adjusted to that of the dividing-plate. , nected with his beautiful discoveries, Many skilful mechanicians do not be- are still in operation; and I shall, therelieve this to be possible; it is, however, fore, abstain

from mentioning some reasserted, that M. Gambey accomplishes sults which I have obtained on the abit with invariable success, by connect-sorption or interception of the chemiing the tracing-point with an articulated cal rays. The same reserve, it is clear, train of great simplicity. The great cannot be asked of Mad. Somerville. I, excellence of M. Gambey's instruments therefore, see no reason to refuse to the results, principally, from the ingenious interesting experiments of a person so tools he has designed for their fabri. eminently distinguished, all the pubcation. The theodolite of Mr. Pentland licity which the meetings and reports repeats both horizontally and vertically, of the academy can confer." and such is the truth and clearness of M. Arago then communicated the the graduation, that, though the circles following extract of a letter, addressed are but 6'3 in. radius, they can be read to him by Mrs. Somerville, detailing, off with the greatest certainty to five some experiments on the transmission seconds.

of the chemical rays of the solar spec

trum through various media. Chemical Rays of the Spectrum.Mrs.

“ I used in these experiments some Somerville, M. Arago, and Sig.

chlorate of silver, of the most perfect Melloni.

purity and whiteness, which Mr. Faraday had the kindness to prepare for me.

It In the report of the meeting of the was fluid, and could be laid very evenly Académie des Sciences, on the 21st of on paper. Although this substance is December, 1835, it was stated, That extremely sensible to the action of the after having pointed out the remarkable chemical rays, yet as there are no preparts of the experiment, by means of cise means for measuring the changes which Sig. Melloni proved, that the solar of colour produced by this action, there rays may preserve all their luminous is a difficulty in accurately describing properties, and yet, at the same time, results, when it is desired to compare lose all their heating powers, M. Arago tints which are nearly the same; but remarked, that the question might be the results which I now offer, are chosen regarded from another point of view. from such as do not admit of any In his opinion, it would be important to doubt. examine, if the processes employed by A small piece of glass, of a very Sig. Melloni, or some analogous ones, pale green, perfectly transparent, and would not lead to the fact of depriving less than 20 in. in thickness, did not the solar rays of their chemical effects; permit the passage of any chemical ray if, in a word, of the three properties whatever; after an exposition for half which solar light possesses when it an hour to the sun when very hot, the reaches the earth, viz. 1, that of illumi- chlorate of silver, which was placed benating ; 2, that of heating ; and 3, that hind the glass, exhibited no change of of decomposing, or affecting chemical colour. combinations, it would be possible to "I repeated this experiment with remove the two last, and preserve the several different green-coloured glasses, illuminating property only.

of various tints and thicknesses. I found “This experiment," "continued M. them all nearly impermeable by the Arago, appears to me as if it would chemical rays, even when they were produce some curious consequences, and submitted a much longer time to the in the past week I had nearly yielded solar influence. As Sig. Melloni has to the temptation of trying it. But, as already discovered that glass of this it was possible that Sig. Melloni might colour intercepted the most refrangible also have thought of it, though he has not of the calorific rays, we shall be induced, mentioned it in his memoir, it appeared by considering his results with mine, to me that I ought not to pursue my to conclude, that this glass has the prointention, until after I had conferred perty of intercepting entirely the most with the learned Italian physicien." refrangible part of the solar spectrum.

“ The motives, which influenced me Plates of deep-green mica are also in 1835," observed M. Arago to-day, nearly impermeable by the chemica) (17 Oct. last,) “not to anticipate Sig. rays, but when the plates are very thin, Melloni in an inquiry so intimately con- and the solar action is very much pro


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longed, it is evident they do not in- it varies in some, even where the colour tercept the rays entirely. I fixed, by is nearly the same; thus, deep-red glass means of soft wax, on a sheet of paper scarcely permits the passage of any prepared with chlorate of silver, a plate chemical rays, while the garnet, equally of pale-green mica from Vesuvius, the deep-red, transmits nearly the whole of thickness of which did not exceed fin. them. The white topaz, as well as the I exposed the whole to the rays of a hot blue, the pale-blue beryl, cyanite, heasun; at the end of some time, the mica vy spar, the amethyst, and various other was removed, and I found that the por- substances, transmit with great facility tion of paper which it had covered had the chemical eays; but the yellow beryl lost nothing of its whiteness, while all may be said to permit none to pass ; the other part had acquired a deep- and the brown tourmalin, as well as the brown colour.

