iron arising from the rotation 38 1 
place ; it, however, led me to ascertain precisely the point at 
which the deviation due to rotation vanishes 
VII. Table of the deviations of a magnetic needle caused by the rotation 
of a circular ylate of iron when the centre and plane of the plate were 
in the secondary to the meridian and equator, and its centre in latitude 
54 “ 45 '. 
Lat. 54° 
45 ' S' 
Lat. 54® 
45* N. 
Long. 
180°. 
Long. 0° 
Long. 
180®. 
Long. 0®. 
Upper Edge. 
E to W 
Wto E 
W to E 
E to W 
W to E 
E to W 
E to W 
W to E 
0 
30 
60 
90 
120 
150 
180 
210 
240 
270 
300 
330 
0 / 
20 42 E 
20 30 
19 54 
19 18 
19 50 
19 38 
20 16 
21 30 
22 32 
22 26 
22 02 
21 26 
0 / 
20 42 E 
20 32 
19 56 
19 20 
19 52 
^9 38 
20 16 
21 26 
22 32 
22 28 
22 04 
2l 26 
0 / 
20 44W 
19 so 
19 30 
20 26 
20 50 
21 42 
22 22 
22 22 
21 34 
20 42 
20 30 
20 36 
0 / 
20 44W 
19 50 
19 28 
20 24 
20 46 
21 46 
22 24 
22 20 
21 34 
20 42 
20 30 
j 20 36 
21 36W 
21 10 
20 50 
20 16 
20 24 
19 52 
19 46 
19 24 
19 28 
20 28 
21 10 
21 12 
0 / 
21 40 W 
21 10 
20 50 
20 18 
20 22 
19 50 
19 44 
19 20 
19 28 
20 30 
21 lO 
21 18 
0 / 
19 56E 
20 18 
20 44 
20 56 
20 48 
20 34 
19 50 
19 40 
19 09 
19 58 
19 38 
20 00 
0 / 
19 56E 
20 20 
20 44 
20 58 
20 50 
20 36 
19 so 
19 40 
19 08 
19 00 
19 38 
20 02 
Mean 
Deviations. 
20 50^ 
20 51 
20 55 1 
20 ssi 
1 
20 28 
20 28 ^ 
20 02 1 
20 03 J 
Deviation due 
to rotation. 
— 0° oo|' 
4- 0° 00'-^ 
ooy 
— 0 
3 01' 
General law of the deviation due to rotation deduced from the 
experiments. 
Having now ascertained the nature of the effects produced 
on the horizontal needle by the rotation of the plate in diffe- 
rent planes, I endeavoured to discover some general law, ac- 
cording to which the direction of the deviation depended on 
the direction of the rotation of the plate ; so that the situation 
of the centre of the plate, the plane in which it revolved, and 
