384 Trowbridge and Penrose — The Tho 



i Effect. 



hound, parallel, against each face of the thermopile, 

 lated from it by thin pieces of mioa. Especial care was taken 

 to fasten the carbons firmly so as to prevent any motion from 

 the passage of the current. The pencils were placed perpendic- 

 ularly, the lower ends in two vessels of mercury, surrounded 

 by melting ice ; the upper ends were at the temperature of the 

 air. The upper ends were electrically connected and the wires 

 from a battery of three Grove cells were placed in the vessels of 

 mercury. The thermopile was connected with a reflecting gal- 



When the system had reached a condition of thermal equilib- 

 rium, the current from the battery was passed, and the observa- 

 tions were made. The vessels of mercury and the corresponding 

 pencils are denoted by "a" and "6." The current entered 

 alternately in "a" and b, v the deflections of the galvanometer 

 being taken, in each case, every half minute. The deflections 

 showed that the pencil "a " was warmer than "ft," but the dif- 

 ference of temperatures was greater in one case than in the other. 



The following table represents the results of two sets of 

 experiments. The small numbers at top show which column 

 of each pair was taken first. 



F 



rstE^erimen 





Second Experiment 



c-p.*- 



°-w- 



1 ., , :; ; ",:;p, 



"-a*** 



c™,„ M , 



S' 



a" 



r' 



S3 



20-8 

 347 



m ' 



5 



53 



33-0 



K 



i" 



SI 



S 





32-8 



11 





34-3 



g 



g 



1-8 



21-7 



216 



24 



3-3 



HI 



32-6 



304 



11 



23-0 ' 



21-7 



3 



3 



S3 



210 

 39-8 



HI 



11 



23-5 ' 



£5 



20 





45-8 



s' 



5 



10 









31 



