72 . RESEARCH COMMITTEES.- 
which a sound thermodynamical theory of the cell was first 
propounded, Four years later, Helmholtz published the first of a 
series of memoirs covering between them nearly the whole of the 
subject. A report “On the present state of our knowledge of 
the thermodynamics of the voltaic cell” is practically a summary 
of the work of Helmholtz and his successors. 
A word should be said as to the form this report has taken. 
Tt practically amounts to a sketch of the theory of the subject, 
pointing out in regard to each of its divisions the shares con- 
tributed to it by the different investigators quoted. In this way 
the advantage is gained of a uniform notation in the development 
of the theory ; it is hoped that this will render the work more 
valuable than a string of abstracts of papers arranged in order of 
time would be. 
2. The Potential Energy of a Reversible System. 
Let the intrinsic energy of any reversible system of bodies be 
denoted by U, heat supplied to the system by Q, temperature by 
T, entropy by ¢, and the * parameters——independent of each 
other and of the temperature—which define the state of the 
system by p,, p., &e.; let the external work done in the variation 
dp, of any parameter p, be denoted by P., dp, ; 
then the first law of thermodynamics may be written— 
AQ= sy aT +301 5 +P. bap, .. (1) 
and the second law is expressed Ae 
Ley OF 1 sn oU ) 
dja eed Dito Saisp thle (2) 
fs 
From (2) we obtain at once 
ab tO ee 
op, ‘TY Cop, 
re Ss OT a, ae «an. @) 
es I Car 
whence 
cp 6U 
bp, Os P. ) 
Now suppose that the transformations considered all take place 
a omar then (4) may be written 
5 (Td De aus wee .. (Lbis) 
* 7 must be finite and integral, but may be as large or small as we please. In ordinary 
thermody: namics n=1, and p. =volume of unit mass. 
