here, and as in the first figure; for so the
magnetick needle will remain in equilibrium. But in an oblique position of
the terrella, as in an oblique sphere, and in the second figure, the needle
dips obliquely at one end toward the near pole, but does not rest on the
pole, nor is its dip ruled by the pole, but by the body and mass of the
whole; for the {189} dip in higher latitudes passes beyond the pole. But in
the third position of the terrella the needle is perpendicular; because the
pole of the stone is placed at the top, and the needle tending straight
toward the body reaches to the pole. The cross in the preceding figures
always turns toward the boreal pole of the terrella, having been touched by
the boreal pole of the terrella; the cusp of the needle, having been
touched by the southern pole of the stone, turns to the south. Thus one may
see on a terrella the level, oblique, and perpendicular positions of a
magnetick needle. *

[Illustration]

* * * * *

CHAP. II.

Diagram of declinations of the magnetick needle, when
_excited, in the various portions of the sphere, and horizons_
of the earth, in which there is no variation
_of the declination_.

[Illustration]

{190} As aequator let A B be taken, C the north pole, D the south, E G
dipping-needles in the northern, H F in the southern part of the earth or
of a terrella. In the diagram before us all the cusps have been touched by
the true Arctick pole of the terrella.

Here we have the level position of the magnetick needle on the aequator of
the earth and the stone, at A and B, and its perpendicular position at C,
D, the poles; whilst at the places midway between, at a distance of 45
degrees, the crosses of the needle dip toward the south, but the cusps just
as much toward the north. Of which thing the reason will become clear from
the demonstrations that follow.

_* Diagram of the rotation and declination of a terrella_
conforming to the globe of the earth, for a
_latitude of 50 degrees north._

[Illustration]

A is the boreal pole of the earth or of a rather large terrella, B the
southern, C a smaller terrella, E the southern pole of the smaller
terrella, dipping in the northern regions[233]. The centre C is placed on
the surface of the larger terrella, because the smaller terrella shows some
variation on account of the length of the axis; inappreciable, however, on
the earth. Just as a magnetick needle dips in a r