596 
Proceedings of the Royal Society 
magnetic shell, it can exert no magnetic force outside the shell ; 
and hence the current will have no effect upon any system of 
permanent magnets that may be employed to produce a stronger 
magnetic field surrounding the needle. 
PRIVATE BUSINESS. 
Mr James Tait Black and Mr E. Peirson Eamsay were balloted 
for, and declared duly elected Eellows of the Society. 
Monday, 21st April 1884. 
Sir william THOMSON, Hon. Vice-President, 
in the Chair. 
The following papers were read by Honorary Fellows now 
in Edinburgh : — 
1. On Galvanic Currents passing through a very Thin Stratum 
of an Electrolyte. By Professor H. von Helmholtz. 
If one closes a galvanic circuit containing a small battery, the 
electromotive force of which is not able to decompose water, and a 
voltameter with two platinum plates dipping into water acidulated 
with sulphuric acid, the current has a great intensity in the first 
moment, and diminishes at first very rapidly, afterwards slowly. 
At last its intensity approaches to zero more and more, but it never 
ceases completely. The more sensitive the galvanometer by which 
you measure its intensity, the longer the time during which you are 
able to observe the deflection of the needle. If the electrolytic fluid is 
in contact with atmospheric air, it is easy, even with a galvanometer of 
simple construction and moderate sensibility, to observe that at last 
a feeble residue of current remains, keeping a nearly constant inten- 
sity. This intensity, however, is increased by the slightest motion 
of the fluid, also by feeble motions produced by changes of tempera- 
ture. Under these conditions, it is nearly impossible to determine 
by measurement regular relations between the electromotive force. 
