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.

    88/280 (page 62)
    and suffered to move freely both horizontally and perpendicularly, it will rest only in one position, namely, when in the plane of the magnetic meri- dian, and having its north pole pointing towards the ground ; the angle of deflection from the hori- zontal plane, is called the dip of the needle, and the needle itself in this case a dipping-needle ; its position is the proper and natural one of every magnet that is suffered to be guided solely by the magnetic influence. From this phenomenon, and others of the same nature, it is inferred, that the earth itself is a magnet ; whether its magnetism results from the united influences of the natural magnets it contains, or whether its magnetism may be in its atmosphere, is not certain; and as poles of unlike denominations attract each other, the south pole of the earth’s magnetism must be in the northern hemisphere, because it attracts the north pole of the needle. The variation of the needle is very different at different places of the globe, and even at the same place at different times ; in these parts it is at pre- sent westerly, and is increasing every year; the variation at London in 1580 was 11° 15’ E. in 1657 it was 0° 0’; at present, 1793, it is about 222° W. and increases nearly 10° each year. From the re- sult of several observations I find it to be 25° W. at this time, at Kendal. The dip of the needle too is very different at different places, and probably at the same place at different times ; but, for various reasons, the ob-