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.

    89/280 (page 63)
    servations on this head are neither so numerous nor so accurate as those of the variation. It seems at present to be about 72° at London, according to Mr. Cavauto; and there is reason to suppose, it is not many degrees different in any part of Eng- land ; for want of proper instruments I have not been able to ascertain it at this place. Besides the annual change in the variation of the needle, there is a daily change, or variation of the variations. According to Mr. Canton, who made a series of observations on the daily variation for a long time, the north pole of the needle moves gradually westward till 2 or 3 P. M. and then re- turns gradually to its former station ; the mean daily variation in winter is about 7’, and in summer about 13%’. He moreover observed, that the needle was disturbed when an Aurora borealis was in the atmosphere. I have myself made a like series of observations for some months, and find them in general to agree with his; but as it is not necessary for my purpose to relate the result of them, any further than what is contained in the subsequent pages, I shall not detain the reader longer on the subject.