118 
Proceedings of Boy at Society of Edinburgh, [jan. 
3. On Transition-Resistance and Polarisation. 
By W. Peddie, B.Sc. 
In a paper communicated to this Society last Session, I gave an 
empirical formula representing the relation between current-strength 
and time when platinum plates are used for the passage of a current 
through acidulated water, the electromotive force being that of a 
single Daniell cell. As is well known, we can look upon the 
electrodes as condensers of very great capacity. If E be the 
electromotive force of the battery used, while e is the reverse 
electromotive force of polarisation, and r, x, and c are the values of 
the resistance, the current-strength, and the capacity respectively, 
the equations of conduction through the condenser are as follows: — 
E - e = 
e de 
R being the resistance of the dielectric. If, in the 'case we are 
considering, no decomposition of the liquid occurs, we may suppose 
R to be infinite. Hence the second equation becomes 
and we get for the law connecting current-strength and time, the 
relation 
where x^ is the value of x when ^ = 0. But the curve represented 
by this equation does not represent the actual variation of x with 
time. Hence, either r or c must vary, or both must vary simul- 
taneously. 
In a paper also communicated last Session, I showed that there 
is a very considerable transition-resistance at the surface of platinum, 
and that this resistance goes on slowly increasing as the time that 
has elapsed after heating the platinum to redness increases, but the 
law of increase is unknown. I have made the assumption that the 
rate of increase is proportional to the excess of the final value of 
the resistance over its value at the given time. If we use R to 
