” A parallel had once again been drawn between the organic and the inorganic. The legacy of the physical forces which shape waves and splashes could be found in brickfields, in a dish of sand or on a hydroid. Glassmaking and pottery provided analogies of how an equilibrium of forces could create a simple form. Yet Thompson (1917, p. 239) complained that “we are for the present on the uncertain ground of suggestion and conjecture.” Even the simplest of organic forms, including sea urchins and hydroids, could not yet be described in mathematical terms. Although Thompson never managed to engage Worthington with his Science of Form as he did Darling, his attempt to do so is nonetheless instructive. Again we can see that Thompson was fascinated by simple experiments and willing to reach out to physicists outside the university. He was also prepared to draw close parallels between inorganic and organic forms. Geological formations could be replicated through experiment. In turn these experiments revealed the fundamental forces of nature, which shaped organic forms. Both hydroids and the brickfield formations were analogous to a drop of water in a dish of sand. Yet on this occasion Thompson did not outsource experimental work, as he had with Darling and his queries into the form of sea urchins. Thompson had carried out basic experiments of his own accord and attempted to engage Worthington with his findings. Had he been successful in soliciting Worthington's interest, his sand experiments may well have played a more significant role in On Growth and Form than they did (Thompson, 1917, p. 238). In lieu of a developed experimental programme, Thompson instead relied upon the authority of Worthington and analogies with industrial techniques to make his case for the form of the hydroid.
was to sit on a committee charged with ridding the ceiling of Westminster Hall of an infestation of Death Watch beetles (Clark, 2009, p. 214). When his services were not demanded by Parliament, Worthington explored the lives of spiders, mites and ticks. The former, however, were his greatest passion (Tate, 1958, p. 1771). Warburton (1890, p. 29) soon established a name for himself in arachnology with a paper on the spinning glands of spiders. A chapter in The Cambridge Natural History, to which Thompson was also a contributor, further cemented Warburton's reputation as a premier arachnologist. In his lengthy treatment of spiders, Warburton (1909, p. 343) discussed how some spiders wove circular webs of “parallel silken lines … varying in number according to the special purpose for which they are designed, and sometimes adhering more or less to one another on account of their viscidity and closeness.” Yet Warburton was not content to merely observe webs in the field. After all, one could quite easily “carry off a newly-constructed web – or, better still, one not quite finished – on a piece of plate glass, to which it will adhere by reason of the viscid spiral, and on which it may be examined at leisure” (Warburton, 1909, p. 347). Once arranged on the glass, a staining fluid could be added to the web, revealing its hidden structure. “It will appear to consist,” reported Warburton (1909, p. 347), “of a thread strung with beads of two sizes, occurring with pretty uniform alternation, though two of the larger beads are often separated by two or more of the smaller.” This phenomenon, noted Warburton (1909, p. 348), was a consequence of the “viscid matter” on the thread arranging itself into the beads. At an 1889 lecture at the Royal Institution, the physicist Charles Vernon Boys had declared that he had been able to replicate the formation of these beads in quartz fibres. “A liquid cylinder, as Plateau has so beautifully shown,” Boys (1889, pp. 249-250) reminded his audience, “is in an unstable form.” Just as such a cylinder would break up into separate droplets, so a cylinder or thread of liquid quartz would “break up into spheres” (Boys, 1889, p. 250). As the quartz cooled into a solid, the spheres would disappear: “thus completely agreeing with the results of Plateau's investigations” (Boys, 1889, p. 250). Boys was even able to replicate the sticky liquid which spiders coated on their webs to catch flies. By coating a quartz fibre with castor oil, Boys (1889, p. 250) observed the emergence of “beaded threads,” which made his fibres appear “quite indistinguishable from a real spider web and … just as good at catching flies.” The following year, at the meeting of the British Association in Leeds, Boys blurred the boundaries between the organic and inorganic still further. His quartz fibres were identical in appearance to the thread of a spider's web, leading him to the question of “what a spider would do if by any chance she should find herself on such a [quartz] web” (Boys, 1890, p. 606). In front of a live audience, Boys (1890, p. 606) set about trying to transfer three small spiders from their own webs onto his quartz replicas. His demonstration did not go entirely to plan: “Unfortunately this spider has slipped and has got away,” Boys (1890, p. 250) informed onlookers, “but with another I am more successful.” His plan had been to show how the spiders would struggle to climb the smooth quartz fibres without the presence of liquid spheres. Yet the particularly stubborn spider was able to climb the quartz (Boys, 1890, p. 250). Despite such difficulties, Warburton (1909, p. 348) was convinced that Boys was correct. The formation of liquid beads on a spider's web was a purely mechanical process. In addition to manhandling uncooperative spiders in front of the British Association, Boys was also an educationalist. Over the winter of 1889–1890 he delivered a lecture course at the London Institution to a young audience. The lectures, later published by the Society for Promoting Christian Knowledge as Soap-Bubbles and the Forces Which Mould Them, began with what is now a familiar trope. “I do not suppose that there is any one in this room who has not occasionally blown a common soap-bubble,” ventured Boys, “and while admiring the perfection of its form, the brilliancy of its colours, wondered how it is that such a magnificent object can be so easily produced” (Boys, 1896, p. 9).
