ongated. Immediately below the reservoirs ther plate brightly coated with silver. The ould be arranged horizontally on one of the remaining constantly exposed to the solar othermeters of an arbitrary scale. hygrometers. also of pumice, wet with sulphuric acid, for eid of the air. The air should be drawn in of one litre (1.760 pint) accurately gauged. city, furnished with stop-cocks of steel, for ons. These balloons, enclosed in tin boxes, fair before the ascent. I. Walferdin, which should be enclosed in a is best that this instrument should be placed rral and Bixio, since the control of the pernute instrument imparts considerable value d affords a triumphant reply to objections the human mind, always oppose themselves ely verified by new experiments made under moreover, of the ascension of the balloon to below-40°, the point of congelation for -e thermometers of alcohol or sulphuret of of the thermometric scale, so that the obsera circumstance which has ceased to be con st stated, that I would recommend also the 1. Regnault, and intended to indicate the consequently the maximum of elevation to his apparatus should be enclosed in a tin case gs. The lid of this case should be secured ometer. as I have described, Astronomie populaire, e declination, inclination, and intensity of nner as not to be affected by the movements nt, as has been observed by MM. Biot, Gay as to be capable of indicating at once the city of different atmospheric strata. ascension, observers will be able to embrace dy, or use successively and opportunely so should, on each occasion, limit himself to a s. It is only in a series of aeronautic expen be made corresponding to the great number a of the terrestrial atmosphere presents for in the principal terrestrial obse the aeronauts propose to under of the British Association, in : night derive from aerostatic as Lubbock, Robinson, Sabine, W by MM. Barral and Bixio, wh noticed in the higher regions time on the surface of Europe. Barometric observations in means of a formula which we elevation to which balloons asce been reduced into the usual tal des longitudes. The considera his analysis led him to emplo determination Ramond had a measurements of the height of trigonometric measurements. allel of 45°, and upon mountai there is nothing to prove that is susceptible of being applied heights, and made in other lati directly, by observations made known distances, the heights results obtained with the barom will present numerous difficul success, because the balloons directions which will not pern any advantage. But the probl importance the sacrifices which solution. III.-AERONAUTIC VOYAGES At the moment of the ascens The two aeronauts thought t of the magnetic needle to be and that consequently the mag UI མ་་་ན YuyaSUབ, LHÇIV བIVསIས པ༦ མཧསཅ) at ICཧS LIouI བVས༴ ༦ IVuI, pal terrestrial observatories, observations analogous to those which s propose to undertake. This was advised in 1841 by a committee sh Association, in a report relative to the advantages which science e from aerostatic ascensions, a report signed by Brewster, Herschel, obinson, Sabine, Whewell, and Miller, and the advice was observed rral and Bixio, who were thus enabled to connect the phenomena he higher regions of the air with those which occurred at the same surface of Europe. ric observations in connexion with those of temperature yield, by formula which we owe to the genius of Laplace, the measure of the › which balloons ascend above the level of the sea. This formula has ed into the usual tables which are found in the Annuaire du bureau des. The considerations on which the illustrious geometer founded is led him to employ in his admirable formula a coefficient whose ion Ramond had arrived at, by comparing a great number of the ents of the height of mountains taken with the barometer with their tric measurements. Now, as Ramond operated chiefly under the par°, and upon mountains whose elevation scarcely reached 3,000 meters, othing to prove that the undetermined coefficient of Laplace's formula ible of being applied to the measurement of much more considerable ind made in other latitudes. It would not be superfluous to measure by observations made from several astronomical stations situated at istances, the heights to which aeronauts attain, and to compare the btained with the barometric determinations. No doubt these operations ent numerous difficulties, and may be not unfrequently tried without because the balloons may disappear in the clouds or be carried in as which will not permit the terrestrial telescopes to follow them with antage. But the problem to which I here call attention merits by its nce the sacrifices which may be encountered in giving it a satisfactory -AERONAUTIC VOYAGES OF LHOEST, ROBERTSON, AND SACHARoff. first aeronautic voyage to which science was indebted for some useful ions was that performed at Hamburg, July 18, 1803, by the physicist, son, accompanied by his countryman, Lhoest. They remained suspended air five hours and a half, and descended at Hanover, twenty-five leagues from the place of departure. he moment of the ascension the barometer on the earth stood at 28 inches, e thermometer at +16° Reaumur; at the greatest height to which they ed the barometer showed 12.4 inches, and the thermometer-5°.5 Reaumur. observations, reduced to metric and centigrade measurements, give 758 meters for the barometric height, and +20° for the temperature at starting; millimeters and-6°.9 at the highest point reached. Hence, according to ormula of Laplace, we deduce 6,831 meters as the maximum height to h the balloon ascended. he two aeronauts thought that at that height they observed the oscillations e magnetic needle to be much less rapid than at the surface of the earth, that consequently the magnetic intensity diminishes rapidly as the elevation lours 45 minutes p. m., and descended at a distance of about 20 leagues. At the ood at 30 inches, and the thermometer at on the two instruments indicated respectWe conclude from these observations that ature were, at the point of departure, 812.1 st elevation, 595.5 millimeters and +59.6; st point reached was 2,703 