On the atmospheric influence of woods

JOURNAL OF T H E

FRANKLIN

INSTITUTE OF THE.

~tate of Deuu~l~a1~a; D E V O T E D TO T I t E lYIEOH~kNI0 AtlTS~ MA~UPAE~Tff11ES,

~EI~,RA

"r- S O I ~ I ~ O E ,

AND T H E ItE, C O I t D I N G OF

A~IERICAN AND O T H E R P A T E N T E D I N V E N T I O N S . O C T O B E R , 1829.

On the Jttmospheric lnfluence of Woods, [n~. e ects produced on ehmate, by the preservation or destruction of forests, is an interesting subject of inquiry, which has s o m e times engaged the attention not only of philosophers, but of legislators. In France, about forty years ago, some alarm was created, on account of the rapid cutting down of woods, which had then changed owners, or were less carefully protected than they had ibrmerly been. Where wood forms a great part of the fuel of a country., a strong motive will always exist for the planting Of trees, and lbr guarding against their wasteful removal. But another evi[~: than theddeficiency Ofvfirewood, was then apprel~ended.' • I t was ¢0n.,tende i by Cadet de aux, and other writers, thatthe great d r o u g ~ I experienced in some districts, were caused by the absenim o~Yt~: trees, which used to attract the clouds, and thus Conduct to the e a ~ those fertilizing showers, which reward the labours,ofthe husbandman ~ith an abundant harvest. Amidst the agitations of the revolution, the complaints of these writers were listened to, and their representations were more thai~ once brought under the consideration of the Convention, and the Council of Fi~e Hundred. We do not precisely recollect what legislative measures were adopted~ but we believe, among other things, the sale of the National Forests was stopped. However, it does not appear that what was then done, though it may have saved some of the property in the possession of the state, had any important eft'cot on the whole. Indeed, it will be seen from what fo!lows, that since that per~od, the woods of France have susVoL. I V . ~ N o . 4.--Oc','OB~, 1829. ~8

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On lhe Jllmosphevi¢ Influence o f tl/oods'.

rained a considerable diminution, equal in extent to the difference between 5 and ~2- of the territm'y. In the mean time, the investigation of this interesting subject h a s not beetl neglected. The affention of naturalists and men of science in the Netherlands, was, in the course of last )'ear: ca!ted to t h e alterations produced in the physical state of countries, ny the d e struction of forests, in consequence of a prize for the investigatior~ of this important question, being oil'ered by the Royal Philosophical Society of Brussels. The essay which obtained the prize, was w r i t ten in b~rench by M. A. Moreau de Jonnes, a staff-otiicer in t h e army. It appears that the author does not altog.e!ber concur with M. Cadet de Vaux ; but we have not seen tile ortgmal, and the foIlowing account has reference to a German translation, by M. Widenmann, Professor of Natural History, at Tubingen. In Germany, where ~reat importance is attached to the subject, the work of M . Moreat7 de Jonnes has been, upon the whole, very favourably noticed by the reviewers of that country, and we have taken the liberty to make use of some of their observations. The author begins with a statistical account of certain woods a n d forests, from which, though he complains of the insufficiency of the documents available tbr his calculation, at least one conclusion, which appears pretty welt founded, may be drawn. Accordin_~ to the data here made use of; the woods in France amounted, in 1~50~ to more than a tburth of the .surface of the whole country; in 17"88, to a seventh; and in 1814~ tO not quite a twelfth of that surface. Thus, within sixty-four years, 5000 square miles of the woods of France must have disappeared. In England, according to the author's estimate, the woods amount to only one twenty-third of the surface.

