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.

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    more frequent now than formerly in these parts ; if the earth’s magnetic poles be like the centres of the aurora, as the phenomena indicate, it is plain the aurora must move along with them, and appear or disappear at places, according as the magnetic poles approach or recede from them ; and hence it may be presumed that the earth’s magnetic pole in the northern hemisphere is nearer the west of Europe in this century than it was in the last or preceding.—The observations upon the dip of the needle, however, if they have been accurately made, seem to indicate the approach of the magnetic pole to have been very little ; the dip at London, accord- ing to Mr. Cavaxio, was 71° 50’ in 1576, and 72° 3 in 1775; but there is reason to suspect the ac- curacy of the instruments at so early a period as 1576 ; besides, we do not know in what proportion the dip of the needle keeps pace with the approach of the pole. It may perhaps be necessary here, before the subject is dismissed, to caution my readers not to form an idea that the elastic flued of magnetic matter, which I have all along conceived to exist in the higher regions of the atmosphere, is the same thing as the magnetic fluid or effluia of most writers on the subject of magnetism. This last they consider as the efficient cause of all the magnetic phenomena; but it is a mere hypothesis, and the existence of the effluvia has never been proved. My fluid of magnetic matter is, like magnetic steel, a substance possessed of the properties of magnetism, or, if