371 
iron arising from its rotation. 
Here we find, directly contrary to what took place when the 
plane of the plate was a tangent to the sphere, that the devi- 
ation due to rotation increases from the equator to the pole 
where it is a maximum. In this case, however, as in the 
other, the deviations are very nearly equal at equal distances 
on each side of the equator ; so that, as before, it appears 
that the horizontal needle was affected by the rotation of the 
plate, not according to the situation of the centre of the plate 
with respect to the poles and equator of the horizontal 
needle, but with respect to the poles and equator of an ima- 
ginary dipping needle passing through the centre of the 
horizontal needle. 
t 
With regard to the direction of the deviation due to rota- 
tion, it appears, that when the centre of the plate had north 
latitude, the north end of the needle deviated in the direction 
of the motion of the plate’s inner edge; and when it had south 
latitude, the north end deviated in a contrary direction to that of 
the inner edge of the plate, and therefore the south end devi- 
ated in the direction of the inner edge : so that, the end of the 
needle of the same name as the latitude, always deviated in the 
direction of the motion of the plate’s inner edge. 
Let us compare this with the inference we have drawn 
from the observations in Table I. viz. that when the centre 
of the plate is in the meridian, and its plane a tangent to the 
sphere, the north end of the needle, by the rotation of the 
plate, deviates in the direction of the motion of the south 
edge, and the south end in the direction of the north edge of 
the plate ; that is, either end of the needle deviates in a direc- 
tion contrary to that of the motion of the edge of the plate 
nearest to the pole of the sphere of the same name as that 
MDCCCXXV. 3 C 
