323 
diurnal variation of the magnetic needle , & c. 
In this position of the plate, the deviations of the needle 
arising from the action of four poles in the plate, in the situ- 
ations I have indicated, with the compass in corresponding 
positions on contrary sides of the plate, would, in each, be 
in the same direction, the preponderating force on the one 
side being attractive, on the other side repulsive. These 
deviations would not however be equal ; the limit of the de- 
viation due to the attractive force, however great, being the 
azimuth of the attracting pole from the centre of the com- 
pass ; and the limit of that due to the repulsive, the supple- 
ment of this angle. So that when the force is considerable, 
and this angle much less than a right angle, the deviation 
arising from the repulsive force on one side, will greatly 
exceed that due to an equal attractive force on the other. 
On examining the deviations in these tables, it will be found, 
that, when the deviation on one side of the plate greatly 
exceeds the corresponding one on the other, as 77 0 W., 
38° 45' W. ; 74° W., 29 0 W. ; 65° 30' E., 30° 15' E. ; 72 0 E., 
38° 30' E. ; See., the situations of the poles were such that 
the deviations in the former cases were due to repulsion, and 
in the latter to attraction. 
The deviations corresponding to the angular distance o, 
being in this position of the plate all easterly, is in accord- 
ance with what I have stated with regard to the inclination 
of the axis of polarity to the axis of heat. According to this, 
was applied, the deviation was N. 140° E„ and when it was removed, the needle 
stood for an instant at N. 117 0 E., and then moved gradually back till it came to 
N. io° E., when the observation was made. This great deviation, probably, arose 
from some irregularity in the action of the flame during the time it was applied ; 
or, possibly, of the plate itself, rendered, in this position of the compass, at that 
time particularly sensible. 