3. Globules and spiders’ webs The life of a budding naturalist is sometimes a tense one. “The 75 spp. [multiple species] of exotic spiders arrived safely,” reported a young Cecil Warburton to D'Arcy Thompson in 1899, although “The spirit had about all left the tubes, but luckily I was able to fill them up before they dried.“30 A Cambridge zoology graduate, Warburton had succeeded the esteemed Eleanor Ormerod as Consultant Entomologist to the Royal Agricultural Society in 1892. One of his newfound duties 30
MS 22768. 5
Studies in History and Philosophy of Biol & Biomed Sci 78 (2019) 101181
M. Holmes
the wire, the varnish would divide into globules. Having interrogated Warburton on the viscid globule, Thompson moved to contact Boys. Yet their exchange, according to surviving letters, did not begin until 1920. By this time, On Growth and Form had finally been delivered to Cambridge University Press and published, to great acclaim. On June 19th, 1920, Boys – responding to a missing letter of Thompson's – wrote with instructions on how to produce a light spectrum using an arc lamp.39 It was only in a later letter, written on October 28th, 1921, that Boys finally discussed bubbles with Thompson. Boys confessed that he could “do nothing” to help Thompson with his inquiries. Over the years he had lost or mislaid much of his material on the subject and had “never seen them since or blown a bubble.“40 Boys did, however, direct Thompson to his textbook. “So follow the directions at the end of my book very diligently,” wrote Boys, jokingly adding “with piety,” and directed Thompson to other authors.41 By this time, Boys (1920, pp. 188-190) was probably referring to an updated edition of his textbook, which discussed the use of electricity to merge bubbles in its end pages. This one-sided exchange indicates that Thompson was belatedly interested in Boys' work on bubbles and was attempting to replicate his experiments. Although Thompson's attempted experiments with bubbles came too late for inclusion in the first edition of On Growth and Form, spiders' webs and their globules did appear in the book. “In the spider's web,” wrote Thompson (1917, p. 231-232), we find exemplified several of the principles of surface tension which we have now explained.” Thompson (1917, p. 232) described how spiders secreted two forms of viscous fluid when constructing their webs. The first issued from the body as a semi-fluid, drying upon exposure to air. The second secretion maintained its fluid form for several hours, coating the web as a liquid cylinder. During this drying period, a slow-motion demonstration of Plateau's limit to the length of liquid cylinders could be observed. Thompson (1917, p. 232) explained that this cylinder “disrupts in the usual manner, passing first into the wavy outline of an unduloid, whose swollen portions swell more and more till the contracted parts break asunder.” By the time this process was complete, “a series of spherical drops or beads, of equal size [were] strung at equal intervals along the thread.” To further illustrate his account, Thompson (1917, p. 232) referred to the household experiment he discussed in conversation with Warburton: “If we try to spread varnish over a thin stretched wire, we produce automatically the same identical result.” Once again, Thompson's engagement with Warburton – and more indirectly Boys – demonstrates that he was able to reach out to a larger scientific network whilst constructing his Science of Form. This network consisted of naturalists and physicists, both of whom could be engaged with basic experiments and analogies. The story of the spiders' webs also demonstrates that Thompson was not alone in this ambition. Boys and his quartz webs at the British Association in 1889 represent perhaps one of the most blatant attempts to blur the boundaries between the organic and inorganic. Miall followed in Boys' footsteps with his Royal Institution lecture on aquatic organisms and surface tension in 1892. By the time that Thompson began to reach out to various scientists during the writing of On Growth and Form, there existed a receptive audience for his ideas. Mirroring his attempted interaction with Worthington, Thompson was again able to reach into his past to bring a basic experiment to bear on biological questions: this time the application of varnish onto a stretched wire. This experiment was, at least to Warburton, a novel one. Yet the case of Boys and Miall suggests that the days when biologists would be filled with “great wonder and admiration” by phenomena created through physical forces were numbered
To demonstrate how the elastic skin of bubbles was created by surface tension, Boys (1896, pp. 19-20) deployed a common piece of apparatus known as Van der Mensbrugghe's float. Consisting of a cork attached to a wire framework, the entire apparatus was forcibly submerged by Boys. As the cork attempted to rise, its wire frame pressed against the surface of the water with enough force to keep it submerged. Intriguingly, this same experiment was repeated at the Royal Institution on March 4th, 1892 by Louis Compton Miall (1842-1921), the first Professor of Biology at the University of Leeds. “It is necessary to the exposition of my subject,” declared Miall, “that I should begin by reminding you of some well-known properties of the surface of water … familiar to every student of physics.” (Miall, 1892, p. 7). Miall then proceeded to carry out a series of basic experiments, including Mensbrugghe's float. He used these demonstrations to argue that surface tension was a pervasive physical force which shaped the life of aquatic organisms. In what was perhaps a missed opportunity for both, Thompson and Miall's correspondence only reveals that they discussed matters of health and staff appointments at Leeds.31 Nor did Thompson initially seek to contact Boys over his work with bubbles or quartz rods. He instead, some fifteen years after his first exchange with the young naturalist, sought out Warburton's opinion on the formation of globules. Thompson contacted Warburton on February 9th, 1915 to request “any information regarding the variations in different species of the spider, of the form, size and number of the viscid globules on the web.