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case, the task will be found to be impracticable ; but even when other microscopic alga. Not being myself within reach of a the overlap of the small disc is greater, the task can only be good library, I can only furnish your readers with a key to further achieved by actually making new cusps out of the irradiation information.
C. A. JOHNS fringes. (A figure would make this explanation much simpler.) Prof. Newcomb says that he is decidedly of opinion that the
IN NATURE of 28th September, Prof. Frankland, in introirradiation of an extremely minute thread of light is not the same with that of a large disc. He does not seem to notice that if ducing the ice flea to the readers of NATURE, uses the expression this is so, Venus just before, at, and just after internal contact,
“if known at all," and concludes by asking information about must be distorted.
it. The glacier flea, Desoria glacialis, waz noticed and described This even if--admitting the enlargement | by Prof. Agassiz as far back as 1845, in his Ascent of the Wetterof the sun's disc-he denies that the disc of Venus is reduced by horn on the 29th of July of that year. Not having Agassiz's irradiation.
work at present beside me, I cannot refer to it, but these fleas He fails also to observe that a peculiarity such as distortion, or
are noticed in an extract translated from an account of the ascent, the formation of a ligament, may escape the notice of inferior or
and published in Hogg's Weekly Instructor for Dec. 1845, vol. ii. not very attentive observers, and so all his negative observations
On the Aar Glacier they are described as being scattered be explained. It is no proof of superior skill in observation to
over the “surface of the snow in millions," elsewhere, see no signs of an illusory effect. Until we have observers who recognise no traces of irradiation when looking at the solar disc, being collected in masses under the stones on the ice.”
R. C. we must believe that (as Mr. Stone has, I think, already asserted)
The New Dynameter the non-recognition of distortion or ligament formation is due to inattention, or want of observing skill. That this should be more The letter from the Rev. T. W. Webb in your last number common than close and careful scrutiny is not a very surprising is a very tantalising letter. He tells us, and we could not wish circumstance, and proves nothing. RICHARD A, PROCTOR to have a better authority, that a new dynameter has been in
vented by the Rev. E. Berthon, but he does not tell us how it is
constructed or where it can be obtained. Oceanic Circulation
I may take this opportunity of mentioning a makeshift dyna. IN NATURE of August 17, I have just seen the report of the meter which I have found to answer very well when extreme discussion on Dr. Carpenter's paper on the above subject read at accuracy is not required. the late meeting of the British Association.
I have a pocket telescope fitted with Cavallo micrometer, Dr. Carpenter, explaining the movements on thermodynamic i.e., a slip of finely divided mother-of-pearl screwed to the dia. principles, states that he has " found the primum mobile of this phragm next the eye-glass. Unscrewing the two last draws of circulation was not in equatorial heat but polar cold,” and this telescope the end of the second is applied to the eye-piece explains that “
(1) As each surface-film cools and sinks, its place of the telescope of which the power is to be measured, and the will be supplied, not from below, but by a surface influx of the first draw pushed in till the image of the object-glass comes sharp water around ; and (2) the bottom stratum will flow away over upon the mother-of-pearl
. The diameter of the image is thus the deepest parts of the basin, while, since the total heat of the given in divisions on the mother-of-pearl, the value of which, in liquid is kept up, there will be an upper stratum which will be hundredths of an inch, has been previously ascertained. drawn towards the cold area, to be precipitated to the bottom
W. R. and repeat the action. Apply this principle to the great oceanic
Notaris on Mosses area that stretches between the equator and the poles, we should expect to find the upper stratum moving from the equator I am informed by Dr. Dickie that the genus Habrodon was dis
With reference to the notice of De Notaris' book on Mosses, towards the poles, and its lower stratum from the poles towards the Equator. That such a movement really takes place is indi
covered in Great Britain several years ago by the late Mr. McKin. cated, as it seems to me, by various facts."
lay, of Glasgow, and that he had received from Mr. Wilson It does not appear, however, that Dr. Carpenter has well estab
about two years ago from his district Conomitrium julianum. lished his claim to the theories in question, while, in a pamphlet Killin by Dr. Siirton.
