372 Mr. Christie on the magnetism oj 
end. Now, if from the position which the plate had in the 
last experiments, namely, its plane passing through the cen- 
tre of the needle, it be conceived to revolve about its dia- 
meter, which is perpendicular to the plane of the meridian, 
until its plane be a tangent to the sphere, the direction of the 
revolution about this diameter being of the inner edge towards 
the pole of the same name as the latitude of the plate's centre, 
the inner edge will become the edge of the same name as the 
end of the needle, which, in its first position, according to 
our inference from the last observations, deviated in the 
direction of its rotation ; but according to the inference drawn 
from Table I. the end of the needle of the same name as this 
edge will, in the new position, deviate in a direction contrary 
to that of its rotation ; so that the rotation of the plate being 
in the same direction in both positions, the deviations by rota- 
tion will be in contrary directions in the two cases ; and con- 
sequently, between the two positions, the plane of the plate 
must have passed through one in which the rotation would 
produce no deviation. If we conceive the plate to come into 
the position of the tangent plane by revolving about its dia- 
meter in the opposite direction, that is, by the inner edge 
moving towards the pole of a contrary name to the latitude, 
the inner edge will become the edge of the contrary name 
to the end of the needle, which in the first position, deviated 
in the direction of its rotation ; and therefore that end of the 
needle will still continue to deviate in the same direction ; 
that is, the direction of the rotation being the same in the 
two positions, the deviation by rotation will be in the same 
direction in both cases ; and consequently, between the two 
positions, either there is no position of the plane of the plate 
