142 Mr Christie on the Effects of Temperature 
paper ; and then, describing the compass and magnets made 
use of (the verbal description being illustrated by an engra- 
ving), he gives the subjoined account of the mode of experi- 
menting adopted. 
<c A meridian line being drawn on a firm tabic, standing on a 
stone floor, the compass was accurately adjusted on it, so that 
the needle pointed to zero on the graduated circle. The mag- 
nets were fixed at the bottoms of earthen pans, secured in such 
a way to rectangular pieces of board that their positions could 
not be accidentally changed, and projecting from these boards 
were small pieces of brass, on each of which a line was drawn, to 
indicate the position of the axis of the magnet ; the horizontal 
distance of the edge of each of the projections nearest to the 
needle from the corresponding end of the magnet within the 
pan, was exactly three inches ; I could, therefore, in any in- 
stance, determine very accurately the distance of the centre 
of the magnet from that of the needle. The pans were placed 
on the table, so that the indexes on the pieces of brass coin- 
cided with the meridian line. Water was now poured into 
the pans, and the temperature of the magnets was varied by va- 
rying the temperature of the water. The temperature of each 
magnet was ascertained by a thermometer placed in the water, 
with its bulb resting on that pole of the magnet which was near- 
est to the centre of the needle. In my first observations I, 
however, made use of only one thermometer, which was moved 
during them from one magnet to the other.” 
“ The observations contained in the tables were made thus : 
I first noted the time, and then the temperature of the north 
magnet ; after which I placed the thermometer on the pole of 
the south magnet. I next observed the westerly point, at 
which the needle was held in cequilibrio by the terrestrial 
forces and those of the magnets, slightly agitating the needle, 
that it might the more readily assume the true position ; from 
this it was led, by means of a very small and weak magnet, 
held on the outside of the compass-box, towards the easterly 
point of equilibrium, which was observed in the same manner ; 
and from this it was led in the same way towards the souther- 
ly point. After these observations of the points of equilibri- 
um, the temperature of the south magnet being observed, the 
2 
