Johnson's natural philosophy and key to philosophical charts : illustrated with 500 cuts; being reduced photographic copies of all the diagrams contained in the author's philosophical series of indestructible school charts ; for the use of schools and families (1878)
ation is calledthe dip. The dip, like the declination, is subject to continual and progressivechanges. At London, in 1576, it was 71 50; in 1723 it was at itsmaximum, being 74° 42, while now it is only 68° 15; showing it hasdecreased about 3 per annum for the last hundred and fifty years. 344… … If a needle, free to move vertically, be placed at the magnetic equator,F, its two poles will be equally attracted by the magnet, and the needlewill coincide with the horizon, shown by the dotted line; its real northpole standing in the direction of the south pole of the magnet. If the needle be…
Physics · Astronomy
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