iron arising from its rotation. ^6i 
from the centre of the needle was 13.2 inches; but as its 
edge was only 4*26 inches distant, the differences between 
the deviations corresponding to the several points on the 
plate were greatly increased ; and therefore, to obviate any 
inaccuracies that might arise, from the points not being 
brought into precisely the same situation when the plate 
revolved in the opposite directions, I increased the number 
of observations, making twenty-four for each position, 
namely, twelve points on the plate, as I have before de- 
scribed, the deviation for any point being observed when 
that point coincided with the line joining the centre of the 
plate and needle. The letters at the tops of the columns 
indicate the direction of rotation of the inner edge of the 
plate, or that nearest the centre of the needle. 