green one, has so little permeability, "A similar experiment was made that I failed in the different attempts with thin plates of white mica : six plates which I made to polarize the rays in of ordinary white mica being super- question, although I am of opinion, that posed, did not intercept the chemical the thing would not be absolutely imrays; the chlorate of silver which they possible with plates prepared much covered, becoming, at the end of an thinner than those which I employed. hour's exposition to the sun, of a deep- I intend to resume, shortly, this train brown. The same result was obtained, of experiments.” with a single, but much thicker, plate

Goethe and De Candolle. ofwhite mica. This substance, therefore, appears not to offer any obstacle to the "GOETHE, the greatest poet and the most passage of the calorific (chemical ?) rays. distinguished philosopher of Germany,

" These experiments disposed me, in was afflicted, about the middle of his the first instance to believe, that all career, with severe depression of spirits; green substances possessed the same the social and civil disorders 'of France property, but I was not long in finding induced such moral agony, that, during that I had been too hasty in general- his attack of hypochondria, he withizing results; in fact, having submitted drew to a retreat in Italy, to pass the to the same tests a large emerald, the time among the magnificent gardens green colour of which was very fine, but which embellish that country. Thesymnot very deep, and whose thickness was pathies of the poet were at first scarcely at least 3 in. I found that the che- excited by the contemplation of these mical rays were transmitted without exquisite scenes; but by degrees the difficulty ; therefore, the matter which flowers tlattered his senses, and as a colours the emerald green has no action means of recreation, his soul indulged on the chemical rays, while that which in their gorgeous beauties. At the same imparts the same colour to glass and time that their variety called forth his to mica, exerts a decided influence upon admiration, and he distinguished their them.

differences, he was struck with their Rock-salt, as there was every rea- analogies. He believed in their transson to expect, possesses, in a very high lation of form ; this intuitive poetry degree, the property of transmitting the consoled him, and became such an everchemical rays.

Glass, coloured violet springing source of pleasure, that the by manganese, and the deep-blue kind conception of a work on Vegetable Phywhich is used in finger-glasses for the siology was a consequence.

Goethe table, transmit these rays rapidly. The committed his inspirations to writing, change of chlorate of silver by the solar and gave them the form of aphorisms, action takes place quickly, though a intending them for his private use only. plate of deep-blue glass, įin. thick, be At a later period, in 1790, he sent his interposed.

work into the world, under the title of Among the various substances an Essay on the Metamorphosis of that I have exposed in these experi- Flowers. ments, rock-salt, white, blue, and violet “ Tlie human intellect was not then glass, are those which present the max- prepared, in the slightest degree, to reimum of permeability to the chemical ceive, under so anomalous a form, this rays; green glass and green mica pos- revelation of relations; and at the presess the minimum. Other bodies have sent day, how many botanists are there this property in intermediate degrees; who are arrived at this point ?



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Three years passed away, and Goethe, the south-east of Siberia; Hr. Sabler, resumed his wonted occupations as poet assistant-astronomer of the University and philosopher; but he felt so little of Dorpat; and Hr. Savicht, Professor confidence as a naturalist, that he fre- of Mathematical Sciences in the Uniquently made secret incursions into the versity of Moscow. These are accomregions of zoology and of anatomy, to panied by a mechanician, and furnished search for proofs and analogies to sup with a complete selection of the necesport and justify the law of harmony sary instruments. The time required which he had discovered in the vege- for the operations is estimated at about table tribes, for he had faith in his own eighteen months. The line of this verconvictions, and in the tardy justice of tical survey is to be conducted trigonoposterity.

metrically, and will be run, according to L"Twenty-seven years after Goethe had local circumstances, either between Tabeen left in the rear as a naturalist, or ganrog and the mouth of the Kouma, rather forgotten under the title, his along the Manitch, and across the day of triumph arrived. De Candolle steppe, or between Taman and Kisliar, appeared with the rich booty he had following the range of the Caucasus. collected during his admirable researches Simultaneous barometrical observainto the teratology of vegetables. De tions, with instruments regularly comCandolle, who had passed through every pared, will be made, not only by the grade of botanical knowledge, adopted, travellers along the line of operation, under a slightly-different form, the but also at Astracan and at Taganrog, notions of the great poet on the analogy by experienced and confidential persons of organization, and immediately after- stationed in those towns. wards determined to visit, at Weirnar, the illustrious old man who had enun

