494 On the Paths of Electric Energy in Voltaic Cireuits. 
junction is the source of all the energy. So far as the external 
circuit is concerned, the metallic junction is the source of the 
energy ; all the energy does in a manner start thence, though 
it does not start originally thence. It reaches the junction 
from another place, its real source, but it travels thither by 
infinitely unrecognizable paths. 
Does the diagram, then, justify modern Voltaists altogether? 
Certainly not. It cuts the ground from under the feet of those 
who have asserted that there is an H.M.F. at the junction of 
zinc and copper—a contact-force which is the cause of the 
observed difference of air-potential in the neighbourhood. 
And it annihilates those who have seen in this imaginary and 
non-existent force any means of propelling the current in a 
voltaic circuit. 
On the other hand, the diagram of course justifies all those 
experimenters who have regarded the zinc-acid junction as the 
main seat of energy-transformation, and therefore of electro- 
motive force. At the same time it exhibits the crudity of some 
of their statements ; and, just in so far as it upholds the truth 
and consistency of the Voltaists with regard to a part of the 
phenomenon, it contradicts some of the opposing statements 
made by chemical theorists with regard to the Volta effect. In 
particular, it lends no support to the customary ‘“ chemical” 
view, which sets down the whole Volta effect as an accident due 
to unavoidable chemical action, and so practically ignores it. 
Imagine the lines investing the metals to be microscopically 
close to them, and then look at the diagram as truly exhibit- 
ing the facts of nature: it irresistibly suggests a voltaic or 
contact theory of the voltaic pile. It was right, therefore, for 
the first observers of voliaic phenomena to found a contact 
theory, and to adhere to it tenaciously, as in some sense true. 
It was also right for later philosophers, imbued with notions 
of energy, to ieel the doctrine that the metallic junction was the 
source of power to be absurd and incomprehensible, and to 
found a chemical theory. 
In the conflict both sides have made mistakes; but it is 
the essence of truth in both views which has given them such 
vitality and endowed their upholders with such energy of 
persistence. 
University College, Liverpool, 
May 17, 1885. 
