19^ Lieut. Foster’s account of the 
On looking over the several columns of the preceding 
Table, it will be seen that the zeros for the same point 
changed according as the points on the plate were made to 
coincide with the fixed mark or index in the order of o, 60, 
120, 180, &c. or in the order of o, 300, 240, 180, &c. and 
also, that when they were applied in the order of o, 60, 120, 
180, & c. the easterly deviation produced by the rotation of the 
plate from east to west, was greater than the westerly devia- 
tion caused by its rotation from west to east ; and that precisely 
the reverse took place when the points of the plate were ap- 
plied in the order of 300, 240, 180, &c. From the manner 
in which the deviations due to the rotation of the plate were 
obtained, for each order of succession of the points, marked 
on its surface; it is obvious that the plate made two complete 
revolutions during the series ; the first in the direction from 
west to east, in consequence of the manner in which the 
points were numbered on the plate, and the second from 
east to west ; to which circumstance is attributed the change 
that is observed in the zeros, or readings before rotation, as 
well as, that the amount of the deviations, due to rotation 
from east to west, and from west to east, change in their 
respective columns. 
Observations similar to those in Table I. were made when 
the centre of the plate was in the several situations indicated 
in Tables II. and IV. ; but as it was considered that giving 
them in detail would unnecessarily extend this communica- 
tion, the mean results have been collected in these Tables, 
and the observations at length deposited with the Royal 
Society, in order that they may-be consulted should any of 
the results appear of sufficient interest to require minute 
investigation at a future time. 