Dr. Dickie sends specimens of Habrodon Notarisii gathered at on the same subject, published in 1869 by Dr. Adolph Mühry of
M. J. BERKELEY Göttingen, we find such passages as the following :-“ As the " In the review referred to, Prof. De Notaris was errocause of the latitudinal circulation we have assumed the difference neously described as of Geneva, instead of Genoa. --EnN. of temperature in the water between the equator and the pole.' He honestly gives Arago the credit of being, perhaps, the first to put forward this view in 1836; and after remarking (p. 11)
“ Newspaper Science” that it might le considered doubtful whether it is the upper warm My attention has just been called to a letter from Mr. David current from the equator or the under cold one from the pole Forbes which appears in NATURE, Sept. 21, under the head that ought to be considered the primary, he says (p. 12) “For “Newspaper Science,” and in which that gentleman, writing from us the primary “arm’ is the heavier, i.e., the colder polar stream, Boulogne, pathetically describes the emotions with which he read which, in obedience to gravitation, falls in a horizontal direction a recent "article" in the Globe on “Krupp's” Gun-manufactory toward the lighter water of the hot zone; and the secondary at Essen. I need hardly say how deeply I deplore the shock “arm’ is the returning antipolar. It moves to replace what which I have unwittingly been the agent of inflicting on your flows away, and is, therefore, the compensation-arm.
distinguished correspondent. It will be some small satisfaction Here, without following Dr. Mühry any further, we find the if you will allow me to express the hope that the “desired thermodynamic theory advanced by Dr. Carpenter, and his result” of Mr. Forbes's “reluctant " compliance with the advice primum mobile as well; but by giving him credit for ignorance of of his “medical man,” and most wise resolve “to eschew every Dr. Mühry's work, we may excuse him for laying claim to what thing scientific for the next few weeks at least, in order to recruit is there put forward, and accepting therefore the commendation before the winter labours commenced,” may not be utterly de. of others as unknowing as himself.
feated by the perusal of “a specimen of English scientific opinion," of which I am unhappily the author. It would be a
terrible reflection indeed, that a stupid error on my part had, Ice Fleas
perhaps, imperilled the accuracy and success of Mr. 'Forbes's During a recent ramble upon the Morteratsch Glacier, I also is winter labours.” The blunder (or rather blunders) occurred observed a large number of the minute black creatures described as follows :--), too, was “knocked up with work," but being by Prof. Frankland in NATURE, No. 100. My attention had myself a "medical man ”naturally only in part carried out my been directed to them ten years ago by Lord Anson on the own prescription. I would, for the sake of Mr. Forbes, and
snow-bone;;” near the summit of the Ægischorn. They are the credit of "English scientific opinion” in the estimation of only nominal “cousins” of the flea (Pulex) of civilised life, and his “French acquaintance,” I had exercised a little more disare not at all related to Dapnia, the "water flea,” but are closely cretion. However, unfortunately, I stumbled on the Krupp allied to the minute insects which are often seen on the surface of | factory, and all forgetful of my dilapidated mental condition, stagnant water, resembling grains of gunpowder, and skipping wrote a note-paragraph (I never write "articles "), which i partly by help of their forked tail, folded under them so as to vainly imagined might have been innocent and interesting. It is serve as a foot, hence their name Podura, or “skip-tail.". They not always possible to compress even the manuscript necessary have been named by Agassiz Desoria saltans. Their food, Ifor a paragraph on to a single sheet of paper, and I grieve to conjectured with Prof. Frankland, consists of “red snow" and say that after my paper had passed the editorial eye three words
forming the connecting link of a sentence must have been was found frozen to the under one. They were then dropped. What I intended to say, without the slightest notion separated, and one of them was allowed to remain supof giving a "technical or scientific" opinion, was, “The iron is ported at the ends and weighted by ice at the middle. În alloyed in crucibles, formed with certain clays and a preparation
a few hours it had bent into a curve, the versed sine of plumbago. The words italicised disappeared in some mys. of which from a chord uniting the two ends was, at least, terious way. The next of my idiotic sentences goes on to talk
two inches. In fact, when the rectangles are thin, and about the crucibles, or “creusets, as, to the great scandal of Mr. Forbes, I ventured to call them. If I could stop here, an
the weight carefully laid on, flexure commences very soon, humble apology for my fault might, perhaps, serve my purpose,
and may by cautious manipulation be rendered very conbut, alas! I have more to answer for. Vaguely dreaming of the siderable. I think Mr. Froude told me that in his foot-pound, I actually wrote kilometre for kilogrammetre, when experiment the molecules were “in torture," and that speaking of the power of the new steam hammer ; and, worst of they in great part recovered their positions when the all, I also wrOTE “Sheffield Gun Metal.”
