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the ambient air itself, that frigorific im- marked the same quantity when depressions were communicated. When pressed to an angle of 30 degrees above the sky was in its most serene state, fri- the horizon. But had this impresgorific impressions of 40 or 50 mille. sion of five degrees penetrated disimal degrees were indicated from rectly through the clouds from the every part of the hemisphere. Those higher regions of the atmosphere, proceeding from the zenith, and those the oblique passage presenting a diafrom the surrounding parts, were ex- meter so much greater, would have actly equal. It was thus ascertained scarcely allowed one half of a degree that the action of a given section, or to escape through the mass.

The angular portion of the sky, is the same fact proved that the clouds acted as at every obliquity. Dr Wells had

Dr Wells had a perfect screen, absorbing or extinfound, that the appearance of the guishing all the hot or cold pulses least cloud or thickness in the atmo. which it received from above, and sphere nearly destroyed the effect of then acted in its turn downward, comcold radiation, and produced an ap- municating pulses of its own as an inproach to equality of temperature in dependent radiating body. Clouds the thermometers placed in contact consist merely of dispersed aqueous with different sorts of surfaces. Mr globules, and their influence is illustraLeslie's delicate apparatus shewed ted by that of water in the fluid state. with greater precision that the effect Mr Leslie inclosed a pyroscope in an was not entirely destroyed, but con- inverted spheroidal cup, and suspendtinued in a greater or smaller degree ed it a few feet above the ground, according to certain definite circum- while the sky appeared clear and blue. stances. With the erect spheroid, he He then passed a silver tray under found in cloudy weather, that the fri- it, which received the impressions gorific impression diminished in pro- from the sky, and by reflection transportion as the humid mass floating in mitted them to the inverted instruthe atmosphere seemed to descend. ment. The coldthus reflected, amountWhen the sky was canopied with high ed to 25 degrees; but on pouring a Aeecy clouds, the effect on the in- sheet of water over the silver tray, the strument might amount to 20 de- effect was absolutely and immediately grees; but when the vapours sank extinguished. For conducting such so low as to hover on the hilly tracts, meteorological observations, Mr Lesthe impression did frequently not lie has constructed an instrument on exceed five. The effect, therefore, a fixed scale, not only in its thermoevidently depends on the altitude of metrical degrees, but also in the exthe lowest range of clouds, and seems tent of reflecting surface, as proporto result from the difference of tem. tioned to the surface of the sentient perature which prevails there, com- ball. This beautiful instrument will pared with that of the surface of the be found a valuable accession, not earth, or other situations in which the only to meteorology, but to physical apparatus is placed. The same con- science in general. He has termed clusion was drawn from another set it the Æthrioscope, from the Greek of observations. In a calm day, when term asbgcos, which, in reference to the a mass of dark clouds was spread at atmosphere, signifies at once “ clear, no great elevation above the surface dry, and cold." The sensibility of this of the ground, the spheroidal appara- instrument is very striking ; the litus indicated only tive millesimal de. quor instantly falls and rises in the grees in a vertical position, and still stem with every passing cloud. Somo of its variations are not quite ac- heated room and directed to the ceilcounted for; as of two days of equal ing, or placed near the ceiling and apparent clearness for example, it directed downward to the floor, the will indicate 50 on the one day, and upper strata of air being the warmest. 30 on the other. The action is great- The instrument placed on the floor est in general under a clear and trans- and directed upward, shews an imlucid atmosphere. But particular pression of warmth, but when placed winds blowing at different altitudes in the upper part and directed downseem to modify the effect.

