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A Curious They mo -Magnetic Motor. 
21 ? 
II. A CURIOUS THERMO-MAGNETIC MOTOR. 
By Profs. Edwin J. Houston and Elihu Thomson. 
URING investigations by the authors, concerning the 
increase in the coercitive force of steel by changes 
of temperature, the following curious thermo-mag- 
netic motor was devised. This motor, though devoid of 
practical value, will, no doubt, be of sufficient scientific 
interest to warrant a short description : — 
In the figure, a disc or ring of thin steel, D, is mounted 
on an axis, so as to be quite free to move. The edges of the 
wheel are placed opposite the poles, h and s, of a magnet. 
In this position the wheel of course becomes magnetised by 
induction. 
If, now, any section of the wheel, as H, be sufficiently 
heated, the disk will move in the direction shown by the 
arrow. The cause of this motion is as follows : — The sec- 
tion H, when heated, has its coercitive force thereby 
increased, and being less powerfully magnetised by the in- 
duction of the pole s than the portion c, immediately 
adjacent to it, the attraction exerted by the pole s on the 
latter portion is thereby sufficient to cause a movement of 
the disk in the direction shown by the arrow. If a constant 
