KING. — MEASUREMENT OP THOMSON EFFECT IN COPPER, 379 



of the lines on the thermo-electric diagram given in J. J. Thomson's recent 

 book on electricity and magnetism, it is seen that the Thomson Effect 

 in iron should be about 5 times as great as in copper. Of course the 

 determination of relative values in this way depends on making Tait's 

 assumption that the Thomson Effect is directly proportional to the abso- 

 lute temperature. If this assumption be true the determination of the 

 Thomson Effect for different metals is very simple after its absolute value 

 for one has been found. In the experiments described above, copper 

 was chosen to be this particular one, because its properties suit the ex- 

 perimental conditions. As the results of the experiments are not in 

 accord with Tait's assumption, it would not be consistent to deduce values 

 of the Thomson Effect for other metals in the usual way. The further 

 investigation of these very fundamental points is very desirable. 



In closing, I wish to thank the authorities of the Jefferson Physical 

 Laboratory for their kindness, and especially Dr. Hall for his advice 

 and personal help with many difficult points. 



