Balloon Ascents of Gay-Lussac and Biot
At the commencement of 1804 Laplace proposed to the members of he French Academy of Sciences that balloons should be employed for the purpose of solving certain physical problems, adding that, as the government had placed funds at their disposal for the prosecution of useful experiments, he thought they might be well applied to this kind of research. The proportion was supported by Chaptal the chemist, who was then minister of the interior, and accordingly the necessary arrangements were speedily effected, the charge of the experiments being given to MM. Gay-Lussac and Biot.
The principal object of this ascent was to determine if the magnetic force experienced any appreciable diminution at heights above the earth's surface, De saussure having found that such was the case upon the Col du Geant. On August 24, 1804, MM. Gay-Lussac and Biot (the former eminent as a chemist and the latter as a natural philosopher) ascended from the Conservatoire des Arts at ten o'clock in the morning. Their magnetic experiments were incommoded by the rotation of the balloon, but they found that, up to the height of 13,000 feet, the time of vibration of a magnet was appreciably the same as on the earth's surface. They found also that the air became drier as they ascended. The height reached was about 13,000 feet, and the temperature declined from 63° Fahr. to 51°. The descent was effected about half-past one, at Meriville, 18 leagues from Paris.
In a second experiment, which was made on September 16, 1804, M. Gay-Lussac ascended alone. The balloon left the conservatoire des Arts at 9.40 A.M., and descended at 3.45 P.M. between Rouen and Dieppe. The chief result obtained was that the magnetic force, like gravitation, did not experience any sensible variation at heights from the earth's surface which we can attain to. Gay-Lussac also brought down air collected at the height of nearly 23,000 feet, and on analysis it appeared that its constitution was the same as that of air collected at the earth's surface. At the time of leaving the earth the thermometer stood at 82° Fahr., and at the highest point reached (23,000 feet) it was 14° .9 Fahr. Gay-Lussac remarked that at his highest point there were still clouds above him.
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