Mirage in Iceland. ciated these excellent ideal preconcep- “We have had very often the phenome tions in the science. There, cordially non of the mirage under observation; congratulating the philosopher, so tar- and, contrary to the opinion of some dily admitted to the title, he beheld in navigators who have visited the North, him a real naturalist, in the midst of a I was never able to remark that objects valuable cabinet of natural history, and were elevated by it. It always appeared occupied in observations upon living to me like a bright fog on the surface beings!"--GEOFFROY SAINT-HILAIRE. of the sea, which, variously modifying

the bases of objects, might, I believe, Grand Scientific Survey, by order of in certain circumstances, so influence the Russian Government. the illusion, as to give an idea of their

being elevated by the phenomenon."A SCIENTIFIC expedition for the purpose ROBERT. Letter from Iceland, July, of accurately determining the long-dis- 1836. puted question of the levels of the Cas- When this extract was read in the pian and Black Seas, was to commence Académie des Sciences, M. Libri reits operations in July last.

marked, that it could not be affirmed, The government of Russia has un- as M. Robert appeared to do, that dertaken it on the suggestion of the objects were not elevated by the mirage, Imperial Academy of Sciences, at St. for this phenomenon, which takes place Petersburgh. It has approved of the under very different circumstances, proplan of operations drawn up by the duces very varied effects. In the sandy Academy, and munificently placed countries of the south, lakes and sheets 80001. at their disposal to defray the of water are seen during the mirage, expenses.

while in the north and at sêa, it is very The details of the organization of this distant objects only, and even those expedition, and the selection of the sci- below the horizon, that are visible. As entific corps who are to carry its opera- | to whether these objects shall be seen tions into effect, have been confided to elevated, more or less, by the effect of Professor Struve, the astronomer of of the mirage, that will principally deDorpat. He has appointed three of his pend upon local circumstances, and the former pupils ; Hr. George Fuss, assist- state of the atmospheric strata through ant-astronomer of the Central Observa- which the rays must pass which ematory, and who has given evidence of his nate from the objects affected by the ability by his labours in China and in phenomenon.

Geological Hebrer. Extemporaneous malleable Platinum.

In sawing through a block of marble, “The process of Wollaston for the (primitive limestone,) which had been manufacture of platinum is made use of obtained from a quarry in Montgomery by those persons only who manufacture county, Pennsylvania, there was found in this metal for commerce.

Chemists the interior a cavity filled with black never prepare inalleable platinum for pulverulent matter, which was denomithe uses of the laboratory, and the pro

nated primitive carbon. When this cess is described in no public course of was removed, the bottom of the cavity, instruction. Hr. Liebig is, I believe, the which was flat, presented several lines only person who in his lectures teaches in relief, which portrayed, distinctly, it. Though the mode he follows is two letters of the Hebrew alphabet ! exactly, in every respect, that of Wol- | It appears that the attention of Amelaston, and though it presents nothing rican naturalists has been strongly new in a scientific point of view, i directed to this discovery. Mr. Browne, nevertheless am of opinion that I shall Professor of Geology at Philadelphia, perform a useful and agreeable office to and the present possessor of the block, chemists, in directing their attention to has offered to send it to Paris for the a process far too much neglected, and examination of geologists. so easy of execution, that one may say

Motion of Water on Heated Surfaces. there is really no operation whatever more simple, or more expeditious, than PHYSICIENS have long remarked the that of making malleable platinum in phenomenon which water presents when the following little apparatus.

thrown upon a metallic surface heated "It is a hollow cylinder, slightly to a very high temperature. If a small conical, one end of which is closed by a quantity of water be thrown into a crusmall thick metallic plate. After hav- cible of platinum at nearly a white ing decomposed, at the lowest possible heat, for instance, the drops will be seen temperature, the ammoniacal muriate of to be tossed about from one side to the platinum, the froth produced is to be other of the crucible, or to spin round removed by a wooden rod, and mixed on themselves, but always continuing a with water, after being made into a very long time, though their evaporaclear paste it is to be introduced into tion would have been rapid, had the the cylinder; then, by means of an iron metal been less hot. M. Baudrimont piston, it is to be slightly pressed for has concluded, from experiments made one or two minutes ; this is to be fol- with a view to explain the phenomenon, lowed by the greatest possible compres that the drops of water so moving at sion. A ring of iron in which the the bottom of an incandescent crucible, cylinder stands, permits the easy dis- have a temperature much below that of engagement of the bit of platinum, by ebullition, and that it never exceeds striking a blow on the piston.

