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The Hubble-van Maanen conflict over internal motions in spiral nebulæ: yet more new information on an already old topic
V/stas/n Astronomy, Vol. 34, pp. 415-423, 1991 Printed in Gt'eat Britain. All rights reu~ved.
0083--6656/91 $0.{30+ .50 O 1992 Pergamon Preu pie.
THE HUBBLE-VAN MAANEN CONFLICT OVER INTERNAL MOTIONS IN SPIRAL NEBUL,'E: YET MORE NEW INFORMATION ON AN ALREADY OLD TOPIC Ronald W. Brashear* and Norriss S. Hetheringtont *Assistant Curator of Science Manuscripts, Huntington Library, 1151 Oxford Road, San Marino, CA 91108, U.S.A. i'Research Associate, Office for the History of Science and Technology, 470 Stepbens Hall, University of California, Berkeley, CA 94720, U.S.A.
Much has been written regarding Adriaan van Maanen's purported measurements of motions in spiral nebulae beginning in 1915, the contradiction thus posed in the early 1920s to belief in spirals as island universes, the ensuing controversy enduring into the 1930s, and possible causes of the error [Ref. 1]. Indeed, more has been written than a rational allocation of words to topics might have allowed. Such is, for better or worse, the nature of historical scholarship: some topics enjoy a continuing dialogue and advancing knowledge while others wait for their time in the sun. With these words of apology, we introduce yet more discoveries bearing upon the controversy over motions in spiral nebulae, these from the Mount Wilson Observatory Archives, which are just now being opened to scholars. One of the newly-available items consists of 172 large sheets of paper, some written on both sides, by Frederick H. Scares, editor of publications at the Mount Wilson Observatory. Much of this is numbers, measures by several astronomers at Mount Wilson of motions in spiral nebulae. More immediately understandable are three pages of notes in which Scares compares manuscripts written by Edwin Hubble, van Maanen's principal antagonist, and by himself [Ref. 2]. In one instance compared, Scares noted that Hubble had written on Page 10 of his manuscript ``conclusive evidence against reality of internal motions of order predicted," while Scares had written on Page 14 of his manuscript "definitely negative results." In another instance, Hubble had written on Page 17 ``highly improbable that systematic motions ... of order announced by vM should not be perceptible," while Scares found the evidence too weak to justify the phrase "highly improbable." 415
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These were, however, "the only cases (2) in which H ' s statement appreciably stronger than m i n e , " Scares noted, citing H u b b l e ' s conclusion (on Page 29 o f H u b b l e ' s manuscrip0 and his own conclusion (Page 37 o f Seares' manuscrip0. Clearly Seares made a considerable effort to produce a statement settling the controversy o v e r internal motions in spiral nebulm. And clearly Scares' conclusion differed little from H u b b l e ' s , though his wording might have been more temperate.
Discovery o f Scares' lost manuscript might provide
more information on the remeasurements at Mount Wilson, but is unlikely to alter the broad outlines o f the story. Another newly-available archival item is a twelve-page, typed, double-spaced, confidential m e m o r a n d u m , the first four pages o f which are devoted to the problem posed by the conflicting results o f Hubble and van Maanen [Ref. 3]. The document, written by Walter S. Adams, the Mount Wilson Observatory director, is dated 15 August 1935. It is addressed to John C. M e r r i a m , president o f the Carnegie Institution o f Washington, the observatory's financial patron. Officially, the observatory was a research department o f the institution. Though extraordinary in nature, A d a m s ' m e m o r a n d u m was in response to a routine request for information on recent and current activities o f the observatory, for use by M e r r i a m in his annual report [Ref. 4]. Adams began: Among the problems with which the observatory has had to deal during the year one of the most difficult has been that connected with the conflicting results obtained by van Maanen and Hubble for the motions in spiral nebulae. The situation has been complicated by a considerable amount of personal feeling between the two men. A brief history of the whole investigation is as follows. In 1915, at the suggestion of Dr. Hale, van Meanen undertook measurements of one or two of the larger spirals on photographs separated by intervals of about five or six years for the purpose of testing the possibility of relative motion within these objects. The earlier photographs were made by Ritchey soon after the 60-inch telescope was completed and were not made primarily with quantitative measures in mind. The results which van Maanen obtained were very consistent in indicating internal motions in these nebulae, more especially a component showing a movement of rotation for the points in the spiral arms. The investigation was continued by van Maanen during the following years and additional evidence for the motion of rotation was obtained from four or five other spirals. His measurements were internally consistent and quite definite in character, and his wide experience in astrometric work gave his conclusions a high standing among astronomers. Some were inclined to doubt the possibility of such motions in view of their belief in the great distances of these nebulae but they could offer no explanation of van Maanen's results. In later years the work of Hubble and others provided very strong evidence of the immense distance, of these nebula, and van Maanen's motions became an outstanding discregmncy. Naturally Hubble wished to investigate the source of the difference and for this purpose desired to have access to the photographs which van Maanen had measured. When he consulted me upon the subject, I told him that the primary concern of the Observatory was simply to learn the truth in the matter and that of course it was desirable that these photographs should be measured by other observers. I asked him, however, to consult van Maanen on the subject and to attempt to work with him on the solution of the problem. Due to the attitude and temperaments of both men there was no cooperation in the matter but much feeling developed. Hubble finally measured some of the plates and at his request and mine a few were also measured by Nicholson and Baade. Their results were essentially negative in character and mainly opposed to van Maanen's conclusions.
