OP ARTS AND SCIENCES. 



197 



INVESTIGATIONS ON LIGHT AND HeaT, PUBUSHED WITH APPEOPRIATION FKOM THB 



RcMPORD Fund. 



XI. 



CONTRIBUTIONS FROM THE PHYSICAL LABORATORY OF 

 HARVARD UNIVERSITY. 



ON THE HEAT PRODUCED IN IRON AND STEEL 

 BY REVERSALS OF MAGNETIZATION. 



By John Trowbridge and Walter N. Hii.l. 



Presented May 29th, 1883. 



The object of our investigatioa was to determine whether the heat 

 which is generally attributed to rapid magnetizing and demagnetizing 

 is really due to this cause, or to induction currents in the mass of the 

 iron. Our work, however, had in the beginning a more practical object. 

 Since cylinders of iron and steel are heated when they are made the 

 cores of electro-magnets, and are submitted to the effects of rapidly 

 alternating currents, it was thought that they might exhibit different 

 decrrees of heating, and therefore that a process of determining the 

 character of iron and steel might be based upon the phenomena ob- 

 served, which could be called an electro-magnetic criterion of certain 

 physical properties of these metals. It is well known that chemical 

 analyses of steel and iron throw very little light upon their physical 

 properties, such as tenacity and elasticity in general. There is no sat- 

 isfactory test for the properties of different steels save by a testing- 

 machine, and this is not readily applicable in many cases. If a 

 method could be devised which depended simply upon electrical and 

 magnetic phenomena^ it would be a valuable aid to the metallurgist. 



The amount of sulphur, of phosphorus, and other ingredients be- 

 sides iron, is very small in steel, and it could hardly be expected that 

 their presence or absence could be detected by the difference of heat 

 developed under the influence of alternating currents, unless this heat- 

 ing is really due to molecular agitation produced by magnetization 

 and demagnetization. If the heating is due to alternating induction 

 currents in the mass of metal, there should be very little difference in 

 the amount of heat developed by different specimens of steel ; for their 

 electrical resistance would not differ sensibly from the presence or 

 absence of a fraction of one per cent of phosphorus or sulphur. If 

 the heating is due to magnetization or demagnetization, and to an 



a 



