the Intrinsic Field of a Magnet. 407 



temperature for magnetism may be lowered by an alternating 

 field, no corresponding change in the disposition of the 

 sharply curved part of the thermo-electric lines is dis- 

 cernible, and again there is no evidence in support of the 

 hypothesis of an intrinsic magnetic field of enormous mag- 

 nitude. 



4. Specific Heat. — The specific heat of the f'erro-magnetic 

 metals is not constant, but increases at first slowly and later 

 more rapidly as the critical temperature is approached, and 

 at this temperature falls almost abruptly to a lower value. 

 Weiss * considers this change of specific heat to be due to • 

 the gradual loss and final destruction of the intrinsic mag- 

 netic field of 10' gausses, and shows that the thermal energy 

 which has to be supplied, due to such an increase of specific 

 heat, is almost exactly equal to the energy required to 

 destroy a field of this magnitude |. If the intrinsic magnetic 

 field is so large as 10 7 gausses, the abrupt drop in the 

 enhanced specific heat ought to take place at a lower tem- 

 perature when the critical temperature for magnetism is ' 

 lowered by an alternating field. Experiments on nickel and 

 iron were made with great care to ascertain if this were the 

 fact. 



The nickel experiments were made in three ways. First, 

 a nickel wire 0°088 cm. in diameter, wound into a close short 

 spiral, was fixed in a vertical position with a thermo-junction 

 inside it and very nearly in contact with it. This was sur- 

 rounded with a porcelain tube closed at the top which served 

 as a "jacket " to protect the spiral from draughts of air, and 

 by means of a high resistance wire embedded in the porcelain 

 tube through which a current of electricity could be run, 

 the temperature inside the tube could be suitably regulated. 

 Arrangements were made to heat the nickel by passing a 

 continuous or alternating current through it, and this set up 

 a steady or alternating field as might be ieqnired. The 

 change of specific heat was traced by observing the rate of 

 cooling from a temperature a little higher to a temperature 

 a little lower than the critical temperature, and confirmatory 

 experiments were made by observing the rate of heating 

 through a similar interval of temperature. The electrical 

 arrangements for heating the wire and regulating the sur- 



* Weiss & Beck, Journal cle Physique, ser. 4, vol. vii. p. 249. 



T This result, however, is not a sound argument in favour of a mag- 

 netic field of 10 7 gausses, inasmuch as the constant of the intrinsic field is 

 derived from considerations of thermal energy. 



