the intensity of magnetic forces, ^c. 6 s 
is in direct contradiction to the notion which has been enter- 
tained of destroying the magnetism of the needle by the ap- 
plication of intense cold. 
2. With a certain increment of temperature, the decrement 
of intensity is not constant at all temperatures, but increases 
as the temperature increases. 
3. From a temperature of about 80° the intensity decreases 
very rapidly as the temperature increases : so that, if up to 
this temperature, the differences of the decrements are nearly 
constant, to ascertain which requires a precision in the expe- 
riments that perhaps their nature does not admit of, beyond 
this temperature, the differences of the decrem.ents also 
increase. 
4. Beyond the temperature of 100°, a portion of the power 
of the magnet is permanently destroyed. 
5. On a change of temperature, the most considerable 
portion of the effect, on the intensity of the magnet, is pro- 
duced instantaneously ; showing that the magnetic power 
resides on or very near the surface. This is more particu- 
larly observable when the temperature of the magnet is in- 
creased, little change of intensity taking place after the first 
effect is produced ; on the contrary, when the temperature 
of the magnet is diminished, although nearly the whole effect 
is produced instantly, yet the magnet appears to continue to 
gain a small power for some time. 
6 . The effects produced on unpolarized iron by changes of 
temperature are directly the reverse of those produced on a 
magnet ; an increase of temperature causing an increase in 
the magnetic power of the iron, the limits between which I 
observed being 50° and 100°. That the effect on iron of an 
