Trowbridge and Penrose — The Tho 



Effect 



3S0 



the temperature of the air, 15° C; the other at a constant red 

 heat by means of a Bunsen burner. The metal was heated in 

 this way from 9 a. M. to 3 p. m., until it reached a condition of 

 thermal equilibrium, as shown by the galvanometer. The 

 scale of the galvanometer was then moved until the spot of 

 light came to 0. The current from the Grove cells was then 

 passed for one minute, alternately in opposite directions, and 

 the deflections of the galvanometer were read every quarter of 

 a minute. Before the direction of the current was changed the 

 circuit was each time broken, and the spot of light was allowed 

 to fall to 0. The following table gives the results. The col- 

 umn marked "C-H" gives the deflections when the current 

 was ) Kissing from cold to hot. The small numbers show which 

 I hen first. 



7-2 7-5 70 7-2 5-8 6-7 6-2 6"5 7-0 



7-6 7-6 7-3 7-7 6'1 7'3 65 6-8 7-2 



From this table it is obvious that more heat is evolved by a 

 constant current per unit time in passing from the cold to the 

 hot end of the nickel, than in passing in the opposite direction. 

 The Thomson Effect in pure nickel is consequently negative; 

 i. e., heat is absorbed by a current in passing from hot to cold, 

 and evolved in passing from cold to hot. The above results 

 were confirmed by many similar experiments, as will be seen 



was next determined to find whether the Thomsc 

 reversible ; that is, whether the heat absorbed by 

 iissing across a section of temperature t wa^ equi 

 evolved by the same current when passim* in the 

 tion across the same section. This subject has i 

 ngs on the thermodynamic;,! theory of thermo-el 





of lie 



six Grove cells was passed as hHW. and the deflections «>f tho 

 galvanometer were observed every half-mmute. The apparatus 



before. Column 

 eflections. One end of the nickel was n 

 . After one hour it reached a condition 

 and the current from the Grove cells v 

 opposite directions. The deflections i 



