180 DR. FARADAY’S EXPERLMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXX.) 
the range employed, i. e. from 0° to 300°, the three metals seem to be in different parts 
of their course ; nickel has passed the period of its maximum force, iron is in it, and 
cobalt has not yet attained to it ; and this accords with the further change by tem- 
perature ; for by greater elevation nickel first loses its distinctive power at about 
635°Fahr.*; then iron at a moderate red heat'f', and cobalt at a far higher tempe- 
rature than either, near the melting-point of copper. Such a view as this increases 
very much the interest of the relation between heat and magnetism ; especially as, if 
it be well founded, it v/ill probably apply to substances in all states; to gases as 
oxygen as well as to metals like cobalt ; in which case it may be that all bodies, 
whether paramagnetic or diamagnetic, have a certain temperature at winch their 
induced magnetic condition being most favoured is a maximum, and above or below 
which tlseir state diminishes. 
3429. The effect of heat upon iron and steel, and therefore upon magnets generally, 
will have hereafter to be distinguished into that which it may produce in the case of 
iron considered as perfectly soft; and that which it may produce in the case of per- 
fectly hard steel whether charged magnetically or not. It may be that its action upon 
a magnet, consisting of parts all equally hard and equally charged, may be very dif- 
ferent from its action upon another magnet, having superficial or terminal parts 
harder and more charged than the rest ; or as is usually the case, of which the parts 
are not, as steel, exactly alike, but give a resultant of many different actions 
3430. In considering these remarkable effects of heat, the question still recurs, can 
substances be made to pass each other magnetically by any change of temperature? 
ft does not appear as yet that any of them, being unmixed, can pass the zero pre- 
sented by a vacuum or carbonic acid gas, i. e. none can be converted from the para- 
magnetic to the diamagnetic state, or vice versa, these states being defined by that 
zero ; and so far that would appear to be a true and natural zero. The further 
question may be asked, whether, if equal volumes of different bodies in the same 
shape were subjected to an equal magnetic force, at various temperatures, so that 
their forces might be expressed in their full and true relation, upon one diagram 
scale, would the lines expressing these forces ever cross each other? as far as I can 
see they would not ; but the results are as yet far too few in number, and too imper- 
fect in their nature, to justify any serious conclusion. 
* Experimental Researches, 8vo, vol. ii. p. 219. t Ibid, vol, iii. p. 444. 
Royal Institution, October 9th, 1855. 
