50 



Mr. C. V. Burton on 



its Peltier constant, since the conditions are essentially the 

 same in the two cases. 



Thus the law of successive contacts might hold for chemi- 

 cally inactive non-conductors as well as for conductors. 



It might even be that the law is universally true so far as 

 Peltier E.M.F.'s only are concerned ; but of course these are 

 only speculations. 



The following are some analogous properties of Peltier 

 E.M.F.'s and chemical E.M.F/s arranged respectively in 

 parallel columns : — 



Peltieb E.M.F. 



la. When the two substances origi- 

 nally at the same potential are 

 brought into contact an E.M.F. 

 Ej is established across the junc- 

 tion ; this E.M.F. continues to 

 displace electricity across the 

 junction until the E.M.F. due to 

 difference of potentials = — E 1 



2a. The energy required to establish 

 the difference of potentials is 

 supplied by heat absorbed at the 

 junction. 



3a. For every quantity M of elec- 

 tricity which crosses the junction 

 in the direction of the E.M.F. E u 

 a quantity of heat-energy E t M 

 is absorbed at the junction. 



4a. For eveiy quantity M of elec- 

 tricity which crosses the j unction 

 againstthe E.M.F. E u heat-energy 

 E X M is given out at the junction. 



oa. Tne 



tion a heat absorbed at the junc- 

 tne e uring the operation (la) is 

 wliic quivalent of the electricity 

 inm h crosses the junction, deter- 

 j aw ed in accordance with the 

 s of the Peltier effect. 



Chemical E.M.F. 



lb. When the two substances origi- 

 nally at the same potential are 

 brought into contact an E.M.F. 

 E 2 is established across the junc- 

 tion; this E.M.F. continues to 

 displace electricity across the 

 junction until the E.M.F. due to 

 difference of potentials = — E 2 . 



2b. The energy required to establish 

 the difference of potentials is sup- 

 plied by chemical action taking 

 place at the junction. 



3b. For every quantity M of elec- 

 tricity which crosses the junc- 

 tion in the direction of the E.M.F. 

 E 2 , a quantity of chemical energy 

 E 2 M is absorbed at the j unction. 



4&. For every quantity M of elec- 

 tricity which crosses the junc- 

 tion against the E.M.F. E 2 , 

 energy E 2 M is given out at the 

 junction, and appears either as 

 chemical-energy (electrolysis) or 

 as heat. 



5b. The chemical action at the 

 junction during the operation 

 (lb) is the equivalent of the elec- 

 tricity which crosses the junc- 

 tion, determined in accordance 

 with Faraday's Electrolytic La w. 



Sir W. Thomson has deduced a lower limit to the size of 

 atoms by a method which is w 7 ell known. Professor Lodge 

 points out that the limit cannot be assigned with certainty, 

 until the true contact-difference of potentials of the substances 

 concerned is known. But there is another point to be con- 

 sidered. The method assumes that there is a kind of affinity 

 between the molecules of the two metals concerned ; that on 

 contact being made, this affinity gives rise to an E.M.F. 

 which establishes a difference of potential, the necessary 



