aie REPORT—1885. 
10. Does the energy of Secondary Action contribute to H.M.F. in a cell just 
as much as the energy of Primary Action, or do secondary actions directly 
generate heat ? 
Dr. Wright distinguishes between what he calls ‘ adjuvant’ and 
‘ non-adjuvant ’ chemical actions in a cell—those which help the current 
on, and those which do not. 
Lord Rayleigh raised the same question, at the meeting, in considering: 
a Clark cell; for the sulphate of mercury, being nearly insoluble, must 
certainly be mainly reduced by secondary action if anything like a cur- 
rent is kept going; and yet it seems to contribute to the E.M.F. of the 
cell. 
But one may ask whether the polarisation produced by a moderate 
current in such a cell is not evidence of the speedy exhaustion of the dis- 
solved HgSO,, and of the time taken to replenish the solution from the 
nearly insoluble paste, thus showing that it is after all the dissolved salt 
which is really efficient. 
Moreover, it seems to me that all reversible effects must contribute to 
the E.M.F. Helmholtz’ certainly considers the minor attractions of 
solvents to be as proportionally effective as the main affinities of ions. 
The behaviour of cells which are able to heat or cool themselves, and 
the variation of their E.M.F. with temperature, are of great interest in 
the light of the recent theory of Helmholtz. A result deduced from the 
second law of thermodynamics is pretty surely founded ; but experimental 
verification is always satisfactory, and one can seldom have too much of it. 
The laws that wait examining are these: Measure the total heat, u, 
developed per second in cells of various kinds (internal resistance R) by a 
known current, C; measure also their change of H.M.F. per degree of 
temperature, dE/dt; then see whether 
RC?—JH dE, 
C dt 
Further examine whether each of these quantities is also equal to the 
difference between the observed E.M.F. of the cell and that calculated 
from purely chemical data, viz. to H — = (Je@). 
= (274 + t) 
11. Is specific inductivity a constant, or does it tend towards zero for very 
high strains in the same sort of way that magnetic permeability does ? 
Iam not aware that the capacity of a highly-charged condenser has 
ever been seriously measured. It seems a desirable but difficult thing 
to do. 
12. How does dielectric strength depend wpon density ? 
Considerable work has been done in measuring the dielectric strength 
of different gases at various pressures, but we cannot be said to know the 
law even for air; nor is the truth about the great strength of approximate 
vacua on the one hand, and very high pressure gas on the other, at all 
certain. The dielectric strength of insulating liquids ought also to be 
measured ; and it might be tried how far pressure affects them. 
The effect of pressure upon electrolysis has been worked at, and may 
be said to be fairly understood. The effect of pressure on disruptive 
discharge, and the internal pseudo-conductivity of gases after elimination 
of discontinuities such as cathode-resistance, is more obscure. 