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New plates were desirable to extend the time interval of the measurements. It may also have been that lack of cooperation necessitated taking more plates than otherwise would have been required. Hubble was able to measure one early plate of M 33 (6 August 1910) and two plates each of M 51 (7 February 1910 and 8 April 1910), of M 81 (4 February 1910 and 21 March 1917), and of M 101 (10 March 1910 and 15 May 1915), all taken by George Willis Ritchey. Four of these plates had been included in van Maanen's measurements. The new plates were two of M 33 (14 September 1931 and 18 September 1933, by Milton Humason and Walter Baade, respectively), two of M 51 (21 February 1933 and 26 March 1933, by Hubble), two of M 81 (17 March 1925 and 17 April 1932, by Hubble), and two of M 101 (17 March 1925 and 26 March 1933, by Hubble) [Ref. 5]. It was strategically intelligent to have Seth B. Nicholson participate in the new measures, because he had earlier measured some of van Maanen's plates and his measures had been cited by van Maanen as corroboration. While Nicholson's measures agreed with van Maanen's within the uncertainties of the material, they clearly did not "avoid any doubt as to the results," Hubble noted in a brief and unpublished critique. Hubble also judged van Maanen's reference to similar motions in M 51 by the Russian astronomer Sergey Konstantinovich Kostinsky to be "entirely misleading," and van Maanen's reference to the Dutch astronomer W. J. A. Schouten's "similar motions" implying corroborative evidence as indicating "an uncritical imagination." [Ref. 6] Such was Hubble's attitude and temperament regarding van Maanen's work, though his language was more moderate in his later, long, unpublished manuscript than in his earlier, brief critique. Perhaps Adams' and Scares' guidance help explain the difference. Current readers, knowing that Hubble was fight and van Maanen was wrong, might well accept without demur the language in Hubble's uncompromising critique. Adams, however, in the midst of a controversy between two roughly equal members of his staff and without the advantage of historical hindsight, was not satisfied. He stated in his memorandum to Merriam: Hubble then wrote a long statement for publicationwhich both Scares and I felt could not be published in the form in which it was written. Its languagewas intemperatein many places and the attitude of animosity was marked. He objected to any material change in the wording and a deadlock seemed to be indicated. I then suggested that Seares discuss all of the measures and write a statement which should be submitted both to van Maanen and Hubble and not to be published without their consent. This was agreed to and Seares undertook a long and careful analysis of the ~ and prepared an accurate statementof the results. Thiswas to be publishedunder the namesof van Maanen, Hubble, Nicholson and Baade. The paper was submitted to those concerned and all agreed to its publication with minor changes with the exceptionof Hubble who opposed it violently. ! do not feel that Hubble's attitude in this matter was in any way justified. The situation then became very difficult. It was most desirablethat the new measures showing little or no evidence of rotational motion among the nebulaebe published promptly but in a thoroughly dispassionate and dignified way. I had many conferences with Hubble and he finally agreed to the publicationof a brief statementby himselfof the results of the new measures together with another short statement by van Maanencommentingupon possiblesources of error in his earlier measures. These two communicationsappeared in the May number of The Astrophysical Journal. This solution of the problem represented • compromisewhich was not thoroughly satisfactory but which at least presented the results without any violentlycontroversialfeatures. The attitude of van Maanen in the matter was much superior to that of Hubble: van Maanen, who fully believes in the existenceof the motions indicatedby his measures, went far in acknowledgingthe probable existenceof systematic errors; while Hubble, who had much the better of the general weight of evidence, showed • distinctly ungenerous and almost vindictive spirit. This is not the first case in which Hubble has
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seriously injured himself in the opinion of scientific mea by the intemperate gad intolerant way in which he has expressed himself. Of the technical aspects of this problem it is probably not too much to say that the balance of evidence is strongly in favor of the non-existence of such motions as van Maane.n thought he had found. The displacements he measured very probably existed on the plates but may have arisea from the quality of the images, particularly on the earlier photographs. The quantities measured at the time were very minute. I am glad that the whole question has been brought out into the open and that the Observatory can show that its concern is wholly with the final truth of the results.
For the second time, Adams states that the observatory's primary concern is to learn the truth. Perhaps he doth protest too much. Avoidance of public controversy and preservation of dignity also were important concerns -- as they would be for many an administrator, then and now. Much other evidence documents the high value that some astronomers placed upon working out disagreements privately. For example, Scares wrote to Harlow Shapley at Harvard with some criticisms, and Shapley replied "I appreciate your thoughtfulness in writing to me personally rather than replying publicly" [Ref. 7]. Adams apparently believed that van Maanen was an innocent victim of instrumental error. Cogent argument in several of Hubble's unpublished manuscripts on the possibility of a magnitude error, however, shows that no random error can explain van Maanen's purported detection of motions consistently in the same direction (unwinding) with respect not to photographic plates but with respect to the orientation of the arms of spiral nebula'. If van Maanen was an innocent victim, he was victimized not by instrumental error but rather by expectation; he found what he expected to find even though it did not exist. Adams finished the section of his memorandum on the Hubble-van Maanen controversy on a high note: I have described this episode in considerable detail since it has to do with two important members of the staff and has had reactions upon several others. It is, I am glad to say, the only case in which the members o f the staff have failed to show the most friendly and active cooperation in their fields of work.
