Meteorological observations and essays / By John Dalton.

  • John Dalton
Date:
1834
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Licence: Public Domain Mark

Credit: Meteorological observations and essays / By John Dalton. Source: Wellcome Collection.

    216/280 (page 190)
    the condensation of vapour, yet when the pressure is removed, evaporation is promoted ; for under the receiver of an air-pump we find that the vapour from the wet leather rises ag fast as it can be pumped out, when the rarefaction has proceeded to a certain degree. In order the more to illustrate and confirm the notion of vapour here laid down, we shall now attempt to explain several facts, which have been considered as involving difficulties, and we believe some of them have never been accounted for by others. Dr. ALExanpeR, in’ his Haperimental Essays, page 102, informs us, that from some experiments he was induced to think, that blowing upon the bulb of a thermometer with a pair of hand-bellows would cool it, but upon trial found it was always heated one or more degrees by the operation.— Now, if a thermometer that has just been dipped in water of the same temperature as the air, be blown with a pair of hand-bellows as above, it will be cooled several degrees. These two facts I have proved frequently, from experiment.—Again, Dr. Darwin’ (see the note, page 129) found that air having been for some time condensed, upon rush- ing out against the bulb of a thermometer, cooled it several degrees, and a dew was deposited upon the bulb. The reason of these apparently discordant facts may be explained thus : the condensation of vapour in a pair of hand-bellows will precipitate a portion