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XXIX. The Thermal Effect due to Reversals of Magnetization 



in Soft Iron. By A. Tanakadate, Rigakusi*. 



[Plates VI.-VIIL] 



THE following experiment on the measurement of the heat 

 due to the reversals of magnetization in soft iron wire 

 was carried out in the Physical Laboratory of the Glasgow 

 University during the summer months of 1888. The method 

 pursued is due to Sir William Thomson, in accordance with 

 whose instructions the work was undertaken. 



Cotton-covered soft iron wire, of "115 centim. diameter, was 

 coiled upon a specially prepared wooden groove. The ends of 

 the wire were insulated from each other ; and the bundle was 

 tied at several places with fine silk thread to keep its shape, 

 and when the wooden frame was removed the coil of the 

 wire was left in shape of an anchor-ring. The object of thus 

 building the ring with insulated wire instead of solid mass 

 was to reduce the Foucault current in the substance of iron 

 when an alternating current is passed in the magnetizing coil. 



The ring thus formed w T as now wound uniformly over with 

 No. 16 silk-covered copper wire in two layers, a thermoelec- 

 tric junction consisting of platinoid and copper being placed 

 upon the outer surface of the ring before winding. The 

 principal dimensions of the ring were as follows : — 



Diameter of the soft iron wire . . . . 0*115 centim. 



Number of turns of the soft iron wire in 

 the ring 130 



Total number of turns of copper wire in 

 the magnetizing solenoid 177 



Internal diameter of the ring 6 centim. 



External diameter of the ring 10 „ 



Mean 8 „ 



Mean strength of magnetizing field due to 1 ampere through 

 the coil 1 77 



=^ / n 1A =8-85C.G.S. 



87TX 10 



A wooden ring, of very nearly the same size and shape as 

 that of the iron wire, was turned and wound similarly with 

 the same silk-covered copper wire, total number of turns, 

 however, being 174. The other junction of the same thermo- 

 electric couple was laid on the surface of this wooden ring in 

 the same way as the other junction was disposed with regard 

 to the iron ring, so that the platinoid wire stretched between 

 the two rings, and copper wire from the two rings led to 

 terminals of a mirror-galvanometer, as in the diagram. 



The magnetizing coils of the two rings were joined in series, 

 * Conmiunicated by Sir William Thomson. 