Hubble's disdain for van Maanen's presentation, especially the claim of corroborative evidence, has been known for some years. Material newly available indicates that van Maanen's confidence in his own results remained strong, as Adams noted in his memorandum to Merriam, stronger than otherwise suggested in van Maanen's published note in the May 1935 issue of the Astrophysical Journal. Indeed, the concessionary phrases in that brief communication are now seen to have been dictated by Adams. The year started off well for van Maanen, with a letter from Kostinsky [Ref. 8]. The Russian astronomer had continued his photographic observations of M 51 begun in 1896, though the climate was not favorable at the Pulkova Observatory, near Leningrad, and the number of his observations was consequently not large. Still, from plates now taken over a period of 38 years, Kostinsky stated that he continued to find displacements in nebular knots (noeuds de la n~uleuse). He did not, however, furnish van Maanen with any quantitative data. In this respect, Kostinsky's letter was no more specific
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nor more persuasive than his 1917 paper [Ref. 9]. Nonetheless, van Maanen passed the letter on to Hale with the comment: "In the present controversy, I thought you might like to read this note from
Kostlnsky." Soon van Maanen was at work on a note of his own. Extant are a hand-written dra/~, a typed version, and the publication itself [Ref. 10]. The typed and printed versions do not differ significantly. The hand-written draft, however, is quite different in character. Van Maanen began, in both the draft and in the final, printed version, by acknowledging that in measuring motions in spiral nebulae he had always been aware of the possibility of systematic errors, especially because of the lengthy exposure of plates taken at the 25-foot focus of the 60-inch reflector and the considerable hour angles involved. Only in the printed note does van Maanen also mention as possible sources of error the choice of comparison stars brighter than the nebular knots and far from the center of the plates, and differential coma; presumably this caveat was added in response to Hubble's suggestion, thoroughly explored in unpublished manuscripts and ultimately abandoned, of a possible magnitude error. Because of the possibility of errors, "it was planned to wait with further work in this line until some plates taken at the 100" (sic) reflector with considerable shorter exposures (about one hour) .... " van Maanen wrote in the draft. The new plates would be taken at practically the same hour angles as the old plates had been. The printed note, in contrast to the hand-written draft, does not single out exposure time for emphasis among the possible sources of error. The hand-written draft ends with no suggestion that the remeasurements did anything but substantiate van Maanen's earlier purported results. For M 33 and M 74, van Maanen using the 100inch telescope found displacements in the same direction as before, 0.-013 ± 7?.7 [Ref. 5] and 0.-008 ± 0:001 [Ref. 5]. Furthermore, using the 80-foot focus of the 60-inch reflector, he obtained displacements of 0.-009 + 777 for M 33 and 0.'013 ± 0.-003 for M 101, both motions in the same direction as before. And Waiter Baade measured mean results of 0,,013 + 0.-006, with considerably higher dispersion but again in the same direction. Nicholson's measures on M 101 were, admittedly, considerably smaller than van Maa en's; van Maanen noted here in the hand-written draft another instance in which Nicholson's results were 33% larger than van Maanen's corresponding values, as if this fact somehow mitigated the discrepancy presented by the now smaller measures. There was no mention of Hubble's measurements, and the draft ended with no suggestion that the remeasurements did anything but substantiate van Maanen's earlier purported results. At this point in the controversy, Adams seems to have intervened. A one-page note in his handwriting reads [Ref. 11]: The results of the measures of Hubble, Bude and Nicholson together with my own measures of • few spiral nebulm on photographs taken during recent years make it highly probable that the early values obtained from the negatives taken at the 25-foot focus of the 60-inch reflector are subject to considzcable systematic errors. The long exposure times and the large hour angles which characterize many of the earlier photographs are serious drawbec,ks in an investigation requiring ~ u r a t e
messuremmts of both nebular points and comlmison ran. The more recent photogrg~ are much preferablein both of theserespects,and at preeeetnegativesplannedfor this investigtfionare being made J~VA 34:4-D
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with exposures of about one hour with the lO0-inch reflector, both the older and newer plates being of the same photographic quality and taken at nearly the same hour angle. Although my measures of recent plates with the stereocomparatorshow considerably smaller values of the apparent rotational componentthan those first obtained, the persistenceof the positivesign is very marked and requires the most searching investigation. Adams was not reporting measures of his own, but was suggesting, with some authority, what van Maanen should write. In his printed note, van Maanen follows immediately his statement that the measured motions are still in the same direction with an admission that the value for M 33 is considerably smaller than those found before. Van Maanen also added a new concluding paragraph for his printed note. First, he acknowledges the measures of Hubble, Baade, and Nicholson as among the factors that "make it desirable to view the motions with reserve." Then follows, with only minor changes, Adams' second paragraph. A final sentence in van Maanen's printed concluding paragraph notes that more "photographs are being taken with the 100-inch telescope possible under conditions which may avoid some of the possible systematic influences mentioned at the beginning of this note." The import of van Maanen's draft had been turned on its head. Rather than a persisting belief in the existence of the purported motions, van Maanen in the printed note conceded serious doubts. His willingness to compromise won Adams' admiration, while Hubble's insistence on following the evidence was perceived by Adams as both ungenerous and vindictive. For some years now, further study of this controversy has held promise of enlivening and illuminating sociological studies of science. Materials just now becoming available may well prove to be of considerable interest and over an extended time. Another discovery bearing upon the controversy over motions in spiral nebulae is mentioned here with embarrassment than with exuberance. It turns out that some material just now discovered in the newly-opened Mount Wilson Observatory Archives has been available elsewhere for more than two decades, in the microfilm edition of the George Ellery Hale papers [Ref. 12]. Van Maanen had undertaken his measurements in 1915 at the suggestion of Hale (then the director of the observatory), as Adams explained in his memorandum to Merriam. Hale's interest in the problem was stimulated by the American geologist Thomas C. Chamberlin, and there is considerable correspondence between Hale and Chamberlin, both preceding van Maanen's measurements and after the measurements, discussing their interpretation [Ref. 13]. "Better late than never" seems the most appropriate cliche to dredge up shamefacedly here. Also in order is an exculpatory promise to produce a research paper soon on Chamberlin, his planetesimal hypothesis, and its effect on research at the Mount Wilson Observatory, particularly on problems encountered in converting a geological hypothesis into an astronomical research program.
Hubble--van Maanen Conflict
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This instance of neglecting readily-available research material while waiting for archives to open reminds us that however exciting and enjoyable the examination of archival material is, and however much it adds to our understanding, much of the history of astronomy remains so little developed that study of more-readily-available material still holds enormous potential for the advance of knowledge. Historical investigation can productively proceed as a dialogue or dialectic. Tentative positions are formed and questions raised based upon preliminary readings of published papers and microfilm collections. Questions are answered and positions modified by subsequent and more wideranging enquiries, including studies of not-easily-accessible archival material which has meaning in the context of preliminary historical theses. Would-be scholars without access to research treasures should not be deterred from initiating work on whatever material is at hand -- any more than they should ultimately be content with less than every scrap of existing information.
