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hammer upon the plain, in fine weather, came off of itself upon the top of the mountain. When this happened, the thermometer, which I called common, though exposed to the fun, was only three degrees above 0; while on the plain it was at 18 in the shade. This phaenomenon, joined with several others I observed at the same time, confirmed me in my opinion, that one of the reasons why the upper parts of the atmosphere have less heat than the lower, is, that they contain less humor.

77. With this notion, it became a very interesting inquiry to know the different degrees of humidity habitual to the different heights of the atmophere. Of course therefore this was the first observation I thought of, as soon as I bad added an hygrometer to the other instruments contained within the box of my portable barometer. I undertook therefore to ascend Buet (the name or that high mountain) a second time. My companions in this expedition were Mr. Dentan, a very intelligent young philosopher, and my brother, who, having assisted me in all undertakings of any difficulty, had been a witness of that fact which was the object of my present researches.

78. At our setting on the 29th of last August, the hygrometer was at 86 in my apartment, and the barometer at 27 p. 1 line. We were in hopes of fine weather, because it is generally fair in this country when the barometer at Geneva is above 27 French inches Soon after we set out, we began to perceive that the power of the fun was greater than might have been expected for the season. From this circumstance I concluded that the barometer must

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