GUSTAV MAGNUS. 23 



had been softened by heat; or those in which the 

 parts in contact had very different temperatures. He 

 was convinced that the thermo-electrical current was 

 due neither to the radiating power, nor to the conduc- 

 tivity for heat, using this expression in its ordinary 

 meaning, and he had to content himself with the ob- 

 viously imperfect explanation that two pieces of the 

 same metal at different temperatures acted like dis- 

 similar conductors, which like liquids do not fall in with 

 the potential series. The solution was first furnished 

 by the two general laws of the mechanical theory of heat. 

 Magnus's hope was not unfulfilled. Sir W. Thomson 

 discovered that alterations in the conductivity for heat, 

 though such as were produced by the electrical current 

 itself, were indeed the sources of the current. 



It is the nature of the scientific direction which 

 Magnus pursued in his researches, that they build 

 many a stone into the great fabric of science, which 

 give it an ever broader support, and an ever growing 

 height, without its appearing to a fresh observer as a 

 special and distinctive work due to the sole exertion 

 of any one scientific man. If we wish to explain the 

 importance of each stone for its special place, how 

 difficult to procure it, and how skilfully it was worked, 

 we must presuppose either that the hearer knows the 

 entire history of the building, or we must explain it to 

 him, by which more time is lost than I can now claim. 