REFERENCES 1. Michael Hoskin persuaded Mrs. Hubble to grant access to the Edwin Hubble papers, announced their existence at the Pads 1968 International Congress for the History of Science, and commented perceptively on the Hubble-van Maanen controversy in ~Edwin Hubble and the Existence of External Galaxies~ in Acres X l f Congr~s International d'Histoire des Sciences, V (Pads: Albert Blanchard, 1971), pp. 49-53. See also Hosidn, M.A. 1982, Stellar Astronomy: Historical Studies (Chalfont St. Giles: Science History Publications). J. D. Fernie (1970) noted in "The Historical Quest for the Nature of the Spiral Nebulae," Publ.Astron.Soc. Pacific, 83, 1189-1230, that a magnitude error would not serve to explain van Maanen's purported detection of motion consistently in the same direction with respect to the orientation of the arms of spiral nebulae. A review of scientific literature appeared two years later in Hetherington, N.S. 1972, "Adriaan van Maanen and Internal Motions in Spiral Nebulae: A Historical Review, ~ Quart.Journ. Roy.Astron.Soc., 13, 25-39. An examination of manuscript sources appeared the next year in Richard Berendzen and Richard Hart 1973, "Adriaan van Maanen's Influence on the Island Universe Theory," Journ.Hist.Astron., 4, 46-56 and 73-98, and in Hart, R. 1973, Adriaan van Maanen's Influence on the Island Universe Theory (Ph.D. Dissertation, Boston University). This work is also presented in Berendzen, Hart, and Daniel Seeley 1976, Man Discovers the Universe (New York: Neale Watson Academic Publications). Hetherington, N.S. 1974, "Edwin Hubble on Adriaan van Maanen's Internal Motions in Spiral Nebulae," Isis, 65, 390-393 (Edwin Huhble's examination of a possible magnitude error is described). See also: Hetherington, N.S. 1974, "Edwin Hubble's Examination of Internal Motions in Spiral Nebulae, ~ Quart.Journ. Roy.Astron.Soc., 15, 392-418. Hetherington, N.S. 1974, "Addaan van Maanen on the Significance of Internal Motions in Spiral Nebulae, ~ Journ.Hist.Astron., 5, 52-53 (A difference between the draft of van Maanen's first paper on motions in spiral nebulae and the published version is described).
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Hetherington, N.S. 1975, ~The Simultaneous 'Discovery' of Internal Motions in Spiral Nebulae," ibid., 6, 115-35 (Expectations of finding rotation are discussed). Hetherington, N.S. 1976, "Additional Shapley -- van Maanen Correspondence," ibid., 7, 7374 (More archival material is mentioned). Robert W. Smith explored efforts at the Mount Wilson Observatory to temper Hubble's criticism of van Maanen; see Smith, R.W. 1982, The Expanding Universe: Astronomy's Great Debate (Cambridge: Cambridge University Press). The topic is placed in a wider context in Hetherington 1983, ~Just How Objective is Science?," Nature, 306, 727-730; and in 1988, Science and Objectivity: Episodes in the History of Astronomy (Ames, Iowa: Iowa State University Press). I-Iubble's manuscripts are presented in full in I-Ietherington, N.S., ed. 1990, The Edwin Hubble Papers: Previously Unpublished Manuscripts on the Extragalactic Nature of Spiral Nebul~ (annotated, and with an Historical Introduction by Norriss S. Hetherington; Tucson, Arizona: Pachart Publishing House). 2. Frederick Hanley Seares Papers, Box 20, Mount Wilson Observatory Archives, Henry E. Huntington Library, San Marino California. The Hubble manuscript from which Seares quotes is evidently Hubble's typed, 33-page ~Intemal Motions of Spiral Nebulae," catalogued as HUB 35 A (the revised version), B (the earlier version), and C and D (partial carbon copies of A), Edwin Hubble Collection, Huntington Library. See "Edwin Hubble's Examination of Internal Motions in Spiral Nebulae* and The Edwin Hubble Papers ... (Reference 1). The Scares manuscript is yet to be found. 3. Walter S. Adams, "Mount Wilson Observatory Confidential Statement for President Merriam," twelve-page, typed, double-spaced memorandum, Adams Papers, Box 43, Mount Wilson Observatory Archives, Huntington Library. 4. W. M. Gilbert to Walter S. Adams, 28 May 1935, Adams Papers, Box 20. Gilbert was administrative secretary to John C. Merriam, president of the Carnegie Institution of Washington. Adams had left on 18 May for the International Astronomical Union meeting in Paris and did not return until around 12 August; hence the delay in his reply, though Seares had forwarded a copy of the letter. 5. Edwin Hubhle, "Internal Motions of Spiral Nebula" [Reference 1]. 6. Edwin Hubhle, untitled and undated three-page typescript on van Maanen's corroborative evidence, (probably written between 1923 and 1925, citing as it does a 1923 paper and not mentioning a relevant and easily accessible 1925 paper), HUB 69, Hubble Collection. The manuscript has been discussed in "Edwin Hubble's Examination of Intemai Motions in Spiral Nebul~e" and is available in The Edwin Hubble Papers ... [Reference 1]. 7. Frederick Seares to Harlow Shapley, 4 May 1925, and Simple), to Seares, 12 May 1925, Seares Papers, Box 15 [Reference 2].
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8. S. Kosfinsky to A. van Maanen, 31 December 1934, Adriaan van Maanen Papers, Mount Wilson Observatory Archives, Huntington Library. 9. S. Kostinsky, S. 1917, "Probable Motions in the Spiral Nebula Messier 51 (Canes Venatici) found with the Stereo-Comparator. Preliminary Communication," Monthly Notices Roy.Astron.Soc., 77, 233-234. The paper also appeared in the Bulletin of the Russian Imperial Academy of Sciences in 1916, pp. 871-873. 10. van Maanen, A. 1935, ~The Internal Motions in Spiral Nebulae," three-page, un-dated, handwritten manuscript, and ~Internal Motion in Spiral Nebulae," two-page, typed, undated draft, van Maanen Papers; van Maanen, A. 1935, *Internal Motions in Spiral Nebulz," Astrophys.J., 81, 336-337. This note immediately followed one by Edwin Hubble, ~Angular Rotation of Spiral Nebulae," ibid., 334-335. 11. One-page, untitled, undated, note in the hand of W. S. Adams, van Maanen Papers. 12. Daniel J. Kevles, ed., George Ellery Hale Papers, 1882-1937 (Washington, D.C.: Carnegie Institution of Washington, 1967, Pasadena: California Institute of Technology, 1968), microfilm edition. 13. On Chamberlin, see Stephen G. Brush, "A Geologist among Astronomers: The Rise and Fall of the Chamberlin-Moulton Cosmogony," Journ.Hist.Astron., 9 (1978), pp. 1-41 and pp. 77-104.
