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BRUSH— SPONTANEOUS GENERATION OF HEAT [April 22, 



spherical end which accurately seats itself in a hollow metal cone. 

 The rods are quickly removable through vertical slots in the cones. 

 After some preliminary experiments, to get acquainted with the 

 apparatus, a fresh rod H was hardened by placing it horizontally in 

 a wooden rack just above a trough of water at room temperature,' 

 quickly heating it to bright redness by passing suitable electric 



Fig. 4. 



current through it and plunging it in the water beneath, the act of 

 lowering the rod serving to break the electric circuit. The rod 

 was kept straight while hot by means of a weak spiral spring which 

 took up the expansion. Preliminary experiments had shoAvn that a 

 rod could be hardened in this way without warping. 



The hardened rod, already at room temperature, was quickly 

 wiped dry and put in place beside G. Then, without delay, a fine 



