It has been an opinion
pretty generally received among philosophers, that the atmosphere of
America is more humid than that of Europe. Monsieur de Buffon makes this
hypothesis one of the two pillars whereon he builds his system of the
degeneracy of animals in America. Having had occasion to controvert this
opinion of his, as to the degeneracy of animals there, I expressed a
doubt of the fact assumed, that our climates are more moist. I did not
know of any experiments, which might authorize a denial of it. Speaking
afterwards on the subject with Dr. Franklin, he mentioned to me the
observations he had made on a case of magnets, made for him by Mr.
Nairne in London. Of these you will see a detail in the second volume of
the American Philosophical Transactions, in a letter from Dr. Franklin
to Mr. Nairne, wherein he recommends to him to take up the principle
therein explained, and endeavor to make an hygrometer, which, taking
slowly the temperature of the atmosphere, shall give its mean degree of
moisture, and enable us thus to make with more certainty a comparison
between the humidities of different climates.
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