weight was removed. In the foregoing experiments the Can I ever hope to be forgiven when thus I write myself flexure was permanent. down an ass?
MEDICUS I tried to bend the rectangle just referred to back again P.S. -As to the question whether Krupp invented the process by reversing its position and weighting it with the same employed at his factory, I offer no opinion “scientific' block of ice. But whether owing to my want of delicacy ordinary. I only repeat the impression which prevails.
in putting on the weight, or through the intrinsic brittleness of the substance itself, it snapped sharply asunder.
I left in your hands when quitting London an exceedFURTHER NOTES ON CERATODUS ingly interesting paper by Prof. Bianconi, in which are INCE the article on Ceratodus (published in NATURE, of, I think, lake ice. The foregoing experiments on
figured the results of various experiments on the bending Nos. 99 and 100), was written I have examined a
glacier ice confirm his results. mature female, transmitted, with other examples, by the
JOHN TYNDALL Trustees of the Sydney Museum to the National Collection,
I may add that various experiments were subsequently and am enabled to make the following additions :
made, and a means discovered of rendering the bending 1. The oviduct in its developed conditions is, with regard to its internal structure, surprisingly similar to that subject.-J. T., September 28
very speedily visible. I hope before long to return to the of Menopoma.
2. The ova are expelled through the oviduct, and not through the peritoneal slits; they receive in the oviduct a
THE MIGRATION OF QUAIL coating of an albuminous substance as in Batrachians. 3. The caudal termination of the vertebral column is
HE fact of this little bird having visited England
THE subject to individual variation. In one example the neural
this year in such numbers appears to have attracted
the attention of naturalists as well as sportsmen. In the and hæmal elements are continued far beyond the notochord, and are confluent into a tapering band, which is
columns of the Field may be found a census giving parti
culars of this migration. And it will appear a curious segmented, as is the case in some specimens of Dipterus or Ctenodus.
coincidence when I mention that there has been here a greater migration of quail this year than ever remembered before. Where they come from is somewhat mysterious.
They have been shot in hundreds in some paddocks, and ON THE BENDING OF GLACIER ICE * found as numerous as ever in ten days. I can only R. MATTHEWS and Mr. Froude had supported long
account for it by stating that it has been a most remark. MR. rectangles of ordinary ice at the two ends, weighted
able year for grass, and consequently cover was good ; and
this does not appear conclusive, for the grass has been them in the centre, and thus caused them to bend. The
good all over the country for hundreds of miles towards ice employed, if I recollect right, was of a temperature
the north, from which direction some appear to think they some degrees below the freezing point, and in my little Alpine
come. They are found generally in paddocks, where book recently published I expressed a hope that similar
thistles grow. Can there be any common cause affecting experiments might be made with glacier ice. I have been
these facts ? trying my hand at such experiments. The ice first em
Melbourne, August 10
AUSTRAL-ALPINE ployed was from the end of The Morteratsch Glacier, and when cut appeared clear and continuous. A little exposure, however, showed it to be disintegrated, being com
JARDIN D'ESSAI, ALGER posed of those curious jointed polyhedra into which glacier ice generally resolves itself when yielding to IN 1832 the then French Government conceived the warmth. Still, when properly supported and weighted,
idea of forming near the town of Algiers a botanical a long stout rectangle of such ice showed, after twelve garden, in which all plants likely to be easily grown in hours, signs of bending.
