180 Prof. Oliver Lodge on the Seat of the” 
He sets himself to disprove the existence of contact-force in 
the most straightforward and obvious manner, and to establish 
the fact that there is no electrical evolution without definite 
and actual chemical action. To this end he announces the 
following propositions :—(1) that two metals in a chemically 
indifferent medium show no electricity; (2) that the potential- 
difference of two connected metals in air is exactly half the 
difference of their heat-combustion energies; and (3) that two 
pieces of the same metal produce contact-electricity as soon as 
they are put into chemically different atmospheres. 
The experiments by which he supports these assertions have, 
every one of them, been elaborately and severely criticised by 
Beetz, Hoorweg, Julius, Schulze-Berge, Von Zahn, Ayrton 
and Perry, Pellat,and Wiedemann ; and his numerical deter- 
minations of contact-force appear to be unique*. 
It is not necessary for me to enter into a discussion on the 
merit of his experiments, inasmuch as the mere fact of the 
existence of so great a body of hostile opinion is sufficient to 
show that they are not of a kind best qualified to produce 
conviction. The theoretical views which led Professor Exner 
to formulate his second statement above, that the potential- 
difference of two connected metals is equal to half the differ- 
ence of their heats of combustion per equivalent, are, I am 
sorry to say, quite unintelligible to me. They depend on the 
hypothetically necessary existence of films of oxide, between 
which and the metal there is supposed to be a considerable 
difference of potential. Perhaps a few quotations from Pro- 
fessor Hixner’s first paper on contact-electricity will render 
his position clearer. His views are but little really different 
of Electricity by the Contact of Heterogeneous Metals ;” December 1879, 
“Qn the Theory of Inconstant Galvanic Elements;” May 1880, “On the 
Theory of Volta’s Fundamental Experiment ;” July 1880, ‘On the Theory 
of Galvanic Elements;” November 1880, “On the Nature of Galvanic 
Polarization ;” July 1882, “On some Experiments relating to Contact 
Theory.” 
* sete, Wiedemann’s Annalen, xii. p. 290; Hoorweg, cbed. xi. p. 138 
(1880), and xii. p. 90; Julius, zbzd. xiii. pp. 276 and 296; Schulze-Berge, 
bid. xv. p. 440, as well as xii. pp. 3807 and 3819; Von Zahn, p. 41 and 
Preface, of his Memoir; Ayrton and Perry, Phil. Mag. 1881, p. 438; 
Pellat, Paris Theses, No. 461, p. 17; Wiedemann, Elektricitat, ii. 
pp. 992-995. : : 
+ I quote from Mr. J. Brown’s translation (Phil. Mag. Oct. 1880) of a 
paper in Wiedemann’s Annalen of the same year, with some abbrevia- 
tions :—“ An investigation concerning the nature of galvanic polarization 
has led me to a quite distinct view of the origin of the so-called contact- 
electricity, a view which will be supported by experiments following. I 
have shown that the original cause of the polarization-current is to be 
sought for, not at the contact of the electrodes with ions liberated on 
