of Edinburgh, Session 1885 - 86 . 
629 
density in a finite series of terms. The above formula gives the 
maximum value of the polarisation current. So far as I know, 
no observations have been made regarding its variation w r ith time 
from its commencement until the maximum is reached. This 
question is of interest chiefly from a theoretical point of view. The 
object of this note is to describe the result of some experiments 
made on this subject. Platinum electrodes, heated to redness before 
each experiment, were used. The electrolyte was a 5 per cent, 
aqueous solu- 
tion of sulphu- 
ric acid. A 
Helmholtz gal- 
vanometer was 
placed in cir- 
cuit with the 
electrolytic cell 
and the bat- 
tery. The read- 
ing of the gal 
vanometer was 
taken every 
minute from 
the time of 
starting the 
current until 
it apparently reached the stationary value. The results of two of 
these experiments are shown graphically by the subjoined curves. 
The ordinates are proportional to the current-strength, and the 
abscissae represent time. These curves closely resemble the 
logarithmic curve in form. To test how close the correspondence 
is, we may assume the equation 
j = a - bz~ ct 
to be true, when j is the polarisation current, t is the time, and 
a, b, c are constants. In fig. 1, I have taken the point (*85, 1) as 
the origin, and reckoned j downwards to the curve from a line 
drawn parallel to the axis of time through this point. The value of 
