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



under an alternating magnetic field the magnetic critical 

 temperature would be 50° or more lower, but the sharp 

 change of electrical resistance in the neighbourhood of 400° 

 remains the same with or without an alternating field. Now, 

 if under an alternating field an intrinsic field of 10 7 gausses 

 is suppressed at the lower temperature of about 350° C, 

 then the resistivity of the nickel ought to have been altered 

 in two ways : first, from the fact that a field of 10 4 gausses 

 causes a change of about 2 per cent, in the resistivity, a 

 change of field of 10 7 gausses ought to have produced an 

 appreciable effect ; and secondly, the sharp bend in the 

 curve, where the temperature coefficient of resistance passes 

 to a normal value, ought to have suffered some displacement 

 towards the new critical temperature. As neither of these 

 anticipated results is realized, these experiments do not 

 support the hypothesis of an intrinsic magnetic field of 

 enormous magnitude. 



3. Thermo-Electric Power. — The thermo-electric powder of 

 both nickel and iron changes as the critical temperature is 

 approached in a very striking way, the straight lines con- 

 necting thermo-electric power and temperature curving 

 round through rather more than a right angle, and then, 

 at the critical temperature, bending very sharply back again 

 so as to become roughly parallel to the original direction 

 as seen in fig. 4. If this bending of the thermo-electric 

 lines is due to the gradual diminution and finally sudden loss 

 of an immense intrinsic magnetic field, then a lowering- of 

 the critical temperature ought to be in evidence in the cur- 

 vature of the thermo-electric lines. 



A thermo-junction of nickel-platinum was placed side 

 by side with a standard junction of platinum-iridium and 

 platinum in an electric heater inside of which an alternating 

 field of 100 gausses could be maintained. It was then an 

 easy matter to compare accurately the readings of the two 

 junctions with and without an alternating field. A previous 

 experiment showed that the standard junction was uninflu- 

 enced by a magnetic field of 100 gausses. The scale readings 

 allowed a potential difference down to 25 micro-volts to be 

 observed, and a temperature of 1° C. to be estimated. 

 Readings taken both up and down the scale were exactly 

 alike whether the thermo-junction s were acted upon or not 

 by an alternating field. A similar experiment carried out 

 with an iron-platinum thermo-junction also showed that there 

 was no difference whether the junction was under the action 

 of an alternating field or not. Thus, again, while the critical 



