Meteorological observations and essays / By John Dalton.

  • John Dalton
Date:
1834
Catalogue details

Licence: Public Domain Mark

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

    123/280 (page 97)
    country, if it displace an equal bulk of air specifi- cally heavier than the vapour: and in like manner, rain at any place may not diminish the weight of the air there, because the place of the vapour may be occupied by a portion of air specifically heavier. It should seem therefore, that when the air over any country is cleared of vapours, &c. the barome- ter ought to be higher than usual, and not lower.— But we shall now proceed to state our own ideas on the subject. It appears from the observations, (see table, page 15,) that the mean state of the barometer is rather lower than higher in winter than in summer, though a stratum of air on the earth’s surface always weighs more in the former season than in the latter ; from which facts we must unavoidably infer, that the height of the atmosphere, or at least of the gross parts of it, is less in winter than in summer, conformable to the table, page 80. There are more reasons than one to conclude that the annual variation in the height of the atmosphere, over the temperate and frigid zones, is gradual, and depends in a great measure upon the mean tem- perature at the earth’s surface below; for clouds are never observed to be above four or five miles high, on which account the clear air above can receive little or no heat, but from the subjacent regions of the atmosphere, which we know are in- fluenced by the mean temperature at the earth’s surface ; also, in this respect, the change of tem- perature in the upper parts of the atmosphere must, )