C
magnetic north or south of the earth, the magnetic inclination
shows how far a place is from the magnetic poles. All places,
on which the needle stands horizontally (the neutral line of the
earth as a magnet) form the magnetic equator for and lines con
necting places in which the dipping needle makes equal angles
with the respective magnetic meridian are called isoclinic lines.
At the magnetic poles the dipping needle stands vertical.
Remark. It is generally supposed that Robert Norman (1576) dis
covered inclination; but 33 years before him George Hartmann, a curate
in Nürnberg, was acquainted with it. He also discovered the law, that
poles of the same name repel and poles of contrary names attract each
other.
§ 248. The magnetic north-pole was found by Sir James
Ross in 96° 43′ west longitude and 76° northern latitude; of
the southern we only know, that it is about 154° east longitude
and 75½° south latitude.
§ 249. Inclination as well as declination is subject to
variations. In London and Berlin both are continually decreasing. 416. Besides this secular variations, there are annual
and diurnal variations, and calling all this regular variations,
we may observe also extraordinary variations, caused by the
Aurora borealis, earth-quakes and volcanic erruptions.
§ 250. It is supposed that all these phenomena are caused
by two magnetic fluids, which before magnetisation mutually
neutralize each other and separated by a stronger force each of
them repels itself and attracts the other. One is called the
north or boreal (positive) fluid, the other the south or austral
(negative) fluid. Of course this is only a hypothesis, and as
the chapter on electricity will show, a very doubtful one. The
most powerful means of imparting magnetism is:
