188 Mr. Herschel on certain motions produced in 
current from the point of contact instead of to it, and this 
ceases the moment the contact becomes perfect by amalga- 
mation, and cannot be renewed but by cutting off the amal- 
gamated end, and making a fresh contact. 
45. When mercury is electrified in contact with the positive 
pole under certain metallic solutions (nitrate of copper for 
instance), and the circuit broken, removing both wires, the 
current continues feebly for some time after the electric 
power is withdrawn, in the same direction (viz. from the 
point (z) opposite to the negative pole. By degrees, it grows 
more forcible, and a film formed during the electrisation is 
swept along to the point (c) opposite the former position of 
the positive wire, where it accumulates, leaving at length, 
the portion of the surface at % quite bright As soon as this 
happens, the currents increase considerably in strength, and 
radiate with great violence from the point z. This spontaneous 
action continues often for a long while. If the negative pole 
be made to act in succession, opposite to two points z, z\ of 
the mercury, and be then quickly withdrawn and the circuit 
broken, both these points become centres, from which spon- 
taneous currents radiate simultaneously in all directions. If 
the negative pole be made to act vertically over a large flat 
surface, when the circuit is broken, a violent spontaneous ra- 
diation emanates from the point immediately below the place 
where it was situated. 
46. If the wires be only withdrawn so as to complete the 
circuit in the liquid, the film formed during the contact of the 
positive pole is swept to the point c, opposite that pole ; and 
a violent current is established, radiating from z to c. If this 
be suffered to continue some time, and the circuit be then 