ward, it shews an impression of cold. Mr Leslie then proceeds to inves- If the actions excited in the air of a tigate more closely the causes of these room are made thus apparent, much phenomena. It occurred to him, that more is to be expected from the disince pulses (which others call radia- versified condition of the different tions) are darted from such various strata of so vast a body as the atmosurfaces, and since the softness of the sphere. Taking it to the height of external coat and its humidity seem- two miles, including scarcely oneed vastly to augment their power, it third of the whole, the difference bewas possible that they might be like- tween the temperature of its extreme wise excited from a boundary of air boundaţies will amount to 20 degrees itself ; that the air probably thus of the centesimal scale, or 36 of Fahacted in two capacities in these phe- renheit. But the order is the reverse nomena; that is, both as an inter- of what takes place in a close room, medium for transmitting pulsations the air of the upper regions being inwhich it lias received from a body variably colder than that which is differing from itself in temperature, nearer to the surface of the earth. and giving out radiations of its own, As the higher strata of the atmodepending entirely on its particular sphere thus radiate cold downwards, temperature. The fact was ascer. so the lower strata must radiate heat tained by the following simple expe- upwards. To measure these would riment: In a room where a steady require the æthrioscope to be invertfire was kept up, the æthrioscope was ed, and furnished with a pendent difset on the inside of the window, and ferential thermometer. The instru. directed to the upper part of the op- ment in this form carried to the top of posite wall; the instrument stood at a lofiy mountain, and directed to the zero, because the temperature by plain below, would indicate a consiwhich it was surrounded, and that of derable impression of heat, nearly the places at a distance to which it proportional to the quantity of as. was directed, were nearly the same. cent. Perhaps on the summic of The window was then thrown open, Chimborazo, it might amount to and the instrument was surrounded twenty millesimal degrees; and in the by a body of cold air, in consequence same situation the upright athrioof which a motion in the fluid took scope might be expected to mark place, indicating an impression of an impression of cold from above, heat, evidently caused by the excess just so much diminished. If this of temperature of the remote air of last did not happen, it might be conthe room above that which was now sidered as giving countenance to the contiguous to the æthrioscope. The idea, that the giving out of caloric same thing is shown by the different by radiation from bodies exposed to indications of an æthrioscope, accord- the heavens, consists in the simple ing as it is placed on the floor of a escape of caloric into regions alto.


gether beyond the boundaries of the this instrument, employed by scientiatmosphere. No opportunity, howfic persons in different parts of the ever, has yet occurred on a large globe, will contribute to throw much scale, for making these interesting new light on the laws of temperaobservations. The ascent of a bal- ture, as regulating the phenomena loon would afford the readiest mode of the different regions of the atmoof verifying and extending the the sphere, and we may even hope that, ories suggested by the general as- as it becomes afterwards improved, pect of the facts.

it may open scenes altogether new The inverted æthrioscope likewise in the interesting but intricate and discovers the quality and measure of difficult science of meteorology. the radiations (or pulses, as Mr Leslie denominates them) which are projected from the ground. These, as ASTRONOMICAL OBSERVATIONS MADE measured within short distances in FOR DETERMINING THE FIGURE the air, are very feeble, seldom in this climate exceeding three or four degrees. In the progress of a bright The improvements made in astroday, as the ground grows warmer nomical observation, in consequence than the air, it excites hot pulses: of the high perfection to which astrobut, as the sun declines, the effect nomical instruments have arrived, gradually diminishes ; till this again has gradually led, and still leads to returns, increasing with a contrary the solution of important scientific character, when the surface of the problems, which at no distant period earth has become relatively colder. appeared to be beyond the limits of

Another effect we may also ex- human power. The coincidence of pect to find, depending on the si- various favourable circumstances con. tuation in which this instrument is tributes to give daily accessions to placed in a clear night, when the the knowledge which the world posground becomes cooled by radiation, sesses of the laws of nature, among that the æthrioscope will shew the which, none of the least is the comost powerful impressions of cold operation of scientific men embodied when held a little way from the in regular societies, by which extenground, and that, when it is placed on sive communications are maintained, the surface, it will indicate the most and the task of investigating nature powerful impressions, when placed on so subdivided as to admit of being a portion of the surface which is the prosecuted with undeviating closeleast radiating, and consequently the Dess and deliberation in each of its least cooled, because here the bulb, parts, by numerous individuals. Armwhich is not sentient, will partici- ed with all these advantages, some pate less than in another situation enlightened men have been lately in any cooling effect communicated employed in imparting to different by the conducting quality of the sur. subjects in astronomy, a precision face, so that the difference between which they had not previously atthe two bulbs of the differential ther- tained. It is our duty to notice the mometer will be the greater, and exertions which have been made in these differences are the degrees the last year, 1818, by M. Biot, of which that instrument, in the form of Paris, to measure an arc of the methe athrioscope, is fitted to indicate. ridian, of which he himself has pub

We cannot entertain a doubt, that lished a short but very interesting account. The determination of the of every planet, combined with the size and figure of the earth,--the centrifugal force of its rotatory mo. measurement of gravity at its surface, tion. He took them as in a fluid the connexion of these phenomena state, and shewed how to calculate with the interior construction of the the flattening of a planet of a homoglobe, with the disposition of the geneous mass, according to the instrata, and the laws of their densities, tensity of the gravity at its surface, are to be numbered among these long and the quickness of its rotation. enduring questions which learned so- This theorem as applied to the earth cieties alone could propose to en- gave a variation of gravity but little counter and resolve. The first exact differing from that observed by Richmeasurement of a degree of the ter- er, though somewhat slighter, shewrestrial meridian was made in France ing that the strata of the earth beby Picard in 1760. Newton avail- came denser as we penetrate from ed himself of it in order to establish the surface to the centre, a doctrine the law of universal gravity. Two since demonstrated by Clairault. years after this, Richer, who was em- More extensive measurements, howployed by the Academy of Sciences, ever, were thought requisite. An on a mission to Cayenne, for pur- accession of accuracy was expected poses of astronomical research, dis- to be obtained from the measurement covered that his clock, which at Paris of the complete arc which traverses beat the seconds gradually, went more France from Perpignan to Dunkirk, slowly as he approached the equator, a measurement intended at the time and that it again went quicker by to serve as a sort of axis to a general the same gradation in returning to- map of France, with the execution wards the north, so as to resume