CHAP. I.~Influenee of Woods on the Temperature of Countries. Woods lower the temperature. In the author's opinion, they h a v e this effect, because, on account of their dark colour~ they reflect back few rays of light and heat to the atmosphere, and because t h e y keep the soil (lamp~ and, therefore, render more heat necessary to promote evaporation. But whether the diffhrence of the mean t e m perature between Rome and Massachusetts, which, in the same ~ e o graphical latitude, amounts to 6] cents of a degree, is to be attributed almost entirely to the woods, does not appear so easily demonstrable. That woods on mountains have a great influence in intercepting a n d beating down wlpours is very probable; but the author's assertion, that the increased condensation of vapours has for its consequence a greater absorption of heat, is unsupported by proof. It must a l s o be observed~ that though woods diminish temperature, and though the author proves this iact by practical observations~ yet the experiments as cited by him are so detached, as to leave room for considerable objection. Vienna and Troyes have not a diflhrence of temperature, merely because eastern countries are generally more covered with wood~ but also because the site of Vienna is ~50 feet hip/her, and lies nearer high mountains than Troyes. Again, Berlin is colder than Leyden in Holland~ not altogether in consequence of Brandeu-

0~ the ~qlmospherie hT,fluenee oar FVoods,

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burg being a woody country, but also because it is e ~ s e d ,to the coiu east wind. The translator points out tile difference 0f heigh~ which in the original is unattended to. The author shows fi'om historical 'comparisons, that the clearing away of woods makes the temperature of eounh:ies warmer. Wh~thcr the proofs that he adduces for tilt~ purpose are all quite convincing, we cannot positively affirm, tho%h the fact itself is true~ for France is no more deprived of its woods than England. If, then, there be, at present, nearly the same degree of heat in London and Paris, while, in the time of Tacitus, Gaul must have been colder, it is not quite clear why this contrary inttuence shouhl proceed from the same cause. But it is also doubtful whether Tacitus would not, even now, if he had no assistance from the thermometer, call London milder than Paris, because severe winters occur less often in the fi~rmer But thou-h tile details of these corn• titan in the latter cit patasons may o,zcasionally be uncertain, and more particularly those which relate to the question, whether a difference of temperature in former times ought to be attributed solely to the great abundance of woods and forests, yet a collection of the accounts of a greater degree of cold having heretofore existed, is doubtless very important. There can be but few to whom it will not be interesting to learn how much the cold of winter~ especially in the south of Europe~ has diminished. -

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CHAp. II.--lnJtuence on the quantity of Rain. The author here brings forward some observations to prove that more rain fails on the sea coast than in inland districts, and that, moreover, when chains of mountains run parallel to the sea-shore, the sides next the sea receive more rain than their opposite sides. In reference to woods, however, tile author supposes that he may lay it down as a fact confirmed by observation, that woodlands in fiat countries do not perceptibly increase the ~uantity of rain; but that woods on mountains have a perceptible innuence in producing.that efii~ct. He thereupon founds the conclusion, that if mountain~;a~e planted with trees, the quantity of rain in their vicinity will be ificreased, and that the progressive diminution of rain in thel s o ~ Eurone is to be ascribed to the destruction of :the mountain W ~ . Butt'he author does not appear to have been sufficiently 6ate(ut.ln ascertaining what are the places in which the rain has ~limlnish~l. It has not diminished in all parts of the south of Europe; for Flaugergues has found that the quantity of rain has considerably increased at ~/iviers, in the south of France, since 1778. The Milanese Ephemerides indicate the same thing for Milan, and all the assertior;s of this kind require further demonstration.

ChAr. III.--Of the Influence of Wood,s on the Humidity of the Jttmoslghere. Here the author describes~ among other things, an interesting experiment with the hygrometer, according to whieh tile humidity of the air in the West ladies is found to be expressed by the numbers

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On the d21mospherie Influence o f Woods.

$, 4, and 15, according as the observations are made on the coast in the midst of cultivated plantations, on the borders of mountain woods, or in the midst of those woods. There seems, however,, to be some obscurity in an observation wllich the author is induced to make, namely, that the humidity of woods in the torrid zone extends fat above tile extremity of the scale. Now, as the hy~/'ometer is usually graduated up to the point of complete humidity o! the atmosphere, it ~an only be said that the moisture is precipitated in greater abun. dance than is necessary to bring the hygrometer to the highest de. gree. W e cannot venture to quote any more of these observations, or to explain the grounds of the doubts to which the conclusions drawn by the author give rise. But notwithstanding these doubts, we confess with pleasure that much information is to be tbund in the work. At the same time; we must regret that the translator has not given to his version that great superiority over the original which it would have obtained had he subjected several of the author's statemen% such as those relative to the cmnparative humidity of the Mark of Brandenburg and Holland~ to critical investigation. CHAr. IV.--Influence of ~'oods on Springs and Running TVater. That countries, especially mountainous countries, which arc covered with woods, also abound more in waters than others, is a fact which may be asserted with little fear of contradiction.