Algeria, and which might be useful either for their ornaI afterwards resorted to the ice of the sand cones, which, mentation, or from their economic value, should be kept as you know, is unusually firm. From it rectangles were
for distribution or for sale. A portion of ground situated taken from three to four feet long, about six inches wide, between the sea and the public road, and occupying the and four inches deep. Supported and weighted for a place of an old hamma or marsh, was selected for this considerable time, no satisfactory evidence of bending
purpose, which is about two miles from the town. In 1867 appeared ;, the bars broke before any decided bending the Emperor of the French conceded this establishment took place. Smaller bars were then employed. Two to the “Société Générale Algérienne," under whose of these were placed across the mouth of an open auspices, but under the direct superintendence of M. square box, their ends being supported by the sides of the Auguste Rivière, the gardens at present are. box. They formed a cross, and a clear interval of at least
In addition to the level swamp, the gardens now also an eighth of an inch existed between them where they occupy the slope of a low hill on the opposite side of the crossed. The upper one was carefully weighted with a road. The level ground is laid out in alleys which open block of ice; after two hours it had sunk down, and out into a circular boulevard which surrounds the whole
garden. Carriages are admitted to the circular drive only, * The following is an extract from a note addressed to Prof. Hirst, and foot passengers to the cross walks. A stream of fresh sent from Pontresina in the hope that it would reach Edinburgh in sufficient water runs through the grounds, forming in one place a time to be communicated to Section A of the British Association. It was a few hours too late.-J. T.
One fresh from the Botanical Gardens of Europe is the great level portion of the garden. Outside of this, and astonished at every step taken in the Gardens by the on the other side of the roadway, there is a small hill
, two wondrous vegetation which is shown by all the semi- or three hundred feet in height, which slopes towards the tropical plants. Descending a few steps from the circular garden and the sea, and is traversed by several ascending drive, a great palm avenue is entered. This avenue was walks. This is the New Holland district of the garden, planted in 1847, and is formed of about eighty trees of and certainly not the least interesting portion of it. In ihe date palm, nearly as many of the Latania Borbonica, one section of it are different species of Acacia, many of and about 150 of the dragon's blood tree (Dracena draco). them large trees, twenty to twenty-five feet in height. Of The avenue is about ten yards wide, and between every the Proteaceæ there were magnificent trees; of the genera two of the date palms there are two of the dragon's blood Banksia, Hakea, and Grevillea, the collection of species tree and one Latania. It terminates in a clump of palm was very large, all of them just bursting intomasses of bloom. trees which are planted almost to the border of the sea, The most important of the trees growing in this corner of When it is borne in mind that the date palms are from the hill was probably Eucalyptus globulus, of which some twenty to fifty feet high, the Latanias averaging about trees, now about forty feet in height and over four feet twelve, and the Dracænas about eight seet in height, and a half in circumference, were planted in 1862, and the general effect of this splendid avenue may be were then only a few inches high. Young well-established imagined. All the trees were in December last in seedlings, of about ten inches in height, are sold for 20s. full flower or fruit, the golden trusses of the date a hundred, and large numbers of them have been planted palm contrasting well with the more brightly-coloured from time to time throughout Algeria by the French Goclusters of Latania berries. It would require more space vernment. This species grows in Algeria with most surthan is at our disposal to describe the contents of all the prising rapidity, under very favourable circumstances various small avenues that branch off from the main one. growing eighteen to nineteen inches in height each The most remarkable smaller avenues are, perhaps, the one month. Its wood appears to be hard, close in the grain, formed of bamboo (Bambusa arundinacea), planted in 1863, and it is largely used in the construction of quays, and forming an immense mass of foliage, the stems support- bridges, and railways. This tree seems to do so well ing which are from forty to fifty feet high, and that sormed of on the southern side of the Mediterranean that we think about 100 plants of Chamærops excelsa, each about ten feet | its culture ought to be successfully attempted in the south in height. But remarkable as are these charming sub- of Spain, in Sardinia, in Sicily, and the southern parts of tropical alleys, the visitor is more than surprised when on Italy. In districts subject to heavy winds it requires for going towards the portion of the garden where the plants some years-owing to its rapid growth-some protection, are grouped somewhat according to their natural orders, but in places sufficiently warm for it, it ought to repay well he finds specimens fifteen seet high of Caryota urens and for any little extra care it might be found to need.
