51G 
PROFESSOR J. J. THOMSON ON SOME APPLICATIONS OF 
where A and B are either constants or functions of £ 77 , &c., whose values we do not 
know. From the indeterminateness of A and B, we cannot use these equations to 
determine the absolute velocity of chemical change. We can, however, use them to 
determine the effect on this velocity of any alteration in the external circumstances. 
Thus, suppose that the circumstances are changed so that L is increased by SL ; then, 
if denotes the change in the velocity of we have 
so that 
5 
£ dL ’ 
(76) 
and we can measure all the quantities occurring in this equation, and so compare it 
with experiment. 
If the change in the energy be due to surface-tension, then, if S be the area of the 
surface, T the surface-tension, we have 
i 
A 
di; 
(ST) 
dL 
d£ 
If the change in the circumstances be due to the action of the pressure p, then 
1 
£ dL 
di 
(78) 
where Y is the volume of the mixture and k its coefficient of compressibility. The 
value of dh/d£ for gases is given by equation (14); for solids and liquids by 
equation (74). 
Irreversible Effects. 
§ 21 . So far we have only considered those cases which involve nothing but reversible 
processes, and have left out of consideration the effect of such things as friction, 
electrical resistance, and so on, which destroy the reversibility of any process in which 
they play a part. If, however, as we have done in this paper, we take the view that 
the properties of matter in motion, as considered in abstract dynamics—when all the 
