298 The Rev. Dr. Rosrnson on the Effect of Heat in lessening the 
instance, an antagonist of affinity, while at a lower temperature it is auxiliar to it, 
there must be a certain portion of the thermometric scale where its action is null, 
and which may be expected to present some peculiar facts that might give an 
insight into the theory of these attractions. This speculation might perhaps be 
verified by a method which I had been applying for some years during the few 
moments which I can spare from other pursuits. It is an application of the pro- 
cesses and instruments described by Mr. Wheatstone in his Memoir on deter- 
mining the Constants of a Voltaic Battery (Phil. Trans. 1843), to give a measure 
of the affinity which combines the elements of an electrolyte, by measuring the 
diminution of electric intensity which its decomposition causes in the battery. It 
is much to be regretted that Mr. Wheatstone himself, or some other of similar 
acquirements, has not followed up this part of electro-chemical science; for it 
seems capable of giving in many instances those numerical values of affinity which 
are required to bring chemistry more fully within the domain of mathematical 
investigation. A very brief explanation of it will serve both to explain my own 
communication, and, | hope, to inspire in such members of the Academy as may 
not be acquainted with the theory on which it is based, a wish of becoming more 
familiar with it. 
It is well known that the energy of a voltaic current is expressed by the 
formula 
E 
Raia 
in which the numerator represents the intensity of its exciting cause, and the 
denominator the sum of the resistances which oppose its transmission. The theo- 
retical reasoning on which it is based is, of course, in some degree, hypothetical ; 
but it has received most ample verification from experiment in every instance of 
its application. The symbol x denotes the sum of the resistances of the fluids 
interposed between the metals of the battery; it varies with their composition, 
and differs in no respect from that of metals, being like them directly as the length 
of the conducting medium, and inversely as its transverse section. The remain- 
ing resistances, being metallic, are represented by 7; both can be expressed 
directly in revolutions of Mr. Wheatstone’s Rheostat. 
The quantity © denotes a change of electric condition produced by the che- 
mical changes occurring in the circuit, and strictly proportional to their inten- 
