186 Prof. Oliver Lodge on the Seat of the 
clear a form is in itself a powerful argument for the views 
held by Maxwell *. 
Prof. Fleeming Jenkin, in the last edition of his ‘ Electricity 
and Magnetism,’ p. 216, endeavours to reconcile the contact 
and chemical theories. Acccrding to the chemical theory, 
the H.M.F. ofa cell ==(J@e); according to the contact-theory 
itis C/L+L/Z+Z/C. On these undoubted facts he pro- 
ceeds to found a number of statements which are true, though 
scarcely simple; in fact they perhaps rather tend to compli- 
cate what may be held to be a simple matter. 
Schonbein, in a letter to Faraday published in the Philoso- 
phical Magazine for 1838, throws out a remarkable sugges- 
* Although this article is, or ought to be, easily accessible to everybody, 
there is one important suggestion in it which it is as well to quote, viz. 
that contained in the following sentence :—“ We are so ignorant of the 
nature of the motion which is the essence of the electric current that the 
very form in which we have put the question [as to the locality of E.M.F. | 
may be misleading. If this motion be in the surrounding medium, as 
there is great reason to believe it to be, it would not be-surprising to find 
that speculations as to the exact locality of the E.M.F. i the circuit were 
utterly wide of the mark.” Prof. Willard Gibbs suggested something of 
the same sort at Montreal, though in a rather vaguer form. I do not 
myself feel any doubt that a precise location can be given to the H.M.F., 
notwithstanding that much of the current energy exists in the medium. 
The most complete attention to the distribution of energy in circuits which 
has yet been bestowed on the subject has been given by Prof. Poynting in 
his remarkable memoir (Phil. Trans, 1884), and he therein locates the 
E.M.F. of a battery exactly where I do myself. 
+ Except, indeed, a doubtful statement at the end of Number 2 and an 
erroneous bit of reasoning at the end of Number 4, though the conclusion 
drawn is correct. 
t Schdnbein, Phil. Mag. vol. xii. pp. 225 and 311. The two most 
striking sentences are here extracted :— 
‘‘ Before closing my letter, allow me to communicate to you in a general 
manner the view which I have taken of the subject in question. In the 
first place, I must tell you that I am by no means inclined to consider 
mere contact in any case as the cause of the excitement of even the most 
feeble current, I maintain, on the contrary, in accordance with the prin- 
ciples of the chemical theory, that any current produced in a hydro- 
electric voltaic circle is always due to some chemical action. But as to 
the idea which I attach to the term ‘chemical action,’ I go further than 
you and M. de la Rive seem to go; for I maintain that any tendency of 
two different substances to unite chemically with one another must be 
considered as a chemical action, be that tendency followed up by the 
actual combination of those substances, or be it not; and that sucha 
tendency is capable of putting electricity into circulation.” 
And on page 314 he explains this last phrase, which he has elsewhere 
called a “current of tendency,” thus :— 
“As what I term a current of tendency is no doubt in some cases 
nothing but that electrical state which the Voltaists consider to be the 
effect of their ‘force electromotive,’ or of contact, it appears to me that, 
from some of the facts above stated, a specific and most important con- 
clusion regarding the theory of the pile can be drawn, Even if we 