with did not fruit ; of. Oreodoxa regia, from Cuba; several plants succeed in these gardens, we may mention the Cedrus upwards of twenty-five feet in height; and a plant of deodara; but Casuarina equisetifolia was flourishing, and Jubaa spectabilis, which is twelve feet high ; and then one tree of Araucaria excelsa was about sixty feet in just a few steps more and a parterre alloted to the height, and measuring a little over nine feet in circumnatural family of the Musaceæ comes to view. As ference at its base. both the plantain and banana are grown in large The object of the Society in keeping up these Gardens quantities for their fruit in another portion of the grounds, is, as we said, to introduce into Algeria all useful and the family is here chiefly represented by such genera as ornamental plants likely to grow there. In addition they Strelitzia and Ravenalia. Magnificent specimens of the grow enormous quantities of young palms and other latter genus, with stems nine to ten feet high, exhibited ornamental plants for exportation to Europe, and some great combs of flowers. We are not aware is the Travel- few plants interesting to the botanist for exchange with ler's tree has flowered in Europe, and we were not pre other establishments. In a place so savoured by nature pared to find it in full flower in Algiers. It has not, and so easily accessible to Europe, it would be, we however, matured its fruit in this garden. Near this venture to think, well worth the while of the director of grand parterre stood another with many fine specimens these Gardens to considerably enlarge the last portion of of Yucca, also a magnificent plot of Aralias, A. papyrifera, the Society's design. How many tropical plants are yet in full fruit and very handsome ; the fine A. leptophylla unknown to the large collectors of Europe, and what a and A. præmorsa, thickly covered with spines, and the vast percentage of deaths occur among the collections very ornamental A. furinifera; and then one's attention is sent from the tropics at any season of the year to our caught by a large tree (Carolinea macrocarpa) from Brazil, shores! But with Gardens like these at Algeria, situated with a couple of dozen of its fruit, each as big as a on the sunny side of the Mediterranean, to act as a halfcocoa nut; by a small forest of Anona cherimolia way house, the resources of the Botanical Gardens or in full fruit, which is nearly as good as that of the establishments of the North would be indefinitely inclosely related species which yields the custard apple. creased. Another purpose for which these Gardens might Near these is an immense tree some thirty feet in be made most useful is for forming a collection of speciheight, covered with fruit of the Avocado pear (Persea mens of plants or fruits of economic interest. Many of gratissima); and at its feet is a quantity of guava trees the fruits, stems, &c., which ripen in these Gardens as (Pisidium Cattleyanum) crowded with its perfectly ripe, easily as cherries or potatoes with us, are not to be seen large, pear-shaped, golden fruit. Growing up into the in some botanical collections, and are not, in Europe at trees, and forming numerous and never-ending festoons, least, to be purchased. How gladly would some botanist were some specimens of Cacti, chiefly species of Cereus. buy such as we here refer to if they were on sale, say Some of these were of great size, and one specinien, at the depôt of the Algerian Society in Paris ; and the which had completely strangled a plantain tree some expense of putting up such in salt and water would be twenty-five feet, was said to have been covered in the a mere nothing. The same remarks would apply in many autumn with 600 to 700 flowers. It must have been a cases to portions of the roots of remarkable genera, and sight worth a long pilgrimage to see.
also to flowers. In calling attention to these Gardens, we Enough has been said to show what a surprising venture to suggest these hints to their well-known director, number of semi-tropical fruits luxuriate in the beds of and also to that indefatigable botanist who, more than this well-watered garden, and we might add many any other, now represents science in connection with the well-known vegetables to the list, as sweet batat, yam, Algerian Society, Prof. Durando of Algiers. papaw; but all this while we have been writing of
E, P. W.
