488 Prof. Oliver Lodge on the Paths of 
tial, their surfaces becoming charged with the electrostatic 
charges proper for effecting this equalization of potential. 
(3) The air surrounding a pair of different metals in contact 
is therefore in a calculable condition of dielectric strain, espe- 
cially near the junction of the two metals; in other words, 
there is in the air a slope of potential which is most rapid in 
the neighbourhood of the junction, and is there easily observed 
electroscopically. 
(4) This slope of potential observed by Volta, measured by 
Kohlrausch &e. &c., near the junction of any two metals, has 
caused observers to imagine that the metals themselves differed 
in potential, and accordingly to postulate an H.M.F’. or contact- 
force resident at the junction in order to maintain such dif- 
ference of potential in a conductor. 
(5) No such force exists at a metallic junction; because, if 
it did, the passage of a current across such a junction would 
produce violent reversible thermal effects, and none such 
are observed. 
(6) This non-existent force has been imagined, and has been 
utilized to account for the greater part of the H.M.F. in a 
voltaic circuit ; in fact, it has itself been considered to be the 
main H.M.F. in such a circuit ; although it was manifestly 
unable to account for the energy of the current. 
(7) The real seat of the H.M.F. in a voltaic or any other 
circuit must be where conversion of energy, from some other 
form (chemical, thermal, &c., &c.) into the form known as an 
electric current, occurs. 
The object of the present Appendix or Supplement to my 
paper is to supply an accidental omission in the history of the 
subject, and more particularly to exhibit and illustrate the 
mode of regarding conducting circuits which I advocate, by 
diagrams of energy-paths, or erg-odes for those who like 
Greek barbarities. 
The accidental omission from the history of the subject is a 
notice of Dr. Gore’s communication to the Royal Society of 
November 1883*, in which he makes an attempt to bring 
liquids into a thermoelectric series. 
The contact-force between a metal and a liquid is shown to 
vary with temperature; and the results indicate that this 
contact-force is a complex one, not simply depending on the 
chemical relations of the substances in circuit, 7. e. on the cor- 
* Gore, Proc. Roy. Soc. No. 238, vol. xxxvil. p. 251: “Some relations 
of Heat to Voltaic and Thermoelectric Action of Metals in Electrolytes.” 
See also former papers in Phil. Mag. January 1857; Proc. Roy. Soe, 
1878, p. 518, No. 188; 1879, No, 199, and 1880, No. 208. 