0083--6656/91 $0.{30+ .50 O 1992 Pergamon Preu pie.
THE HUBBLE-VAN MAANEN CONFLICT OVER INTERNAL MOTIONS IN SPIRAL NEBUL,'E: YET MORE NEW INFORMATION ON AN ALREADY OLD TOPIC Ronald W. Brashear* and Norriss S. Hetheringtont *Assistant Curator of Science Manuscripts, Huntington Library, 1151 Oxford Road, San Marino, CA 91108, U.S.A. i'Research Associate, Office for the History of Science and Technology, 470 Stepbens Hall, University of California, Berkeley, CA 94720, U.S.A.
Much has been written regarding Adriaan van Maanen's purported measurements of motions in spiral nebulae beginning in 1915, the contradiction thus posed in the early 1920s to belief in spirals as island universes, the ensuing controversy enduring into the 1930s, and possible causes of the error [Ref. 1]. Indeed, more has been written than a rational allocation of words to topics might have allowed. Such is, for better or worse, the nature of historical scholarship: some topics enjoy a continuing dialogue and advancing knowledge while others wait for their time in the sun. With these words of apology, we introduce yet more discoveries bearing upon the controversy over motions in spiral nebulae, these from the Mount Wilson Observatory Archives, which are just now being opened to scholars. One of the newly-available items consists of 172 large sheets of paper, some written on both sides, by Frederick H. Scares, editor of publications at the Mount Wilson Observatory. Much of this is numbers, measures by several astronomers at Mount Wilson of motions in spiral nebulae. More immediately understandable are three pages of notes in which Scares compares manuscripts written by Edwin Hubble, van Maanen's principal antagonist, and by himself [Ref. 2]. In one instance compared, Scares noted that Hubble had written on Page 10 of his manuscript ``conclusive evidence against reality of internal motions of order predicted," while Scares had written on Page 14 of his manuscript "definitely negative results." In another instance, Hubble had written on Page 17 ``highly improbable that systematic motions ... of order announced by vM should not be perceptible," while Scares found the evidence too weak to justify the phrase "highly improbable." 415
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These were, however, "the only cases (2) in which H ' s statement appreciably stronger than m i n e , " Scares noted, citing H u b b l e ' s conclusion (on Page 29 o f H u b b l e ' s manuscrip0 and his own conclusion (Page 37 o f Seares' manuscrip0. Clearly Seares made a considerable effort to produce a statement settling the controversy o v e r internal motions in spiral nebulm. And clearly Scares' conclusion differed little from H u b b l e ' s , though his wording might have been more temperate.
Discovery o f Scares' lost manuscript might provide
more information on the remeasurements at Mount Wilson, but is unlikely to alter the broad outlines o f the story. Another newly-available archival item is a twelve-page, typed, double-spaced, confidential m e m o r a n d u m , the first four pages o f which are devoted to the problem posed by the conflicting results o f Hubble and van Maanen [Ref. 3]. The document, written by Walter S. Adams, the Mount Wilson Observatory director, is dated 15 August 1935. It is addressed to John C. M e r r i a m , president o f the Carnegie Institution o f Washington, the observatory's financial patron. Officially, the observatory was a research department o f the institution. Though extraordinary in nature, A d a m s ' m e m o r a n d u m was in response to a routine request for information on recent and current activities o f the observatory, for use by M e r r i a m in his annual report [Ref. 4]. Adams began: Among the problems with which the observatory has had to deal during the year one of the most difficult has been that connected with the conflicting results obtained by van Maanen and Hubble for the motions in spiral nebulae. The situation has been complicated by a considerable amount of personal feeling between the two men. A brief history of the whole investigation is as follows. In 1915, at the suggestion of Dr. Hale, van Meanen undertook measurements of one or two of the larger spirals on photographs separated by intervals of about five or six years for the purpose of testing the possibility of relative motion within these objects. The earlier photographs were made by Ritchey soon after the 60-inch telescope was completed and were not made primarily with quantitative measures in mind. The results which van Maanen obtained were very consistent in indicating internal motions in these nebulae, more especially a component showing a movement of rotation for the points in the spiral arms. The investigation was continued by van Maanen during the following years and additional evidence for the motion of rotation was obtained from four or five other spirals. His measurements were internally consistent and quite definite in character, and his wide experience in astrometric work gave his conclusions a high standing among astronomers. Some were inclined to doubt the possibility of such motions in view of their belief in the great distances of these nebulae but they could offer no explanation of van Maanen's results. In later years the work of Hubble and others provided very strong evidence of the immense distance, of these nebula, and van Maanen's motions became an outstanding discregmncy. Naturally Hubble wished to investigate the source of the difference and for this purpose desired to have access to the photographs which van Maanen had measured. When he consulted me upon the subject, I told him that the primary concern of the Observatory was simply to learn the truth in the matter and that of course it was desirable that these photographs should be measured by other observers. I asked him, however, to consult van Maanen on the subject and to attempt to work with him on the solution of the problem. Due to the attitude and temperaments of both men there was no cooperation in the matter but much feeling developed. Hubble finally measured some of the plates and at his request and mine a few were also measured by Nicholson and Baade. Their results were essentially negative in character and mainly opposed to van Maanen's conclusions.
