88 A, M. Mayer—LEffects of Magnetization 
ed 
In a paper “ On the Calorific Effects of Magneto-Electricity, and 
Pp tr gn P : 
oule to the first experimental determination ever made of 
“the mechanical value of heat.” 
t may be of interest to present the following account of the 
experiments made by Van Breda and Grove, taken from 
aguin’s Traité de Physique, 1861, vol. III, p. 621. “M. Van 
Breda having enveloped a tube of iron with a helix through 
which he passed an intermittent current, found a heating of 
the iron due to the alternative displacement of the molecules,* 
the heat being shown by the dilatation of the air contained 
in the tube, which formed. a reservoir of an air thermometer. 
gave similar results, but less marked; while non-magnetic 
metals were not heated in the same circumstances. I have 
made many experiments on a tube of iron, weighing two hun- 
dred weight, which confirm these results. The experiments will 
be given in Part III. of this memoir. 
here present two tables of experiments on rod No. 2, of 
Ulster iron, The successive discussion of these two tables will 
give to the reader a clear physical conception of the phenomena, 
and serve to elucidate the account I have above given of the 
heat developed on demagnetization. 
* The heat observed, however, may not be entirely due to these motions, for the 
thermal effects may in part be due to the currents induced in the iron on magnet- 
ization and demagnetization. 