of which Colbert had intrusted the exactly its original motion at the Academy. But in the imperfect state point of his departure. This was of the instruments and astronomical known to arise from the different in. methods of that period, the arc ittensity of the action of gravity in self was too short to make the influthese different parts of the earth’s ence of the fattening distinctly persurface; for they had just discover- ceptible ; and the small variations in ed that the quickness of the oscilla- the lengths of the degrees being tion of a pendulum augments or di- easily lost in the errors of the obserminishes with the force of gravity vations, the differences which were which causes its motion. The ob. found were in such a direction as servation of Richer thus proved that would have led to the inference of the intensity was different in differ- an elongation, instead of a flattening ent latitudes, increasing in going from at the poles. The Academy perthe equator to the pole. Newton, in ceived that the question could not be his Principia, connected all these clearly decided, without measuring results with the law of attraction. two arcs of the meridian, near the He shewed that the variation obser.' equator, and near the poles, from ved in gravity, disclosed a flattening which greater differences might be of the earth at the pole, a circum- brought out. In 1735, Bouguer, stance which is observable also in Godino, and La Condamine, went to the form of Jupiter, Saturn, and the America, where they joined the Spaother planets which turn on an axis. nish commissioners. Some months He attributed this flattened form to after, Clairault, Maupertuis, and La the uniform attraction of the portions Mounier, departed for the north.

The results of these expeditions put attended to. Borda invented for this the flattening of the earth beyond a experiment a method surpassing in doubt, but did not fix its absolute exactness everything previously amount. The degree of Peru, com- suggested, and never since exceedpared with that of France, gave a ed. slighter flattening than if the earth It was afterwards thought that the were homogeneous : the operation of arc of the meridian might be con, Lapland indicated a greater. In this tinued a good many degrees to the uncertainty, the lengths of the pen- south across Catalonia, and even produlum, which they were careful to longed to the Balearic Isles, by means measure, agreed with the flattening of a very large triangle the sides of deduced from the operation of the which should join these isles to the equator ; but the exactness of these coast of Valencia. Méchain having measurements, especially in the ope- surveyed and measured the first triration of Lapland, was not such as angles, died in a small town of Vacould enable them to solve the dif- lencia, and Messrs Biot and Arago ficulty. The proceedings of the best were charged with the completion observers could not be more accu- of the work, along with the commisrate than they were; but the instru- sioners of the King of Spain. They ments then constructed laboured un- happily succeeded, though Arago der imperfections.

was subsequently exposed to danger After an interval of fifty years, as- and detained in captivity for some · tronomical instruments having be- time before his return to France. come more perfect, and the methods The results confirmed those of the of observation more precise, the Aca. arc of France. They also measured at demy resumed these great operations their most remote station, the length with all the means which could in- of the seconds pendulum, after the sure their success. In order to give method of Borda, Biot, and Matthem greater importance, it was re- thieu, and repeated the same operation solved to take ihe very size of the on different points of the arc comearth as thus determined for the fun- prised between Perpignan and Dundamental element of a system of ge- kirk. These observations gave for neral, and uniform measures. The the fattening of the earth a value organization of the Academy was de- almost equal to that which M. de ranged, while its name was discon- Lambre had already obtained, by tinued, during the stormy part of the comparing the arc of France and French Revolution. But in the midst Spain with the degrees of the equaof the political confusion, Messrs de tor, calculated with fresh pains ; also Lambre and Méchain, furnished with with the degree of Lapland, which new instruments which Borda had in- Mr Swanberg, an able Swedish asvented for them, began and con- tronomer, had corrected by new obtinued, often at the risk of their lives, servations, and finally, with an arc the most extended and exact mea- of many degrees which Major Lambsurement of the earth which had ever ton had measured with great accubeen undertaken.

Although they racy in India. had many difficulties to encounter, Verified by these combined coincithey concluded it as well as they dences, the arc of France and Spain ould have done in the bosom of the acquired a farther claim to become L'ost profound peace.

The mea. the foundation of a standard of meaaurement of the pendulum was also These operations acquired


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