312 Mr. Christie’s theory of the 
which I shall now describe, I made use of a flat ring of cast 
copper, the outer diameter of which is 11-9 inches, the inner 
diameter 10’05 inches, '24 inch in thickness, and weighing 
31 oz. Tr. In the interior side of this ring, three grooves 
were turned, and this side was covered with solder, consisting 
of 2 parts bismuth and 1 part lead, which, being fusible at a 
very low temperature, ensured a perfect contact between the 
copper ring and the bismuth which was cast in the interior of 
it. This formed a circular plate nearly 12 inches in diameter, 
and weighing 119 oz; Tr. A wooden axis passed through a 
hole, *3 inch in diameter, in the centre of the plate, so that 
it could be made to revolve in its own plane. 
This plate being placed vertically or horizontally, a small 
compass, with a needle two inches in length, very delicately 
supported, and having the rim within the box, which is of 
silver, accurately divided to degrees, was placed in different 
positions with regard to it ; the directive force of the needle 
being always diminished in the ratio of 9 to 1, by means of a 
bar magnet placed at an invariable distance to the south of 
the needle. Heat was then applied to a point in the periphery 
of the plate for a certain time, by means of a lamp with a 
small wick, giving a small and well defined flame. The 
lamp being removed, and the deviation of the needle observed, 
different points of the plate were successively brought under, 
or opposite to, the needle, according as it happened to be 
placed over, or by the side of, the plate, by turning it, in its 
own plane, about the axis at right angles to it, and the devia¬ 
tion of the needle corresponding to each position of the plate, 
noted. When the plate had been brought into its original 
position, and the deviation corresponding to this position 
