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what has already been observed is sufficient to shew us that the warmer the water is, the more it dilates the ivory (though we saw that the mercury rose in the hygrometer after having sunk for a moment). From hence, I fancy may be drawn this general consequence, already indeed foreseen, namely, that in an equal acting quantity, the warmer the humor is, the more it separates the particles of those bodies which it pervades.

107. I say, in an equal acting quantity, and this is one of the object which will probably furnish us with a variety of most useful knowledge, at the same time that it is most likely to give the greatest exercise to the genius and attention of natural phi- losophers. The forementioned experiment proves, that the warmer the water is, the more it dilatates the ivory pipe of the hygrometer, and the fame thing I make no doubt happens with the discrete humor. On the other hand, the evaporation, being certainly greater in summer than in winter, there must of course be more vapours in the air, in the first of these seasons than in the latter. These then, as it appears, are the two circumstances most likely to make the hygrometer fall in summer ; a greater degree of humor in the air, and an encrease of heat. And yet l have already experienced that the mean height of the hygrometer is greater in summer than in the other seasons I found my first hygrometer, which was made in winter, too short in the summer; but it would be of a sufficient length now that we are in autumn. The mean height of the four new ones is already (the beginning of Novem-

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