Chemistry and Physics. 59 
‘the heat developed by magnetizing and demagnetizing is due to 
molecular heating. If it is due entirely to induction currents in 
the metals, the slight changes in electrical resistance produced by 
small quantities of sulphur, of phosphorus, and of carbon would 
be inappreciable in the masses of iron which we used, and we 
should expect to obtain under the same conditions the same rise 
in temperature for the different specimens of steel. Our previous 
work* on cobalt and nickel must therefore have been affected by 
some error, 
We next determined to ascertain if the heating was confined to 
the surface of the metallic cores. Theory indicates this to be the 
ably entirely due to conduction of heat, as can be seen by com- 
communicate vibrations to a solid bar of iron one inch and a half 
in diameter. If the bar vibrates as a whole, a certain amount of 
heating of the bar takes place throughout its interior. The heat 
in the interior of the bar, however, must. be less than that at the 
‘“xterlor, where the magnetization exists in full strength. e 
coil 
magnetic attractions; for the note can be heard when the iron 
an alternating current, shows very strikingly the fact that it takes 
me to magnetize, and that magnetism resides upon the exterior 
electro-magnets. Under the influence of strong currents 
* Proceedings of the American Academy, 1878-79, p. 114. 