CrlAr. V.--Of the Influence of 147oodson the r411nd and on the State of the .~tmosphere with respect to Health. Though many remarks which occur in this chapter are just, we are much surprised at some of the assertions, and we think we do not err in considering them unfounded. Among these is the assertion, that the impetuosity of the winds, where there are no woods to mitigate its violence, has rendered a great part of Great Britain barren. I f the author s eshmate, that the waste lands amount to ~ of the who e surface of Great Britain be true, it does not follow tttat these lands are barren in consequence of a deficiency of trees. The heaths in the north of Germany, which are not all situated in places entirely destitute of woods, show clearly enough that circumstances, which accompany an effhct, are not always those which produce it. The comparison_ between that .oart ~>f Tartary inhabited by the Calmucks and Lombardy, appears to he equally unfounded. Whoever, in this instance, though'the geographical latitude should be the same, expects to find the climate in both rezions alike, and ascribes the dissimilarity of the climate to the want ~'f trees in 3"artary~ must certainly have allowed many circumstances, which ought to have been taken into account, to pass unnoticed. .

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CaAr. VI.~influence of ~bods on the Fertility of the Soil W e also meet with many remarkable observations and importarA conclusions in this chapter. But upon the whole, we think that this

Wmw~.'s New Method oar t~ilterlng l~Uater, .

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essay must be considered as a work whieti: has not been~:r~iieete~ upon with sufficient deliberation. Neverthelessi it contains an abt~:/i~~ dent collection of curious facts; and though:some of these faet~are not well applied, and the accuracy of others remains to be:pro~ed, the book wilt, in the mean time, l~e found an excellent contribttfi0n~ towards the explanation of the subjects of which it treats. There are, occasionally~ some obscurities in the reasoning; but whether these ought to be attributed to the author or the trans!ator~ we have not at present the means of determining.

~ Quarterly Journal. Account of a new method of Filtering ~Vater, invented by Jx~tzs WHIT]':, Esq. Engineer. ThE filtration of water in a mountainous country like Scotland~ where water is in general pure, is comparatively a subject of less interest than in flat and fenny districts, or in great cities like London, which is supplied chiefly from the collected waters of the Thames. The means of purifying water under such circumstances, is a matter of tile first importance to the health and comfort of the community. It is well known, that, till of late years~ the want of good water has been severely felt in the lower parts of Lincoln, Kent] and other fenny districts. In some of these, where tl~e inhabitants and their cattle suffered much from the want of good water, the evil has lately been removed where this essential necessary of life has been supplied by means of perforations made to a great depth in the soil, by boring with an iron auger, so as to reach and bring to the surface the deepseated springs. In the metropolis, every one knows the great outcry which has of late been made about the polluted state of the Thames water for domestic purposes, arisin~ from this rivet" being the receptacle of the drainage waters of that¢overgrown city. In point of fact, las:n6ticed by our distinguished countryman, Mr. Stevenson, engineer,) t h e waters of the Thames are changed or renewed very slowly, n~ar4y the same body of water moving upwards and downwards as th~ti0e flows or ebbs. The inhabitants of London, therefore, m£]:hetually be said to be receiving into the stomach what had formerly passed through the public drains. This has become a subject o f so much notoriety and interest, that government has of late made it a matter of public inquiry, and has procured the report of a committee of professional men, consisting of a physician, a chemist, and a civil engineer. Ttle effect of these movements has been to produce numerous plans for supplying the city from a purer source, and also for filtering the water which it already possesses. Among these may be mentioned a plan by Mr. James White, engineer, of Oxford street, London, andanother by Messrs. Stirling and Son, of Lambeth, who have invented a machine called the "Rapid Filter," and obtained a patent for it. Having no drawing of Messrs. Stirling's apparatus,