Proceedings of the Royal Society. 259 
Among the essential conditions of the phenomena, the author 
particularly adverts to the vast difference of conducting power be~ 
tween the metallic bodies set in motion, and the liquid under 
which they are immersed ; to the necessity of the perfect immisci- 
bility of the conducting fluids, so as to render the transition from 
one to the other quite sudden ; and to a certain chemical or elec- 
trical relation between them. Under these conditions, Mr. H. ob- 
serves, the phenomenon may admit of explanation, from what we 
already know of the passage of electricity through conductors, 
and the hich attractive and repulsive powers of the two electrici- 
ties inter se. A body so highly electro-positive as potassium 
present in mercury may, for instance, have its natural electrical 
state exalted by its vicinity to the positive pole ; and being thus 
repelled, may take the only course the resistance of the metal on 
the one hand, and attraction of cohesion on the other, will permit, 
viz., along the surface, to recede from the positive pole. It may 
even act as a carrier to the positive electricity, which may adhere 
to it too strongly to be transmitted through the mercury, and when 
arrived at the opposite side of the globule may then, by the influ- 
ence of the opposite pole, lose its exalted electrical state. Such an 
explanation, however, is not without its difficulties, and although 
another course is open to us, ‘that of considering the action which 
takes place at the common surface of two unequally conducting 
media, as dependent on a new power of the electric current, bear- 
ing some analogy to magnetic action, yet this, in the present 
state of the investigation, must be regarded not only as a bold, 
but vague hypothesis. 
Thursday, Feb. 19. 
A Paper was read 
On Semi=decussation of the Optic Nerves. By W.H. Wollaston, 
M.D., V.P.R.S. 
In the human brain, {the optic nerves, after passing forward to a 
short distance from their origin in the thalami, become incorporated , 
and from the point of union two nerves are sent off, one to each 
eye. To this united portion the term decussation has been applied, 
