390 Mr. Christie on the magnetism of 
From these observations it appears that, the plane of the 
plate being in the plane of vibration of the needle, and its 
centre in the equator, the deviation of the upper or south end 
of the needle, due to rotation, was in the direction of the rota- 
tion of the upper or south edge of the plate, and of the north 
end in that of the north edge ; and we may therefore conclude, 
that if a needle could be freely suspended by its centre of 
gravity, and the centre of the plate were in the equator, and 
its plane in that of the secondary to the meridian and equa- 
tor, the deviation of the south end, due to rotation, would be in 
the direction in which the south edge of the plate revolved, 
and of the north end, in that in which the north edge revolved ; 
w’l ch, again are precisely the directions in which we have 
seen, that the horizontal needle deviated by the rotation of 
the plate in this position. 
X. Table of the inclinations of the dipping needle, ichen the centre of the plate 
was in latitude 90° South, and its plane in the plane of the meridian, or plane 
of vibration of the dipping needle ; the distance of the centre of the plate from 
that of the needle being 13.3 inches. • Plate No. I. 
Points on the 
Plate coincid 
ing with the 
Pmar South. 
Polar South edge of the Plate to Equatorial North, 
or 
Equatorial South edge to Polar South. 
Polar South edge of the Plate to Equatorial South, 
or 
Equatorial South edge to Polar North. 
First Set. 
Second Set. 
First Set. 
Second Set. 
S. end. 
N. end. 
S. end. 
N. end. 
S. end. 
N. end. 
S. end. 
N. end. 
0 
60 
120 
180 
240 
300 
0 ' 
71 05 
71 00 
71 lO 
71 40 
71 40 
71 05 
0 / 
71 05 
71 10 
71 15 
7 * 45 
7 « 45 
71 10 
0 / 
71 35 
71 10 
71 25 
7 * 35 
71 30 
71 25 
0 , 
71 30 
71 05 
71 25 
71 40 
71 35 
71 35 
0 / 
71 40 
71 35 
71 40 
72 00 
72 05 
71 40 
0 / 
71 40 
71 15 
71 30 
71 50 
72 05 
7 » 55 
0 / 
71 50 
7 « 35 
72 15 
72 30 
72 15 
72 00 
0 / 
71 40 
71 25 
72 05 
72 20 
72 05 
7 * 55 
Mean dip. 71° 23' 
M 1 0 r <7 ^ 1 
71 52-11- 
Mean deviation due to rotation. o° 29' 
• In these observations the edge of the iron plate was not an inch from the south end of the 
needle; so that a very small error in the position of the plate’s centre will account for the dip in 
both directions of rotation being grtatcr than 70° 15', the true dip. 
