94 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



nection of Figure 7, its potential excess above Mi will be 8V, just as it 

 was before the last approach of the two plates. 



Now in Figure 6 the Mi end of the connecting wire, being of metal 

 (2), is at potential 8V above M\. Accordingly we have 



whence 



8 V — 8 P = 8 a V + 8 C V -8P= 8 a V+ (8 C V -^ N), 



N . „ (33) 



8 C V = 



N-l 



8P 



As 8P is easily measured, and as N can be made large, we have here 

 indicated a definite, even if not at present entirely practicable, method 

 of measuring 8V. This is the Volta potential difference, chemical 

 action excluded. 



It is evident that the experiments just described would not give the 

 value of 8 a V or even show whether such a difference of potential, due 

 to differential attraction of the metals for the electrons, really exists. 

 If it does not exist, if 8 a V = 0, the Volta potential difference is our 



1 {F r F0. 



e 



But, according to equation (30), - (F 2 -Fi) does not account for the 



e 



whole of the Peltier effect heat, so that, even if 8 a V = 0, the Volta 

 effect is not so related to the Peltier effect that the value of one can 

 be inferred from the value of the other. 



Thcrmo-elcctromotivr-forcc of a Complete Circuit. 



A/WV^ — '-(T) 



Fig. 8 



If we have a complete circuit of M\ and M 2 , we may think of its 



total, or net, electromo- 

 tive force as measured 

 by means of a potenti- 

 ometer, and we may 

 with advantage have 

 this potentiometer ap- 

 plied as in Figure 8,. 

 having contact with M i 

 only, an isothermal 

 stretch of this metal 

 being joined to M 2 at the T' end. The measurement here suggested 



