iron arising from its rotation. 379 
It appears, from these observations, that, when the plate 
revolves in the plane of a secondary to the equator and 
meridian, 
1st. The deviation due to rotation is a maximum when the 
centre of the plate is in the equator. 
2d. It decreases as the plate approaches the pole, and is o 
between the latitudes 50° and 60°, apparently very nearly at 
55° ; and from this point it increases till it attains a maximum 
in a contrary direction at the pole. 
3d. At the south pole and on each side down to the lati- 
tude 55°, the deviation of the south end of the needle, due to 
rotation, is in the direction of the ?iorth, or lower edge of the 
plate ; or, from the south pole down to the latitude 55®, the 
south end of the needle moves towards the plate, when the 
inner edge of the plate moves from the south pole, 3 x\dfrorn 
the plate when the inner edge moves towards the south pole. 
4th. From the equator towards either pole as far nearly 
as the latitude 55®, the south end of the needle moves in the 
direction of the south edge of the plate ; that is, it moves 
towards the plate when the inner edge of the plate moves 
towards the south pole, and from the plate, when that edge 
moves /rom the south pole ; also the north end of the needle 
moves towards the plate, when the inner edge moves towards 
the north pole, and from the plate, when that edge moves 
from the north pole. Consequently towards whichever pole 
the inner edge moves, the corresponding end of the needle 
will move towards the plate from the equator to the latitude 
of 55° nearly, and the contrary will take place from the lati- 
tude to the pole. 
The observations which I made with the plate on the north 
MDCCCXXV. 3 D 
