1904.] Thermoelectric Power produced by Magnetisation. 429 



A glance at any of the curves of thermoelectric force for iron will 

 show how easily errors might arise if it were assumed that a wire which 

 had been subjected to a magnetic field became perfectly demagnetised 

 when the field was withdrawn. In all my experiments the curves 

 would have been much lower but for the demagnetisation by reversals 

 before every observation. The dimensional ratio of the short wires 

 which I used was generally so small, and the self -demagnetising 

 consequently so great, that an apparent reversal of thermoelectric force 

 in strong fields did not often occur. But in the case of a wire 17*5 cm. 

 in length and 0*026 cm. in diameter, this spurious reversal appeared in 

 fields above 500. When the demagnetised wire was subjected to a 

 field exceeding this strength, there occurred a galvanometer deflection 

 to the right, indicating a genuine increase of thermoelectric force ; but 

 when the magnetising current was interrupted, the spot of light, instead 

 of going back again, went still further to the right, the thermoelectric 

 force due to the residual magnetism being greater than that due to the 

 strong field. When the magnetising circuit was again closed before the 

 wire was demagnetised, the spot of light, of course, moved to the left, 

 and if the residual magnetism were disregarded, it would naturally be 

 supposed that a reversal of thermoelectric force was indicated. The 

 spurious reversal was also very conspicuous in the case of the steel 

 wires. 



VOL. LXXIII. 2 H 