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New plates were desirable to extend the time interval of the measurements. It may also have been that lack of cooperation necessitated taking more plates than otherwise would have been required. Hubble was able to measure one early plate of M 33 (6 August 1910) and two plates each of M 51 (7 February 1910 and 8 April 1910), of M 81 (4 February 1910 and 21 March 1917), and of M 101 (10 March 1910 and 15 May 1915), all taken by George Willis Ritchey. Four of these plates had been included in van Maanen's measurements. The new plates were two of M 33 (14 September 1931 and 18 September 1933, by Milton Humason and Walter Baade, respectively), two of M 51 (21 February 1933 and 26 March 1933, by Hubble), two of M 81 (17 March 1925 and 17 April 1932, by Hubble), and two of M 101 (17 March 1925 and 26 March 1933, by Hubble) [Ref. 5]. It was strategically intelligent to have Seth B. Nicholson participate in the new measures, because he had earlier measured some of van Maanen's plates and his measures had been cited by van Maanen as corroboration. While Nicholson's measures agreed with van Maanen's within the uncertainties of the material, they clearly did not "avoid any doubt as to the results," Hubble noted in a brief and unpublished critique. Hubble also judged van Maanen's reference to similar motions in M 51 by the Russian astronomer Sergey Konstantinovich Kostinsky to be "entirely misleading," and van Maanen's reference to the Dutch astronomer W. J. A. Schouten's "similar motions" implying corroborative evidence as indicating "an uncritical imagination." [Ref. 6] Such was Hubble's attitude and temperament regarding van Maanen's work, though his language was more moderate in his later, long, unpublished manuscript than in his earlier, brief critique. Perhaps Adams' and Scares' guidance help explain the difference. Current readers, knowing that Hubble was fight and van Maanen was wrong, might well accept without demur the language in Hubble's uncompromising critique. Adams, however, in the midst of a controversy between two roughly equal members of his staff and without the advantage of historical hindsight, was not satisfied. He stated in his memorandum to Merriam: Hubble then wrote a long statement for publicationwhich both Scares and I felt could not be published in the form in which it was written. Its languagewas intemperatein many places and the attitude of animosity was marked. He objected to any material change in the wording and a deadlock seemed to be indicated. I then suggested that Seares discuss all of the measures and write a statement which should be submitted both to van Maanen and Hubble and not to be published without their consent. This was agreed to and Seares undertook a long and careful analysis of the ~ and prepared an accurate statementof the results. Thiswas to be publishedunder the namesof van Maanen, Hubble, Nicholson and Baade. The paper was submitted to those concerned and all agreed to its publication with minor changes with the exceptionof Hubble who opposed it violently. ! do not feel that Hubble's attitude in this matter was in any way justified. The situation then became very difficult. It was most desirablethat the new measures showing little or no evidence of rotational motion among the nebulaebe published promptly but in a thoroughly dispassionate and dignified way. I had many conferences with Hubble and he finally agreed to the publicationof a brief statementby himselfof the results of the new measures together with another short statement by van Maanencommentingupon possiblesources of error in his earlier measures. These two communicationsappeared in the May number of The Astrophysical Journal. This solution of the problem represented • compromisewhich was not thoroughly satisfactory but which at least presented the results without any violentlycontroversialfeatures. The attitude of van Maanen in the matter was much superior to that of Hubble: van Maanen, who fully believes in the existenceof the motions indicatedby his measures, went far in acknowledgingthe probable existenceof systematic errors; while Hubble, who had much the better of the general weight of evidence, showed • distinctly ungenerous and almost vindictive spirit. This is not the first case in which Hubble has
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seriously injured himself in the opinion of scientific mea by the intemperate gad intolerant way in which he has expressed himself. Of the technical aspects of this problem it is probably not too much to say that the balance of evidence is strongly in favor of the non-existence of such motions as van Maane.n thought he had found. The displacements he measured very probably existed on the plates but may have arisea from the quality of the images, particularly on the earlier photographs. The quantities measured at the time were very minute. I am glad that the whole question has been brought out into the open and that the Observatory can show that its concern is wholly with the final truth of the results.
For the second time, Adams states that the observatory's primary concern is to learn the truth. Perhaps he doth protest too much. Avoidance of public controversy and preservation of dignity also were important concerns -- as they would be for many an administrator, then and now. Much other evidence documents the high value that some astronomers placed upon working out disagreements privately. For example, Scares wrote to Harlow Shapley at Harvard with some criticisms, and Shapley replied "I appreciate your thoughtfulness in writing to me personally rather than replying publicly" [Ref. 7]. Adams apparently believed that van Maanen was an innocent victim of instrumental error. Cogent argument in several of Hubble's unpublished manuscripts on the possibility of a magnitude error, however, shows that no random error can explain van Maanen's purported detection of motions consistently in the same direction (unwinding) with respect not to photographic plates but with respect to the orientation of the arms of spiral nebula'. If van Maanen was an innocent victim, he was victimized not by instrumental error but rather by expectation; he found what he expected to find even though it did not exist. Adams finished the section of his memorandum on the Hubble-van Maanen controversy on a high note: I have described this episode in considerable detail since it has to do with two important members of the staff and has had reactions upon several others. It is, I am glad to say, the only case in which the members o f the staff have failed to show the most friendly and active cooperation in their fields of work.
