180 On the Magnetic Relations of the Metals. 
cerned in the argument above, are connected generally with 
the subject*. Wishing to know what relation that temperature 
which could take from a magnet its power over soft iron, had 
to that which could take from soft iron or steel its power rela- 
tive to a magnet, I gradually raised the temperature of a mag- 
net, and found that when scarcely at the boiling-point of al- 
mond oil it lost its polarity rather suddenly, and then acted 
with a magnet as cold soft iron: it required to be raised to a 
full orange heat before it lost its power as softiron. Hence 
the force of the steel to retain that condition of its particles 
which renders it a permanent magnet, gives way to heat at a 
far lower temperature than that which is necessary to prevent 
its particles assuming the same state by the inductive action of 
a neighbouring magnet. Hence at one temperature its par- 
ticles can of themselves retain a permanent state; whilst at a 
higher temperature that state, though it can be indeed from 
without, will continue only as long as “the inductive action lasts; 
and at a still higher temperature all capability of assuming 
this condition is lost. 
The temperature at which polarity was destroyed appeared 
to vary with the hardness and condition of the steel. 
Fragments of loadstone of very high power were then ex- 
perimented with. ‘These preserved their polarity at higher 
temperatures than the steel magnet; the heat of boiling oil was 
not sufficient to injure it. Just below visible ignition in thedark 
they lost their polarity, but from that to a temperature a little 
higher, being very dull ignition, they acted as soft ron would 
do, and then suddenly lost that power also. ‘Thus the load- 
stone retained its polarity longer than the steel magnet, but 
lost its capability of becoming a magnet by induction much 
sooner. When magnetic polarity was given to it by contact 
with amagnet, it retained this power up to the same degree 
of temperature as that at which it held its first and natural 
magnetism. 
A very ingenious magnetizing process, in which electro-mag- 
mets and a ‘high temperature are used, has been proposed 
lately by M. Aimé+. Iam not acquainted with the actual 
results of this process, but it would appear probable that the 
temperature which decides the existence of the polarity, and 
above which all seems at liberty in the bar, is that required. 
Hence probably it will be found that a white heat is not more 
advantageous in the process than a temperature just above or 
about that of boiling oil; whilst the latter would be much 
* See on this subject, Christie on Effects of Temperature, &c. Phil. 
Trans. 1825, p. 62, &c. 
+ Annales de Chimie et de Physique, tome lvii. p. 442. 
