London, June 17, 1758.
IN a former letter I mentioned the experiment for cooling bodies by evaporation, and that I had, by repeatedly wetting the thermometer with common spirits, brought the mercury down five or six degrees. Being lately at Cambridge, and mentioning this in conversation with Dr. Hadley, professor of chemistry there, he proposed repeating the experiments with ether, instead of common spirits, as the ether is much quicker in evaporation. We accordingly went to his chamber, where he had both ether and a thermometer. By dipping first the ball of the thermometer into the ether, it appeared that the ether was precisely of the same temperament with the thermometer, which stood then at 65; for it made no alteration in the height of the little column of mercury. But when the thermometer was taken out of the ether, and the ether, with which the ball was wet, began to evaporate, the mercury sunk several degrees. The wetting was then repeated by a feather that had been dipped into the ether, when the mercury sunk still lower.
We continued this operation, one of us wetting the ball, and another of the company blowing on it with the bellows, to
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Publication information: Book title: The Ingenious Dr. Franklin:Selected Scientific Letters of Benjamin Franklin. Contributors: Nathan G. Goodman - Editor, Benjamin Franklin - Author. Publisher: University of Pennsylvania Press. Place of publication: Philadelphia. Publication year: 1931. Page number: 165.
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