of hot iron between the white and blood-red heat. 119 
find it stated in Newton's optics, that red hot iron has no mag- 
netic property; while Father Kircher asserts, that the mag- 
net will attract red hot iron as well as cold, (“ de Magnete” 
lib. 1). Again, in Vol. XVIII. No. 214. Phil. Trans, it is stated, 
that hot iron not only has an attraction for the magnet, but 
that its power is increased by the heat ; and these assertions 
have been repeated by many other authors, each supposing 
that his results were at variance with the other. 
M. Cavallo seems to have been the first writer, who was 
fully aware that these contradictory statements arose from 
the observations being made with the iron at different degrees 
of heat. He found, that although iron at the red heat had a 
greater power over the magnet than when cold, yet, at the 
white heat, it had a less ; but he says he is still unable to de- 
cide, whether all the magnetic power is intirely lost at the 
white heat. (Cavallo on Magnetism, p. 312.) More recent 
experiments on this subject are also recorded in Vol. IX. 
Part I. of the Transactions of the Royal Society of Edinburgh, 
by William Scoresby, Esq. But even here it does not ap- 
pear that this Gentleman was aware of the total loss of power 
at a certain temperature; for he observes, (after showing that 
iron red hot has a greater power than when cold) “ The 
contrary to this has, I think, been generally asserted from 
which it would seem, that he had not heated his iron to a 
sufficient degree to detect the non-action at the white heat. 
Notwithstanding therefore all the experiments that have 
been made, it is pretty evident from the above remarks, that 
considerable uncertainty still hangs over the results; arising, 
without doubt, from the want of proper conveniences for heat- 
ing bars of sufficient size, and to a proper degree of intensity, 
