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.

    102/280 (page 76)
    in ascending above the earth’s surface, nearly in an arithmetical progression, and at the rate of 1° for every hundred yards. Experience proves this, as far as to the summits of the highest mountains, which is about 38 miles; and hence it may be in- ferred to be so above that height. The great heat in the torrid zone rarefies the air, by increasing its elasticity ; consequently the equi- librium of the atmosphere is disturbed. The rare- fied air ascends into the higher regions, where, meeting with little resistance, it must flow north- ward and southward ; the pressure upon the north- ern and southern regions is thus increased, and a current must set in below, towards the equator, to restore the equilibrrum.—Hence, the higher tem- perature within the torrid zone swells the atmo- sphere there, and raises it, or at least the gross parts of it, to a much greater height than else- where ; whilst in the frigid zone it is contracted by cold.—This is the effect of the different tempera- tures at the earth’s surface ; but the increase of cold in ascending destroys the law of decrease in density above mentioned, and greatly contracts the height of the atmosphere, as deduced from such law; though this circumstance has perhaps no effect upon the figure of the atmosphere. Philosophers have attempted to find the height of the atmosphere by two methods; namely, by the duration of twilight, and by experiments upon the descent of the barometer on high mountains. The former determines the height about 45 miles, as follows :—the twilight disappears when the sun is