repetition of Mr. Christie's experiments , &c. 191 
was again fixed in its proper position, with its point 60 coin- 
ciding with the index, and the deviation caused by rotation 
obtained in the same way, and in like manner for the rest of 
the points 120, 180, 240, 300, o, in their order, and likewise 
in the order of succession 300, 240, 180, 120, 60, o. 
The various effects due to the rotation of he plate, when 
placed in the different magnetic positions above specified, are 
noted in the tabulated experiments at each : it may never- 
theless be proper here to state the nature of these deviations, 
in the different adjustments of the plate to the compass ; as 
for instance, in the experiments with its plane in the plane 
of the secondary, placed at Sand N, fig. 4, 16,4 inches from 
the centre of the needle, the deviations were invariably to 
the east ; when its upper edge was made to revolve from 
west to east, and to the west in the opposite rotation : at the 
points e and w effects just the contrary were produced, viz. that 
while the upper edge of the plate revolved from west to east, 
the deflections were to the west, and in the opposite rotation to 
the east ; from which circumstance it was inferred, that there 
must be an intermediate latitude where no deviations of the 
needle would be produced by rotation, and this by experi- 
ment was ascertained to be latitude 52°^ North and south, as 
stated in the observations. The effects of rotation of the 
plate on the needle when placed with its plane a tangent to 
the sphere, at the points E and Q, fig. 3, were considerable, 
and always to the west, the upper edge revolving from east 
to west ; but at the other positions N Sf and w, no effect due 
to rotation was observable. The maximum effect of rotation 
(amounting to 108° in one instance) was produced with the 
plate in lat. 52°^ N, long. 270°, thirteen inches from the 
