404 Dr. J. R. Ashworth on the Theory of 



lower temperature, instead of the normal critical temperature* 

 when an alternating field is applied. The three properties 

 refer red to — electrical resistivity, thermo-electric power, and 

 specific heat, which all exhibit abnormal effects up to the 

 magnetic critical temperature, — have been selected for inves- 

 tigation to see if any change occurs under an alternating 

 field at the lowered critical temperature, and in this way to 

 decide if the intrinsic magnetic field has a magnitude large 

 enough to influence these properties. 



2. Electrical Resistivity. — A length of nickel wire 0'088 

 cm. in diameter was folded buck and forward on itself in 

 six parallel lengths, the ends being joined to stout copper 

 wires which made connexion with the testing apparatus. 

 The nickel wire was placed in a heating tube made of 

 porcelain in which was embedded a spiral of high-resistance 

 wire through which a current of electricity could be passed 

 to generate the requisite temperature. This tube and its 

 contents were put inside a large solenoid of 525 turns of 

 wire, wound in a space of 21*4 cms., through which an 

 alternating current was made to flow, when required, for the 

 purpose of submitting the nickel wire to an alternating field ; 

 arrangements were also made so that the alternating field 

 could be applied transversely to the nickel, since the resist- 

 ivity of nickel is known to change, although to a very small 

 extent, in opposite ways under longitudinal and transverse 

 magnetic fields of great strength. In these experiments the 

 field used was not, however, carried beyond 100 gausses,. 

 and the full strength of this field only produced a change of 

 resistance of about one-thousandth of an ohm, a practically 

 negligible quantity. The resistance was measured by a fall 

 of potential method in one set of experiments, and by a 

 Wheatstone bridge method in another set, and the tempe- 

 rature was determined by means of a thermo- junction. 

 Readings of temperature and resistance for very slow heat- 

 ings and coolings were made with and without an alternating 

 magnetic field in successive experiments, and the field was 

 in one set longitudinal, and in another transverse, to the 

 length of the nickel wire, and in a third set a circular field 

 was applied by running an alternating current through the 

 wire, but in no case was there any perceptible difference in 

 the electrical resistance whether the alternating field was on 

 or off. 



Table L, and the curve in fig. 2 constructed from it, is an 

 example of what takes place in general. The critical tempe- 

 rature for this sample of nickel is a little above 400° C, and, 



