or increase in the magnetic force, inclination of the magnetic needle, increase of heat of the solar rays, fainter colours in the spectrum, influence of rarefaction of the air on the human body, as well as some other chemical and philosophical experiments. A height of about two miles was reached, and many interesting observations were made, but since the instruments were not easily used in the basket of the balloon, the results were unsatisfactory and required repetition to be conclusive. The Academy of Sciences of Paris now took up the investigation with the special object of proving whether the magnetic force decreased as Robertson in a balloon and De Saussure in the Alps had supposed. Two young physicists, Biot and Gay-Lussac, were chosen to carry out the investigations. They ascended from Paris on August 24, 1804, provided with all necessary instruments, but the balloon was too small to rise higher than 13,000 feet. Gay-Lussac ascended alone to a height of 23,000 feet on September 16, 1804, in a balloon filled with hydrogen. His observations confirmed those which he had made with Biot, that there was no change in the magnetic force, and from samples of air collected he proved that the chemical constitution of the air is invariable. His observations of temperature seemed to confirm the theory of a decline of temperature of 1∞ in 300 feet of elevation. The air was found to be very dry, and Gay-Lussac noticed that at the highest altitude the clouds were still far above him. Passing over several notable ascents in other countries, it was not until 1850 that scientific ballooning was begun again in the land where the balloon originated. Then MM. Barral and Bixio made two ascents from Paris in rainy weather to the heights of 19,000 and 23,000 feet respectively, although they had expected to attain twice these altitudes. Their most interesting observations were the great thickness of the cloud mass, which in one case amounted to 15,000 feet, and the sudden fall of temperature in it from +15∞ to -39∞. Some curious optical phenomena were connected with the floating ice crystals, and although the light of the sky was found to be strongly polarized, the light reflected from the clouds was not polarized.