Hubble's disdain for van Maanen's presentation, especially the claim of corroborative evidence, has been known for some years. Material newly available indicates that van Maanen's confidence in his own results remained strong, as Adams noted in his memorandum to Merriam, stronger than otherwise suggested in van Maanen's published note in the May 1935 issue of the Astrophysical Journal. Indeed, the concessionary phrases in that brief communication are now seen to have been dictated by Adams. The year started off well for van Maanen, with a letter from Kostinsky [Ref. 8]. The Russian astronomer had continued his photographic observations of M 51 begun in 1896, though the climate was not favorable at the Pulkova Observatory, near Leningrad, and the number of his observations was consequently not large. Still, from plates now taken over a period of 38 years, Kostinsky stated that he continued to find displacements in nebular knots (noeuds de la n~uleuse). He did not, however, furnish van Maanen with any quantitative data. In this respect, Kostinsky's letter was no more specific
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nor more persuasive than his 1917 paper [Ref. 9]. Nonetheless, van Maanen passed the letter on to Hale with the comment: "In the present controversy, I thought you might like to read this note from
Kostlnsky." Soon van Maanen was at work on a note of his own. Extant are a hand-written dra/~, a typed version, and the publication itself [Ref. 10]. The typed and printed versions do not differ significantly. The hand-written draft, however, is quite different in character. Van Maanen began, in both the draft and in the final, printed version, by acknowledging that in measuring motions in spiral nebulae he had always been aware of the possibility of systematic errors, especially because of the lengthy exposure of plates taken at the 25-foot focus of the 60-inch reflector and the considerable hour angles involved. Only in the printed note does van Maanen also mention as possible sources of error the choice of comparison stars brighter than the nebular knots and far from the center of the plates, and differential coma; presumably this caveat was added in response to Hubble's suggestion, thoroughly explored in unpublished manuscripts and ultimately abandoned, of a possible magnitude error. Because of the possibility of errors, "it was planned to wait with further work in this line until some plates taken at the 100" (sic) reflector with considerable shorter exposures (about one hour) .... " van Maanen wrote in the draft. The new plates would be taken at practically the same hour angles as the old plates had been. The printed note, in contrast to the hand-written draft, does not single out exposure time for emphasis among the possible sources of error. The hand-written draft ends with no suggestion that the remeasurements did anything but substantiate van Maanen's earlier purported results. For M 33 and M 74, van Maanen using the 100inch telescope found displacements in the same direction as before, 0.-013 ± 7?.7 [Ref. 5] and 0.-008 ± 0:001 [Ref. 5]. Furthermore, using the 80-foot focus of the 60-inch reflector, he obtained displacements of 0.-009 + 777 for M 33 and 0.'013 ± 0.-003 for M 101, both motions in the same direction as before. And Waiter Baade measured mean results of 0,,013 + 0.-006, with considerably higher dispersion but again in the same direction. Nicholson's measures on M 101 were, admittedly, considerably smaller than van Maa en's; van Maanen noted here in the hand-written draft another instance in which Nicholson's results were 33% larger than van Maanen's corresponding values, as if this fact somehow mitigated the discrepancy presented by the now smaller measures. There was no mention of Hubble's measurements, and the draft ended with no suggestion that the remeasurements did anything but substantiate van Maanen's earlier purported results. At this point in the controversy, Adams seems to have intervened. A one-page note in his handwriting reads [Ref. 11]: The results of the measures of Hubble, Bude and Nicholson together with my own measures of • few spiral nebulm on photographs taken during recent years make it highly probable that the early values obtained from the negatives taken at the 25-foot focus of the 60-inch reflector are subject to considzcable systematic errors. The long exposure times and the large hour angles which characterize many of the earlier photographs are serious drawbec,ks in an investigation requiring ~ u r a t e
messuremmts of both nebular points and comlmison ran. The more recent photogrg~ are much preferablein both of theserespects,and at preeeetnegativesplannedfor this investigtfionare being made J~VA 34:4-D
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with exposures of about one hour with the lO0-inch reflector, both the older and newer plates being of the same photographic quality and taken at nearly the same hour angle. Although my measures of recent plates with the stereocomparatorshow considerably smaller values of the apparent rotational componentthan those first obtained, the persistenceof the positivesign is very marked and requires the most searching investigation. Adams was not reporting measures of his own, but was suggesting, with some authority, what van Maanen should write. In his printed note, van Maanen follows immediately his statement that the measured motions are still in the same direction with an admission that the value for M 33 is considerably smaller than those found before. Van Maanen also added a new concluding paragraph for his printed note. First, he acknowledges the measures of Hubble, Baade, and Nicholson as among the factors that "make it desirable to view the motions with reserve." Then follows, with only minor changes, Adams' second paragraph. A final sentence in van Maanen's printed concluding paragraph notes that more "photographs are being taken with the 100-inch telescope possible under conditions which may avoid some of the possible systematic influences mentioned at the beginning of this note." The import of van Maanen's draft had been turned on its head. Rather than a persisting belief in the existence of the purported motions, van Maanen in the printed note conceded serious doubts. His willingness to compromise won Adams' admiration, while Hubble's insistence on following the evidence was perceived by Adams as both ungenerous and vindictive. For some years now, further study of this controversy has held promise of enlivening and illuminating sociological studies of science. Materials just now becoming available may well prove to be of considerable interest and over an extended time. Another discovery bearing upon the controversy over motions in spiral nebulae is mentioned here with embarrassment than with exuberance. It turns out that some material just now discovered in the newly-opened Mount Wilson Observatory Archives has been available elsewhere for more than two decades, in the microfilm edition of the George Ellery Hale papers [Ref. 12]. Van Maanen had undertaken his measurements in 1915 at the suggestion of Hale (then the director of the observatory), as Adams explained in his memorandum to Merriam. Hale's interest in the problem was stimulated by the American geologist Thomas C. Chamberlin, and there is considerable correspondence between Hale and Chamberlin, both preceding van Maanen's measurements and after the measurements, discussing their interpretation [Ref. 13]. "Better late than never" seems the most appropriate cliche to dredge up shamefacedly here. Also in order is an exculpatory promise to produce a research paper soon on Chamberlin, his planetesimal hypothesis, and its effect on research at the Mount Wilson Observatory, particularly on problems encountered in converting a geological hypothesis into an astronomical research program.
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This instance of neglecting readily-available research material while waiting for archives to open reminds us that however exciting and enjoyable the examination of archival material is, and however much it adds to our understanding, much of the history of astronomy remains so little developed that study of more-readily-available material still holds enormous potential for the advance of knowledge. Historical investigation can productively proceed as a dialogue or dialectic. Tentative positions are formed and questions raised based upon preliminary readings of published papers and microfilm collections. Questions are answered and positions modified by subsequent and more wideranging enquiries, including studies of not-easily-accessible archival material which has meaning in the context of preliminary historical theses. Would-be scholars without access to research treasures should not be deterred from initiating work on whatever material is at hand -- any more than they should ultimately be content with less than every scrap of existing information.
