OF FERRUGINOUS BODIES. 919 
afterwards learned from Brewster’s Treatise on 
Magnetism, had heated the extremities of a bar 
magnet, and thus shifted its poles. My experi- 
ments, however, were conducted differently from 
those of Kuppfer, and led to other results than 
those which the Russian philosopher had disco- 
vered. They form the substance of my third 
memoir, also read before the London Electrical 
Society, in the same year.* 
16. In that memoir I showed that the action 
of caloric on the poles of a magnet is subject to a 
general law, which, as regards their transplace- 
ment, longitudinally, or along the magnetic axis, 
is from the point of heat. In accordance with 
this law, the magnetic poles may be shifted 
either in the same direction, or in opposite direc- 
tions; and the magnetic axis joining those poles, 
may be either elongated, or contracted, at plea- 
sure, according to the situation of the point of 
heat. 
17. Lalso discovered that, after a few repeti- 
tions of an elevation of temperature, (by means 
of a spirit lamp only) the transplacement of the 
magnetic poles becomes lessened: and, even- 
* Annals of Electricity, &c., vol. iv. 