“32 Referring to Warburton's piece in The Cambridge Natural History, Thompson also noted that “you [Warburton] credit Boys with discovery that these beads are formed automatically by surface tension … [yet] with all respect to Boys it was known to many long before his day.“33 Thompson recalled how, while studying physics at Cambridge during the 1870s, it was “a standing joke of Yate's part to laugh at the biologists who were innocent, and ignorant enough to think otherwise.“34 The jibe was presumably directed at those biologists who had no explanation for how these beads were created. The classic A History of the Spiders of Great Britain and Ireland by John Blackwall (1861, p. 10), for instance, estimated the number of these beads or globules on a typical web – somewhere in the region of 120,000 – but did not explain how they came to be. On February 16th Thompson wrote to Warburton once more. “Granting the physical hypothesis” of droplet formation on webs, mused Thompson, meant that such details “as the size and distance apart of the globules, must depend upon such variables as the thickness of the thread, the thickness of the superimposed viscid layer” and so on.35 Thompson requested new information from Warburton. He asked how the arrangement of globules on the web differed between spiders and if these differences “corresponded to the various differences which are theoretically possible.“36 Thompson also asked whether these differences could be correlated with “controlling factors,” such as the ratio of thread thickness to that of the liquid cylinders which coat it.37 Thompson did agree with Warburton that it was Plateau who had first hit upon the idea of the limits to stability in a liquid cylinder or column. Boys and his quartz fibres had demonstrated the applicability of Plateau's law on a microscopic scale. Yet a far simpler demonstration could be carried out in a domestic setting. Thompson described how “you could illustrate it every bit as well by tying a piece of thin copper wire (“binding” wire) to the door-knob, holding it tight and doing your best to brush over it a smooth coat of black varnish.“38 Instead of covering 31
See MS 22229 to 22233 for Miall and Thompson's Correspondence. MS 22771. 33 MS 22771. 34 MS 22771. 35 MS 22772. 36 MS 22772. 37 MS 22772. 38 MS 22772. Thompson also explained that he had encountered Plateau's work, including the latter's papers between 1843 and 1868, and Plateau's 1873 32
(footnote continued) book. 39 MS 11244. 40 MS 11245. 41 MS 11245. 6
Studies in History and Philosophy of Biol & Biomed Sci 78 (2019) 101181
M. Holmes
multiple offerings.” Is the experimental side of Thompson simply one of these highly selective perspectives? The wider correspondence discussed in this paper suggests that this is not the case. Thompson's letters to Worthington and Warburton demonstrate that experiment had long been an important part of his methodology and training. Far from being a throwaway line inserted into On Growth and Form, the use of experiment to draw analogies between the organic and inorganic was an important part of the Science of Form. The occasional reference to experiment in the published versions of On Growth and Form downplay the effort and thought Thompson and his collaborators put into their experimental programmes. Thompson's use of experiment also bears upon his wider use of mathematics. Contrary to what we might expect, On Growth and Form contains surprisingly few “actual equations, or even numbers,” instead relying upon “the laboratory manipulation of liquid drops, columns, solutions … contrived to mimic organic forms” (Keller, 2002, p. 65). Thompson's exchange with Darling in February of 1915 shows that Thompson was keen to establish a mathematical account of the different forms taken by sea urchins. Yet Darling was unable or unwilling to do so. The experimental recreation of sea urchins by Darling was therefore a substitute, or at least a first step, for a mathematics that did not yet exist. The lack of mathematics in the Science of Form was not necessarily due to lack of drive or ability on the part of Thompson. Keller (2002, p. 67) has argued that “Thompson's particular blend of diverse metaphysical traditions may have been idiosyncratic, but the component strands upon which he drew were well-established cultural resources.” One of these cultural resources was the experimental physics demonstrated in technical colleges, public lectures and households across Britain. Thompson was an experimentalist among many other experimentalists: a quality which might have made the first edition of On Growth and Form all the more appealing to his contemporaries.
