OF FERRUGINOUS BODIES. 207 
in June the daily variation was a maximum, and 
that it again diminished with the recession of the 
sun till the latter part of December. 
5. From the data thus collected, Canton was 
led to infer that solar heat is probably the chief 
agent concerned in the production of the daily 
variation : and he devised avery ingenious expe- 
riment to illustrate his views, which, however, it 
failed to do strictly, for in that experiment he 
employed magnets uniformly heated, instead of 
imitating in them the unequal distribution of heat 
on the surface of the earth.* 
6. At a subsequent period Canton made an ex- 
tensive series of experiments on magnetic needles, 
by vibrating them at different degrees of tempe- 
rature, from which he found that an elevation of 
temperature invariably produced a diminution of 
power. 
* « Canton placed a compass-needle under the influence of 
two magnets, one on each side. When boiling water was 
poured on one magnet, the action of the other predominated 
on the compass-needle. He also exposed one of the magnets 
to the rays of the sun, whilst the other was screened, and 
found that the heated magnet lost a portion of its power.”— 
Phil. Trans. 
