114 PKOCEEDINGS OP THE AMERICAN ACADEMY 



Investigations on Light and Heat, made and published wholly or in part with 

 appropriation from the Rumfokd Fund. 



VIII. 



ON THE HEAT PRODUCED BY THE RAPID MAGNETI- 

 ZATION AND DEMAGNETIZATION OF THE 

 MAGNETIC METALS. 



By Joh*n Trowbridge, S.D., 



Harvard University. 



AND 



Walter N. Hill, S.B., Harvard University, 



U. S. Torpedo Station, Newport, R.I. 

 Presented, Dec. 11, 1878. 



The fact that iron and steel become heated when rapidly magnetized 

 and demagnetized, has long been known. It is, perhaps, one of the 

 most significant facts in the subject of magnetism ; for it is an out- 

 ward manifestation of the inner work that is done among the mole- 

 cules when they are endowed and then suddenly deprived of the state 

 which we call magnetism. It gives color to the theory that each par- 

 ticle of iron is given a polarity, and also is twisted or strained in its 

 bed, or caused to vibrate ; and brings the subject of the magnetic state 

 of metals into the domain of mechanics, instead of relegating it to the 

 theory of fluids. "When we magnetize a bar of steel, the magnet with 

 which we magnetize is not sensibly altered, — it has the same strength 

 as before, — while the piece of steel has been endowed with a new 

 property. How is the doctrine of the conservation of force satisfied ? 

 The resulting magnetic state in the piece of steel is not the equivalent 

 of the mechanical motion which the hand gives to the stroking mag- 

 net ; for it is not necessary to move the magnet. The piece of steel 

 can be left in contact with the poles of the magnetizing magnet. "We 

 are forced to conclude that the particles of the steel have been forced 

 into a state of strain, in which the mechanical properties, such as elas- 

 ticity and viscosity, are involved ; and, when we deprive a piece of steel 

 of this mechanical condition, we heat it, just as we can heat a rod of 

 glass or of steel, by stroking it with a cloth covered with resin, and 

 thereby setting it into longitudinal vibration. The rod of glass or steel 

 gives forth a musical note when thus set into longitudinal vibration. 