(Thompson, 1917, p. 234). 4. Conclusion: D'Arcy Thompson the experimentalist? By tracing D'Arcy Thompson's use of experiments in On Growth and Form, this paper supports a growing sense of scepticism towards declarations of Thompson's isolation or idiosyncrasy. His pre-1917 correspondence suggests that Thompson was never entirely separated from a wider intellectual context. Just as Esposito (2013; 2014) places a latecareer Thompson within a European network of romantic biologists, so this paper places him within an experimentally-minded community. This community consisted of both fellow biologists like Warburton, and practically-minded physicists based at technical colleges. Thompson's exchange with Darling and attempted engagement with Worthington point to a new image of Thompson as a budding experimentalist. He suggested that Darling attempt to replicate the form of sea urchins through experiment and conducted his own with such commonplace items as varnish, copper wire and dishes of sand. As his successor in Dundee, Alexander Peacock, recalled: “Fortunate were all who saw him use sketches, bits of paper and string, and soap bubbles to explain the mathematics of the honeycomb, the nautilus shell and such like recondite things” (Jarron, 2013, p. 2). Why then, was Thompson so willing to use experiment to recreate natural forms, or demonstrate the applicability of physical forces to biological phenomena? The opening chapter to On Growth and Form provides one answer. Through correlation and equation, Thompson (1917, p. 6) argued, “the quest for physical causes merges with another great Aristotelian theme, – the search for relations between things apparently disconnected.” This refers to the Aristotelian philosophy of similitude. “Newton,” recounted Thompson, “did not shew the cause of the apple falling, but he shewed a similitude between the apple and stars.” In other words, Newton did not give an exact account of what gravity was. He did, however, show that the same physical force which causes apples to fall also causes stars to attract other celestial bodies and move in orbits. Similarly, the experiments conducted by or on behalf of Thompson showed how physical forces governed both organic and inorganic forms alike. Hence sea urchins were comparable to droplets, or splashes to hydroids. “The search for differences or essential contrasts between the phenomena of organic or inorganic, of animate and inanimate things has occupied many men's minds,” noted Thompson (1917, p. 7), “while the search for community of principles, or essential similitudes, has been followed by few.” According to Thompson's principles, basic physics experiments were not only a valid avenue of research but were integral to the Science of Form. Thompson, like many of his contemporaries, sensed that explaining the appearance of organic forms through appeals to evolutionary history was highly speculative (Esposito, 2014, p. 82). The Science of Form therefore rejected Darwinian explanations in favour of a system of forces acting upon the growing organism (Esposito, 2014, pp. 101-102). In the light of this context, the tabletop experiments conducted by Thompson and his collaborators must have held great appeal. Backed by the philosophy of similitude, it made sense that seemingly mundane objects and phenomena, such as droplets, splashes, sand and wire, operated under the same physical laws as those which shaped organic forms. Yet divorced from the complexity of biology, the workings of these laws could now be seen with greater clarity. Perhaps of even greater importance was that experiments recreated the conditions which shaped organisms for first-hand observation in real time. The contrast with the distinct and speculative nature of Darwinian explanations could not have been clearer. So how does a newfound perspective of Thompson as experimentally-minded and in pursuit of similitudes add to our current understanding of the Science of Form? Evelyn Fox Keller (2002, p. 62) states that one of the problems with working with On Growth and Form is simply that it is “a very large book, composed of many different parts, [and] it has been possible for readers to quite selectively draw from its
Acknowledgements My thanks go to the Special Collections staff at the University of St Andrew's Library, who were generous with their time and hospitality. I would also like to thank the organisers and attendees of the October 2018 History of Science, Technology and Medicine Network Ireland Annual Conference in Belfast, where I presented an early version of this paper. I owe a special debt of gratitude to the members of the History and Philosophy of Biology reading group at the University of Leeds, who first introduced me to the world of D'Arcy Thompson. Finally, I am grateful to two anonymous referees for their welcome feedback and suggestions. References Archival Sources D'Arcy Wentworth Thompson letters, archives of the Special Collections of the University of St Andrews Library.
