On the Paths of Electric Energy in Voltaic Circuits. 487 
by hypothesis molecules are incapable of exerting direct force 
on one another, not being in contact). The medium is exerting 
the force, and will continue to exert it over a certain range, 
hence it possesses the potential energy; when released it will 
do work and transfer its energy to the steel, in the kinetic 
form. If the spring overshoots its mean position, the energy 
is re-transferred and transformed. A perfectly elastic boundin 
ball has all its energy transformed into potential, at the middle 
of every period of contact with the obstacle from which it 
rebounds. 
One case possesses perhaps a little more difficulty, viz. the 
case of a bullet fired into dough—when the body exhibits no 
recoil: how can the energy of the bullet be said to be trans- 
formed into potential now? Only by remembering that heat- 
motion is a vibration of some kind, and that when a vibration 
is excited by a blow or by friction, strain is the effect first 
produced, and afterwards the recoil. Think, for instance, of 
exciting a tuning-fork or a string by bowing or striking it. 
Alternations from kinetic to potential may be rapid in some 
cases, slow in others: no matter; all I have stated is that 
change of form is necessary and universal whenever energy 
is transferred, 7.¢. whenever any kind of activity is exhibited 
by any known kind of material existence. 
University College, Liverpool, 
May 16, 1885. 
LY. On the Paths of Hilectric Energy in Voltaic Circuits 
Appendix to Paper on the Seat of the Electromotive Forces in 
the Voltaic Cell. By Prof. OLIVER LopGE*. 
[Plates IV. & V.] 
HE main conclusions to which I have been led with regard 
to the potentials of metals and the seat of H.M.F. may 
be very briefly stated thus :-— 
(1) A metal is not in general at the same potential as the 
air in contact with it; the difference of potential (or contact- 
force) between any given clean metal and air being calculable, 
at least approximately, from thermo-chemical data, though 
there is no known way of experimentally observing it. 
(2) Putting two metals into contact equalizes their poten- 
* Communicated by the Author. For the sake of completeness it may 
be convenient here to mention that a report of a discussion on Seat of 
E.M.F., at Montreal (Brit. Assoc., Sect. A), is published in the ‘ Electrical 
Review ’ for Nov. 22, 1884, and that a more elaborate discussion on the 
same subject, by the Society of Telegraph Engineers and Electricians, will 
be reported in their volume of ‘ Proceedings’ next issued after the present 
date. 
