292 
Mr Christie’s Observations 
Angle 
from 
the 
Meri- 
dian. 
Distance 
of needle 
from centre 
of table. 
Calculated 
height at 
which de- 
viation 
should —0. 
Observed 
height at 
which de- 
viation =0. 
Difference be- 
tween the ob- 
served and 
calculated 
heights. 
r 
14 
3.797 
3.75 
— .047 
tf* 
o 
o 
16 
4.340 
4.33 
= .010 
i 
IB 
4.882 
4.90 
+ .018 
[ 
14 
3.187 
3.20 
+ .013 
60° - 
16 
3.642 
3.70 
+ .058 
18 
4.097 
4.15 
+ .053 
In the observations made from the south towards the east , 
the deviations of the north end of the needle were first easterly , 
that is from the ball, in which direction they gradually increased 
as the ball descended, and attained a maximum ; they then de- 
creased to zero, became westerly, attained a maximum in this 
direction, and then decreased until the needle resumed its ori- 
ginal position. In the observations made from the north to- 
wards the west, the deviations were exactly in a contrary order. 
All these were precisely what I had anticipated. 
Having ascertained that the quality of the deviations was 
such as would be the necessary consequence of my hypothesis, 
my next object was to discover whether their quantity was such 
as would fully confirm this hypothesis, or was altogether incom- 
patible with it. As the precise deviation of the horizontal 
needle must depend on the law according to which the magne- 
tic particles in the line sCn were affected by the ball, and on 
the manner in which these particles acted on the poles of the 
needle ; and as I found there must necessarily, in the first in- 
stance, be almost insuperable difficulties in the determination of 
these laws, I endeavoured to find some further criterion of the 
correctness of the hypothesis, that should be independent of the 
nature of these laws. 
If the ball acted alone on the particles in the line sC n, it was 
evident that being carried round that line, so that its perpendi- 
cular distance from any one point in it should always be the 
same, then these particles must always be influenced in the same 
manner towards the ball ; and, consequently, a needle, in the si- 
