320 
Mr. Christie’s theory of the 
as the plate turned on its axis, passing to the south of the needle 
and repelling its sotith end, or north pole. When the needle was 
to the south of the plate, similar changes in its direction fix the 
position of a south pole in a point on its south, or unmarked sur¬ 
face opposite to the north pole on the north side. The obser¬ 
vations below the centre indicate the same positions for the 
pole. I should mention that these observations were made when 
o was the heated point: but to leave no doubt with regard to 
these results being due to a uniform action in the plate, I 
made corresponding observations when 315, 270, 225, 180, 
135, 90, 45 were successively the heated points, and in all 
cases obtained corresponding results. By reversing the sides 
of the plate, that is, making the marked face south, the obser¬ 
vations showed that the positions of the poles were indepen¬ 
dent of this circumstance. 
From the deviations being of the same character, but of 
greater extent, when the needle was opposite to the line of 
junction of the copper and bismuth than when opposite to 
the outer edge of the copper, it would follow, that the poles 
were nearer to the centre of the plate than this line of junction. 
I afterwards found, by placing the compass in the horizontal 
plane passing through the centre of the plate, and at different 
distances from it towards the east, that when the place of 
heat was the lowest point, the north pole on the north side of 
the plate was in the vertical 4 inches to the east of the centre, 
and helow the compass ; and when the centre of the needle was 
at this distance to the east, by making the place of heat describe 
45° towards the compass, the north pole appeared to be a little to 
the east of the needle’s centre, and above it. I thus determined, 
pretty accurately, that the lines drawn to the poles on the 
east side of the axis of heat, made an angle with that axis of 
