366 
iron arising from its rotation. 
from Q towards S, and those at o, o' to zero on the limb 
S<^N, as in Fig. 2. The deviations for the several points of 
the plate are those observed when these points coincided 
with the southern or upper part of the secondary to the 
equator and meridian ; and the direction of rotation is, as 
before, that of the edge of the plate nearest to the south pole 
of the sphere. 
II. Table of the deviations of a magnetic needle caused by the 
rotation of a circular plate of iron, when its centre was in the 
secondary to the equator and meridian, and its plane a tangent 
to the sphere : the distance as before 9.75 inches. Plate No. I. 
Points on 
the Plate. 
Long. 0°. 
Lat. 0°. 
Long. 180®. 
Lat. 0°. 
Long. 0°. 
Lat. 45® S. 
Long. 180°. 
Lat. 450 S. 
Long. o°. 
Lat. 45“ N. 
Long. 180°. 
Lat. 45° N. 
S to N 
N to S 
N toS 
S to N 
S toN 
N toS 
Nto S 
S to N 
StoN 
N to S 
N to S 
S to N 
0 
0 06 E 
fl / 
0 06E 
0 26W 
° / 
0 24W 
0 / 
7 24W 
Of 1 ° / 
7 22W6 48 E 
1 
0 / 
6 48 E 
0 1 
7 08 E 
0 , 
7 10 E 
lo . 
7 32 W 
0 , 
7 32 W 
90 
0 14 E 
0 14E 
0 40 W 
0 40W 
7 40 
i 00 
0 
6 56 
7 18 
7 20 
8 00 
7 58 
180 
0 04E 
0 04E 
0 32 W 
0 32W 
6 52 
6 54 
5 58 
6 00 
6 26 
6 26 j6 52 
6 52 
270 
0 04W 
0 04W 
0 20 W 
0 20W 
6 28 
6 28 
5 48 
5 48 
6 08 
6 08 j6 30 
6 28 
Mean 
Deviations 
0 5 E 
0 05 E 
0 29^ w 
0 2qW 
7 06W 
7 06W 
6 23 E*6 23 E 
1 
6 45 E 
6 46 e|7 13 ^ W 
7 
Deviation due 
to rotation 
0° 00' 
0° 00' 1 
0° 00' 
0® 00' 
0° 01' 
0® 01' 
From these observations, combined with the preceding, we 
may infer, that if the centre of the plate were made to de- 
scribe any parallel of latitude, the deviation due to rotation 
would be nothing when the longitude was 0° or 180°, and a 
maximum when the longitude was 90° or 270°, which is 
precisely the reverse of the absolute deviations that would be 
produced by the plate describing the parallel of latitude. 