meters. MM. le to make regular magnetic observations, t the needle of declination had ceased to > was elevated about 10 degrees, its south > amount towards the earth. BIOT AND GAY LUSSAC. ons made on the Col du Geant at a height Duration of 5 oscillations. giving 35 seconds for the duration of five differences are too small to allow of any 6,182 64 From these observations, whic ferences, Gay Lussac drew the undergo sensible variations up to regard to this he thus expresses drawn from our experiments ma remember that we have not been of the magnetic needle. But wh a horizontal needle to oscillate i Erection of the magnetic force i of the angle of inclination of t arrived at cannot fail to be dra varied, the total force cannot that the magnetic force may var the same relation to the cosine of We have, moreover, in support d nation which was made at the h at that elevation the inclination conclusion was logical at an epoc given place and under given circ magnetic needle is influenced by thermometer of Gay Lussac ha noticeable changes in the magnet of the instruments and the scien exact solution of the problem present this problem is still unsol The principal result of the ae Constant composition of the atmo illustrious physicist had the good regions, and to give an analysis d fied by new experiments conduct has discovered during half a cen Another fact, no less importa found between the temperature 22 s se observations, which do not present sufficiently appreciable dify Lussac drew the conclusion that the magnetic force does not sible variations up to the greatest heights which we can attain. In is he thus expresses himself: "The consequence which we have our experiments may seem a little too precipitate to those who hat we have not been able to make observations on the inclination netic needle. But when it is remarked that the force which causes l needle to oscillate is necessarily dependent on the intensity and the magnetic force itself, and that it is represented by the cosine le of inclination of this last force, the conclusion which we have cannot fail to be drawn, that, since the horizontal force has not total force cannot have varied, unless one chopses to suppose nagnetic force may vary precisely in an opposite direction, and with -elation to the cosine of its inclination, which is not at all probable. moreover, in support of our conclusion, the experiment of the incliich was made at the height of 3,902 meters, and which proves that evation the inclination did not vary in a perceptible degree." This a was logical at an epoch when it was not generally known that at a ce and under given circumstances the duration of the oscillations of a needle is influenced by its temperature. Now, the depression of the eter of Gay Lussac had been sufficiently considerable to produce e changes in the magnetic needle. We see that, in the imperfect state struments and the science in 1804, it was impossible to arrive at an lution of the problem which the Institute had in view. Even at his problem is still unsolved. principal result of the aeronautic voyage of Gay Lussac relates to the composition of the atmospheric air to a height of 7,000 metres. The us physicist had the good fortune to bring the first air from those high and to give an analysis of it, whose accuracy has been uniformly verinew experiments conducted with the improved processes which science Covered during half a century. her fact, no less important, is the wide difference which Gay Lussac between the temperatures below and at the great height to which he very considerable in high regions of nstruments whose indica ions are so little is impossible to deduce precise conclu st value the recitals of physical sufferings elevated strata of air; he expresses himand simplicity: "Arrived at the highest above the mean level of the sea, my respiat I was still very far from experiencing a Id induce me to descend. My pulse and and, breathing thus rapidly in an air of prised at having the throat so dry that it ons of Biot and Gay Lussac are the first success as regards the solution of scientific OF BARRAL AND BIXIO. -o aeronautic voyages, by the last of which, th unforeseen results of great importance. Sciences an account of the first excursion of sed myself in nearly the following terms: eived the idea of ascending to a great height ed scientific instruments of the present day, mena still imperfectly known. It was prodecrease of temperature with the height; the ; to ascertain whether the chemical composithroughout; the portion of carbonic acid at the calorific effects of the solar rays in the with these same effects observed on the surhether there arrives at a given point the same points of space; whether the Fight reflected s not polarized, &c. so interesting an expedition had been presion by M. Regnault. Never has the love of -re disinterestedness. M. Walferdin furnished meters. The explorers were, besides, provided graduated, for determining the height at which ade. All the preparation of the balloon to M. Dupuis I himself by twenty-eight aerial voyages. the garden of the Observatory of Paris. The June 29, 1850, at 10 hours 27 minutes in the een filled with pure hydrogen gas procured by n iron. culation, the explorers might now have expected or 12,000 meters, supposing the upper strata of with received theoretical ideas. peared in the clouds, and it The dilated balloon press Consulting the barometer They fell, at 11 hours 14 m tunately soft, in the commun vine-dressers ran to their he feet and hands to the stems d ble the horizontal movement rendered them. From a voyage performed could derive but a very small might have been expected; y established, by decisive experi that the bed of clouds which t ness, and that, notwithstandin and sky, the decrease of tem verified by Gay Lussac in l cloudless sky. From the bar at the Observatory of Paris, balloon was torn, the height computation that the upper £ height of 4,200 meters. The following numbers comp At the moment of departure tl marked 753 millimeters, and t the wind was west-southwest, & 29 minutes the voyagers pen dense mist, which deprived 1 minutes the barometer of the |