122° Fahr. M. Laurent, in repeating “ The platinum, when thus removed, these experiments, obtained very differwill be found to have already acquired ent results ; according to him, the great density, and a brilliant metallic water, notwithstanding the slowness aspect. It should be dried gently, and with which it evaporates, has a tempeafterwards exposed for a quarter of an rature approaching very nearly to 212". hour to a white heat, then be sud- | M. Laurent also does not admit, that denly withdrawn from the crucible, and the drops, during the whole time of struck once with a hammer. It is their existence, are separated from the to be so treated four or five times, bottom of the crucible by a thin sheet of gradually augmenting the number of vapour; he believes that, on the conblows.

trary, they leap continually, and that at “In less than half an hour the whole each of these bounds they touch the operation is finished, and is so easy, incandescent surface, though for a very that the result is always certain. short time only. During these move

“I offer for the examination of the ments they present a singular appearAcademy a spatula and a kvife-blade ance; their outline, instead of being of platinum, which I saw manufactured, circular, has projections more or less in in a few minutes, in the laboratory of number, but always of an even number. Hr. Liebig, at Giessen."— PELOUSE. “ It is in the following way," says

M. Laurent, “ that the generation of whatever, and the superficial content of these forms may be understood. Let it is marked immediately upon a dialus suppose an elastic circle suddenly plate by an index. compressed in two points, diametrically M. Caïro, who has also devoted himopposed to each other; it will take the self to reduce the calculation of surform of an ellipse; but if the compress- faces of land, &c. to a purely graphic ing cause be suddenly annihilated, the operation, substitutes for the figure proellipse, by its elasticity, will return to posed a number of trapeziunis, having the previous circular form, and, by vir- their bases parallel, and their height tue of the velocity acquired, will not constant. This latter quantity is taken stop there, but proceed to form a second as the unit, so that if the mean bases ellipse, the greater axis of which will be are successively measured, the nuinperpendicular to that of the first. Thus ber of linear units contained in the There will succeed a series of oscillations sum of all these bases expresses that of which will give ellipses whose greater the superficial units contained in the


are alternatively perpendicular figure proposed. to each other, and, if the movement be For a very long period it has been cusvery rapid, the impression of a previous tomary to calculate approximatively the ellipse will remain on the retina, when area of an irregular curve, by means of that of a succeeding one is produced equidistant ordinates taken so near to upon it, and the two images will be each other that the portions of the superposed in such a manner, that they curve intercepted by them may be conwill exhibit a cross with rounded ends, sidered, without any sensible error, to or a wheel with four teeth. If the be short right lines. A much greater images of the two extreme ellipses, and degree of precision is, bowever, attained that of their mean circle, be seen at the by considering the given curve, on the same time, a star of eight points will be contrary, as an assemblage of small produced, &c. It is easy from this to parabolic lines, in which three points see why the number of projections of are known. Legendre, in his Exercices the figure should always be of an even de calcul intégral, has, in certain renumber.

spects, improved this method. It is also “That which has heen said of a circle given in several other modern works. will hold of a sphere, if it be elastic, as

But in the operations of the most extenis the water-drop on the floor of an sive surveying, even in the most imincandescent crucible.

portant of them, the former process “I convinced myself that these forms may be safely employed; and it is this were owing to vibratory motion, by the which M. Caïro uses. following experiment. I placed in a por- Although, in general, the area of any celain cup about an ounce of mercury; irregular figure bounded by a curved I set the cup on an elastic board, which line, may be easily obtained by means I made to vibrate with a violin-bow. of the tachymeter, yet when the space The mercury presented immediately to be measured is any right-lined polythe same figures as the water in the gon, it is desirable to select a mode of heated crucible.”

decomposition which will lead to the

end desired in the most simple and Instantaneous Calculation of Areas.

convenient manner. Now, in these

cases, the instrument of M. Caïro, even M. GAETANO Caïro has invented an following the process which he has instrument, to which he has given the himself described, abridges but very name of Tachymeter (rapid measurer). little the ordinary method of finding Its object is to give the area of plane the area of a triangle, rectangle, &c. surfaces bounded by any outline what the bases and heights being known. ever, without the necessity of any arith- Finally, though the tachymeter does metical operation.

not give, under any circumstances, the There are several means more or less area of a plane figure with the same rapid for ascertaining the areas of plane celerity as the instrument of MM. surfaces, among which that of the plani- Oppikofer and Ernst, it is, however, of meter of MM. Oppikofer and Ernst a very simple construction, and it may has the remarkable property, that no- be advantageously substituted for the thing more is necessary than to draw a graphical methods used in surveying.– point over the outline of any figure PUISSANT.

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