THE TEMPERATURE OF THE SUN atmosphere, the relative density of which, at correTHE increase of the volume of atmospheric air, under sponding beights, is obviously as correctly repre- . constant pressure, being directly proportional to the
sented by this diagram as that of the solar atmo. increment of temperature, while the coefficient of expan-sphere. It is true that, owing to the greater height sion is o'o0203 for 1° of Fahrenheit, it will be seen that a
of the latter compared with the attractive force of temperature of 3,272,000° Fah. communicated to the
the sun's mass, the upper strata of the terrestrial almo. I
sphere will be relatively more powerfully attracted than terrestrial atmosphere would reduce its density to the upper strata of the vastly deeper solar atmosphere.
6643 The ordinates of the curve a d b will therefore not repreof the existing density. Accordingly, if we assume that the height of our atmosphere is only 42 miles, the eleva-crepancy, however, resulting from the relatively inferior
sent the density quite correctly in both cases. The distion of temperature mentioned would cause an expansion increasing its height to 6643 X 42 = 279,006 miles. This sphere, will be very nearly neutralised by the increased
attraction of the sun's mass at the boundary of its atmo. calculation, it should be observed, takes no cognizance of density towards that boundary, consequent on the great the diminution of the earth's attraction at great altitudes, which, if taken into account, would considerably increase
reduction of temperature--sully 1,380,000° Fah.- caused
by the dispersion of the solar rays before entering space. the estimated height. Let us now suppose the atmosphere it may be well to add that, in representing the relative of the sun to be replaced by a medium similar to the terrestrial atmosphere raised to the temperature of beight and pressure of the terrestrial atmosphere, a c in
our diagram indicates forty-two miles, while b c indicates 3,272,000°, and containing the same quantity of matter as the terrestrial atmosphere for corresponding area. Evi
a pressure of 14'7 pounds per square inch ; and that in
representing the solar atmosphere, a c indicates 100,000 dently the attraction of the sun's mass would under these
miles and b c 410 pounds per square inch. Bearing in conditions augment the density and weight of the supposed
mind the high temperature and small specific gravity, the atmosphere nearly in the ratio of 279 : 1; hence its
extreme tenuity in the higher regions of the solar atmoheight would be reduced to 279,006
10,000 miles. But sphere will be comprehended by mere inspection of our 279
diagram. Already midway towards the assumed boundary, if the atmosphere thus increased in density by the sun's the density of the solar atmosphere is so far reduced that superior attraction consisted of a compound gas princi- it contains only 13 boy of the quantity of matter contained pally hydrogen, say 1-4 times heavier than pure hydrogen, in an equal volume of atmosphere at the surface of the the height would be 10 X 10,000 100,000 miles. The
earth. pressure exerted by this supposed atmosphere at the Let us now consider the diminution of intensity occasurface of the photosphere would obviously be 147 X 279 sioned by the increased depth through which the heat rays
410 pounds per square inch, nearly. Unless, therefore, pass which are projected from the receding surface of the the depth greatly exceeds 100,000 miles, and unless it can photosphere. Fig. 6 represents the sun and its atmosphere be shown that the mean temperature is less than extending of the semi-diameter of the photosphere, mh, 3,272,000° Fah., the important conclusion must be ac- cg, &c., &c., being the heat rays projected towards the cepted that the solar atmosphere contains so small a earth. The depth of the solar atmosphere at a distance quantity of matter that notwithstanding the great depth of 8 of the radius from the centre of the luminary, it will offer only an insignificant resistance to the pas- will be seen to be only 2'0012 greater than the versage of the solar rays. Now, the assumed mean tempe
Now, careful actinometer observations rature, 3,272,000, so far from being too high, will be found enables us to demonstrate that when the zenith distance to be considerably underrated. It will be recollected that is under 60°, the radiant energy of the sun's rays in passthe temperature at the surface of the photosphere, deter- ing through the terrestrial atmosphere is very nearly in mined by the ascertained intensity of solar radiation at the inverse ratio of the cube root of the depth penetrated the boundary of the earth's atmosphere, somewhat exceeds (see the previously published table). The increase of 4,035,000°. Consequently, as the diminution of intensity depth resulting from atmospheric refraction, it may be caused by the dispersion of the rays, will be inversely well to observe, is too small at moderate zenith distances as the convex areas of the photosphere and the sphere to call for correction; nor does the atmospheric density formed by the boundary of the solar envelope, viz., vary sufficiently during bright sunshine to affect the radiant 1'52 : 1, the temperature at the said boundary will be
