490 Prof. Oliver Lodge on the Paths of 
both at first sight expected them to: they insisted on di- 
verging from the zinc-copper junction, as a Voltaist would wish 
them to. This behaviour is really in perfect accord with my 
theory; though the fact is the cause of Voltaists’ views con- 
cerning seat of H.M.F. They locate the force at the zinc- 
copper junction just because the energy-paths diverge thence 
and appear to start thence. 
Prof. Poynting’s diagram, therefore, not only differs from 
my theory, a thing which is natural and unimportant, but it 
is discrepant with experimental fact. 
Rigid experimental truth would have led him to spread out 
his energy-paths from the metallic junction, rot from the acid 
junction as he has done. ‘True such a proceeding would have | 
landed him in difficulties and apparent absurdity, and he 
would have been compelled to ask, “ How can all the energy 
start from an inert metallic junction?”’ And he might well 
have considered such a conclusion absurd, as it is. 
The reconciliation between sense and fact is simple. The 
lines do, indeed, diverge and spread out from this junction, 
but they do not start thence. They ail start from the zinc- 
acid junction; but they at first creep along close to the surface 
of the zinc, investing it like the coats of an onion; and some 
continue to creep along the copper too, but some do not. 
More lines invest the zinc than the copper ; and the lines in 
excess are given off at the junction, and thence diverge through 
che air. 
An electroscopic experimenter seeking the seat of H.M.F. 
traces these lines, home as he thinks, to the zinc-copper junc- 
ction, and hence regards this as their origin and the seat of the 
torce. Itis not. The lines do not start thence ; they start 
at the real seat of H.M.F’. and source of all the energy, though 
Lheir close-lying continuations between metallic junction and 
acid junction are impossible to trace out experimentally. 
With this preliminary, the diagram of energy-paths for a 
voltaic circuit in Plate IV. almost explains itself. 
The lines are loci of constant electrostatic potential ; and I 
happen to have chosen a circuit whose external resistance is 
twice its internal. The junction of the two metals is placed 
at random wherever its peculiarities may be most conveniently 
observed, The liquid in which the metals are immersed is 
only faintly indicated by the outline of its trough, and, for 
simplicity, it is supposed to be one differing in no electrostatic 
respect from air. Dilute sulphuric acid of a certain strength 
has been shown by Prof. Clifton to satisfy this condition 
almost exactly. 
The particular metals for which the diagram is intended to 
