266 TABLE 296. 



CONTACT DIFFERENCE OF POTENTIAL IN VOLTS. 



Solids with Solids In Air.* 



The following results are the " Volta differences of potential," as measured by an electrometer. 

 They represent the difference of the potentials of the air near each of two metals placed in con- 

 tact. This should not be confused with the junction electromotive force at the junction of two 

 metals in metallic contact, which has a definite value, proportional to the coefficient of Peltier 

 effect. The Volta difference of potential has been found to vary with the condition of the me- 

 tallic surfaces and with the nature of the surrounding gas. No great reliance, therefore, can be 

 placed on the tabulated values. 



The temperature of the substances during the experiment was about 18 C. 



* Everett's " Units and Physical Constants.' 

 pared by Ayrton. 



SMITHSONIAN TABLES. 



The table is from Ayrton and Perry's experiments, and was pre- 