intensity appreciably. The table adverted to shows that 4.035,000 = 2,654,600
an increase of the sun's zenith distance of 5' in 60° occasions 152
a diminution of temperature hardly amounting to 0'044° The true mean, therefore, will be 3,344,800', instead of Fah. Adopting the same rate of retardation for the solar 3,272,000° Fah, a difference which leads irresistibly to atmosphere as that observed in the terrestrial atmosphere, the inference that, either the solar atmosphere is more than it will be found that the loss of radiant energy of the 100,000 miles in depth, or it contains less matter than the solar rays at of the radius from the border of the terrestrial atmosphere, for corresponding area. It will be photosphere will be only 1'26 greater than at its centre. demonstrated hereafter that the retardation of the rays pro- According to the researches of Secchi and others, the loss jected from the border of the photosphere consequent on is fully three times greater than that established by the the increased depth of the solar atmosphere (supposed to be rate of diminution which we have adopted. This circumthe main cause of the observed diminution of energy near stance, in connection with the extreme tenuity of the solar the sun's limb), cannot appreciably diminish the intensity atmosphere, rendering any considerable loss improbable, of the radiant heat. The ratio of diminution of the points to the fact that some other agency than increased density of the gases composing the solar atmosphere at depth is the true cause of the diminution of the temperasucceeding altitudes, is represented by Fig. 5, in which the ture under consideration. Accordingly, the writer some length of the ordinates of the curve a d v shows the degree time ago instituted a series of experiments with incanof tenuity at definite points above the photosphere. This descent cast-iron spheres, for the purpose of ascertaining curve has been constructed agreeably to the theory that the practically if the reduction of temperature could be densities at different altitudes, or what amounts to the same, accounted for solely on the ground that the obliquity of the weight of the masses incumbent at succeeding points, the rays diminishes their energy. Previous experiments decreases in geometrical progression as the height above had demonstrated that the accepted doctrine is quite inthe base increases in arithmetrical progression. The correct, which teaches that heat rays emanating from the vertical line a c has been divided into 42 equal parts, surface of incandescent radiators are projected with equal in order to facilitate comparisons with the terrestrial energy in all directions. It was found during those
experiments that the ratio of diminution of radiant heat transmitted to a stationary thermometer by an incandescent circular disc of cast-iron, turning on appropriate journals, is directly proportional to the sines of the angles formed by the face of ihe disc and lines drawn to the centre of the bulb of the stationary thermometer. It was clearly shown that those heat rays only which are projected at right angles to the face of the incandescent radiator, transmit maximum energy. The important bearing of this fact with reference to temperature transmitted by the heat rays of the photosphere from points near the border, is self-evident. The small angle formed by the ray Cs, Fig. 6, and the tangent cf of the surface of the photosphere at c, explains satisfactorily why the radiant heat at a distance of ad of the radius from the sun's border, is considerably less than at the centre. It will be perceived that the angle fed diminishes very rapidly as the border of the photosphere is approached, and that when the extreme point is reached, the radiant
heat transmitted would be infinitesimal if the irregularity of the surface of the photosphere did not present a series of inclined planes capable of projecting heat rays in a direct line with kl.
Laplace, in the famous demonstration by which he proves that “if the sun were stripped of its atmosphere, it would appear twelve times as luminous ” (Mecanique céleste, tom iv., pp. 284–288), commits the grave mis. take of assuming that all rays emanating from a radiant sursace possess equal energy. This assumption leads him further to the erroneous conclusion that the rays projected from the retreating surface of the sun near the limb, act as rays from a lens, being crowded together in consequence of the obliquity of the radiant surface, thereby, he supposes, acquiring increased intensityhence the monstrous assertion of the great mathematician that, but for the interference of the solar atmosphere, the luminosity would be eleven times more intense.
The important question whether the solar atmosphere possesses any appreciable radiant power, and whether the