REFERENCES 1. Michael Hoskin persuaded Mrs. Hubble to grant access to the Edwin Hubble papers, announced their existence at the Pads 1968 International Congress for the History of Science, and commented perceptively on the Hubble-van Maanen controversy in ~Edwin Hubble and the Existence of External Galaxies~ in Acres X l f Congr~s International d'Histoire des Sciences, V (Pads: Albert Blanchard, 1971), pp. 49-53. See also Hosidn, M.A. 1982, Stellar Astronomy: Historical Studies (Chalfont St. Giles: Science History Publications). J. D. Fernie (1970) noted in "The Historical Quest for the Nature of the Spiral Nebulae," Publ.Astron.Soc. Pacific, 83, 1189-1230, that a magnitude error would not serve to explain van Maanen's purported detection of motion consistently in the same direction with respect to the orientation of the arms of spiral nebulae. A review of scientific literature appeared two years later in Hetherington, N.S. 1972, "Adriaan van Maanen and Internal Motions in Spiral Nebulae: A Historical Review, ~ Quart.Journ. Roy.Astron.Soc., 13, 25-39. An examination of manuscript sources appeared the next year in Richard Berendzen and Richard Hart 1973, "Adriaan van Maanen's Influence on the Island Universe Theory," Journ.Hist.Astron., 4, 46-56 and 73-98, and in Hart, R. 1973, Adriaan van Maanen's Influence on the Island Universe Theory (Ph.D. Dissertation, Boston University). This work is also presented in Berendzen, Hart, and Daniel Seeley 1976, Man Discovers the Universe (New York: Neale Watson Academic Publications). Hetherington, N.S. 1974, "Edwin Hubble on Adriaan van Maanen's Internal Motions in Spiral Nebulae," Isis, 65, 390-393 (Edwin Huhble's examination of a possible magnitude error is described). See also: Hetherington, N.S. 1974, "Edwin Hubble's Examination of Internal Motions in Spiral Nebulae, ~ Quart.Journ. Roy.Astron.Soc., 15, 392-418. Hetherington, N.S. 1974, "Addaan van Maanen on the Significance of Internal Motions in Spiral Nebulae, ~ Journ.Hist.Astron., 5, 52-53 (A difference between the draft of van Maanen's first paper on motions in spiral nebulae and the published version is described).
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Hetherington, N.S. 1975, ~The Simultaneous 'Discovery' of Internal Motions in Spiral Nebulae," ibid., 6, 115-35 (Expectations of finding rotation are discussed). Hetherington, N.S. 1976, "Additional Shapley -- van Maanen Correspondence," ibid., 7, 7374 (More archival material is mentioned). Robert W. Smith explored efforts at the Mount Wilson Observatory to temper Hubble's criticism of van Maanen; see Smith, R.W. 1982, The Expanding Universe: Astronomy's Great Debate (Cambridge: Cambridge University Press). The topic is placed in a wider context in Hetherington 1983, ~Just How Objective is Science?," Nature, 306, 727-730; and in 1988, Science and Objectivity: Episodes in the History of Astronomy (Ames, Iowa: Iowa State University Press). I-Iubble's manuscripts are presented in full in I-Ietherington, N.S., ed. 1990, The Edwin Hubble Papers: Previously Unpublished Manuscripts on the Extragalactic Nature of Spiral Nebul~ (annotated, and with an Historical Introduction by Norriss S. Hetherington; Tucson, Arizona: Pachart Publishing House). 2. Frederick Hanley Seares Papers, Box 20, Mount Wilson Observatory Archives, Henry E. Huntington Library, San Marino California. The Hubble manuscript from which Seares quotes is evidently Hubble's typed, 33-page ~Intemal Motions of Spiral Nebulae," catalogued as HUB 35 A (the revised version), B (the earlier version), and C and D (partial carbon copies of A), Edwin Hubble Collection, Huntington Library. See "Edwin Hubble's Examination of Internal Motions in Spiral Nebulae* and The Edwin Hubble Papers ... (Reference 1). The Scares manuscript is yet to be found. 3. Walter S. Adams, "Mount Wilson Observatory Confidential Statement for President Merriam," twelve-page, typed, double-spaced memorandum, Adams Papers, Box 43, Mount Wilson Observatory Archives, Huntington Library. 4. W. M. Gilbert to Walter S. Adams, 28 May 1935, Adams Papers, Box 20. Gilbert was administrative secretary to John C. Merriam, president of the Carnegie Institution of Washington. Adams had left on 18 May for the International Astronomical Union meeting in Paris and did not return until around 12 August; hence the delay in his reply, though Seares had forwarded a copy of the letter. 5. Edwin Hubhle, "Internal Motions of Spiral Nebula" [Reference 1]. 6. Edwin Hubhle, untitled and undated three-page typescript on van Maanen's corroborative evidence, (probably written between 1923 and 1925, citing as it does a 1923 paper and not mentioning a relevant and easily accessible 1925 paper), HUB 69, Hubble Collection. The manuscript has been discussed in "Edwin Hubble's Examination of Intemai Motions in Spiral Nebul~e" and is available in The Edwin Hubble Papers ... [Reference 1]. 7. Frederick Seares to Harlow Shapley, 4 May 1925, and Simple), to Seares, 12 May 1925, Seares Papers, Box 15 [Reference 2].
Hubble--vanMaanenConflict
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8. S. Kosfinsky to A. van Maanen, 31 December 1934, Adriaan van Maanen Papers, Mount Wilson Observatory Archives, Huntington Library. 9. S. Kostinsky, S. 1917, "Probable Motions in the Spiral Nebula Messier 51 (Canes Venatici) found with the Stereo-Comparator. Preliminary Communication," Monthly Notices Roy.Astron.Soc., 77, 233-234. The paper also appeared in the Bulletin of the Russian Imperial Academy of Sciences in 1916, pp. 871-873. 10. van Maanen, A. 1935, ~The Internal Motions in Spiral Nebulae," three-page, un-dated, handwritten manuscript, and ~Internal Motion in Spiral Nebulae," two-page, typed, undated draft, van Maanen Papers; van Maanen, A. 1935, *Internal Motions in Spiral Nebulz," Astrophys.J., 81, 336-337. This note immediately followed one by Edwin Hubble, ~Angular Rotation of Spiral Nebulae," ibid., 334-335. 11. One-page, untitled, undated, note in the hand of W. S. Adams, van Maanen Papers. 12. Daniel J. Kevles, ed., George Ellery Hale Papers, 1882-1937 (Washington, D.C.: Carnegie Institution of Washington, 1967, Pasadena: California Institute of Technology, 1968), microfilm edition. 13. On Chamberlin, see Stephen G. Brush, "A Geologist among Astronomers: The Rise and Fall of the Chamberlin-Moulton Cosmogony," Journ.Hist.Astron., 9 (1978), pp. 1-41 and pp. 77-104.