Published Sources Anonymous (1894). Biology at the British association. Nature, 50(1296), 433–436. Ball, P. (2013). In retrospect: On growth and form. Nature, 494(7435), 32–33. Birkhead, T. (2016). The most perfect thing: Inside (and outside) a bird's egg. London: Bloomsbury. Blackwall, J. (1861). A history of the spiders of Great Britain and Ireland. London: Robert Hardwicke. Boys, C. V. (1889). Quartz fibres. Nature, 40(1028), 247–251. Boys, C. V. (1896). Soap-bubbles and the forces which mould them. London: Society for Promoting Christian Knowledge. Boys, C. V. (1890). Quartz fibres. Nature, 42, 604–608. Boys, C. V. (1920). Soap-bubbles and the forces which mould them. London: Society for Promoting Christian Knowledge. Clark, J. F. M. (2009). Bugs and the victorians. New Haven: Yale University Press. Darling, C. R. (1911). Pyrometry: A practical treatise on the measurement of high temperatures. London & New York: Spon & Chamberlain. Darling, C. R. (1912). Heat for engineers: A treatise on heat with special regard to its practical
7
Studies in History and Philosophy of Biol & Biomed Sci 78 (2019) 101181
M. Holmes
Witkowski, & W. Christopher (Eds.). A history of embryology (pp. 35–67). Cambridge: Cambridge University Press. Tate, P. (1958). Mr. Cecil Warburton. Nature, 182(4652), 1771. Thompson, D. W. (1908). On the shape of eggs, and the causes which determine them. Nature, 78(2014), 111–113. Thompson, D. W. (1917). On growth and form. Cambridge: Cambridge University Press. Thompson, R. D. (1958). D'Arcy Wentworth Thompson: The scholar-naturalist. Oxford: Oxford University Press. Wallace, A. (2006). D'Arcy Thompson and the theory of transformations. Nature Reviews Genetics, 7, 401–405. Warburton, C. (1890). The spinning apparatus of geometric spiders. Quarterly Journal of Microscopical Science, 31(2), 29–40. Warburton, C. (1909). Arachnida embolobranchiata (scorpions, spiders, mites etc.). In S. F Harmer, & A. E. Shipley (Eds.). The Cambridge natural history volume IV (pp. 295– 473). London: Macmillan and Co. Whitfield, J. (2006). The beat of a heart: life, energy and the unity of nature. Washington: Joseph Henry Press. Worthington, A. M. (1895). The splash of a drop. London: Society for Promoting Christian Knowledge. Worthington, A. M. (1908). A study of splashes. London, New York, Bombay, Calcutta: Longmans, Green & Co.
applications. London & New York: Spon & Chamberlain. Darling, C. R. (1914). Liquid drops and globules: Their Formation and movements. London & New York: Spon & Chamberlain. Daston, L., & Galison, P. (2007). Objectivity. New York: Zone Books. Esposito, M. (2013). Romantic biology, 1890–1945. London: Pickering & Chatto. Esposito, M. (2014). Problematic “idiosyncrasies”: Rediscovering the historical context of D'arcy Wentworth Thompson's science of form. Science in Context, 27(1), 79–107. Gliboff, S. (2015). Breeding better peas, pumpkins, and peasants: The practical mendelism of erich tschermak. In D. Phillips, & S. E. Kingsland (Eds.). New perspectives on the history of life sciences and agriculture (pp. 419–439). New York: Springer-Verlag. Gould, S. J. (1971). D'Arcy Thompson and the science of form. New Literary History, 2(2), 229–258. Gould, S. J. (2002). The structure of evolutionary theory. Cambridge: Harvard University Press. Jarron, M. (2013). Editorial. Interdisciplinary Science Reviews, 38(1), 1–11. Keller, E. F. (2002). Making sense of life: Explaining biological development with models, metaphors, and machines. Cambridge: Harvard University Press. Maartens, A. (2017). On Growth and form in context – an interview with matthew jarron. Development, 144(23), 4199–4202. Miall, L. C. (1892). The surface-film of water, and its relation to the life of plants and animals. Nature, 46(1175), 7–11. Ridley, M. (1986). Embryology and classical zoology in great Britain. In T. Horder, J.
8