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.

    116/280 (page 90)
    parallel is then as great as at 30° of south latitude, which is quite contrary to experience : in fact, they ought to have extended, in a greater or less degree, over the ocean, from the equator to the poles, and the summers have been more tempestuous than the winters, because the daily variation in heat is then greatest ; neither of which we find consistent with observation. The relative velocity of winds may be best ascer- tained by finding the relative velocity of the clouds, which, in all probability, is nearly the same as that of the winds; the velocity of a cloud is equal to that of its shadow upon the ground, which, in high winds, is sometimes a mile in a minute, or sixty miles an hour; and a brisk gale will travel at the rate of twenty or thirty miles an hour.—It may be imagined, that the relative velocity of winds should be continually upon the increase, by reason that their causes are constantly in action, and not for a mo- ment only ; but the resistance which a current of air meets with from the atmosphere itself, and from objects upon the earth’s surface, must be very con- siderable ; the increase or diminution of the relative velocity of a wind will therefore depend upon the proportion between the active causes and the re- sistance. ; The economy of winds, an illustration of which we have been here attempting, is admirably adapted to the various purposes of nature, and to the general intercourse of mankind :—had the sun re- volved round the earth, and not the earth on its