132 Dr. Wright on the Behaviour of Mercury as an Electrode. 
solution. The mercury extended itself, and was driven with 
violence in the direction of the zinc. At the same time the 
strong currents were set up in the solution which have been so 
fully described by Herschel and others. 
Experiment 9.—A common dinner plate was inverted, and a nar- 
row strip of silver cemented acrossits bottom. This strip served 
to retain a large pool of mercury in the centre of the plate. A 
solution of iodide of potassium was now poured on the plate, and 
two iron wires dipping into the liquid transmitted the current of 
twelve small Daniel’s cells across the plate and the silver strip. 
The mass of mercury immediately commenced flowing to and 
fro between the wires, touching and receiving an impulse from 
each wire alternately. By employing several pounds of mercury, 
the last experiment might be rendered a very striking illustration 
of the galvanoscopic properties of mercury before a large audience. 
Undulatory Motions of Mercury. 
Two globules of mercury immersed in a solution of chloride of 
sodium were connected with the ends of the primary wire of an 
electro-magnetic coil machine. When the machine was slowly set 
in motion, the mercury undulated in two directions so as to repre- 
sent across. Increasing speed in the action of the break caused 
the metal to assume successively the form of a star with six, 
eight, twelve, or more rays. Occasionally, also, these stars 
would revolve slowly on their centres. 
A large pool of mercury under the same circumstances had 
its entire surface thrown into innumerable waves, which showed, 
by their mutual interference, figures of remarkable complexity, 
when examined by a reflected beam of light. These figures were 
always constant for the same speed of break, power of battery, 
and shape of the mercury. 
Having noticed on several occasions the occurrence of un- 
dulatory motions in mercury when traversed by a constant cur- 
rent, I endeavoured to reproduce these motions, but for some 
time in vain. At last I found that they took place in a solution 
of chloride of sodium containing a very small quantity of sul- 
phuric acid; in the former of which solutions mercury expands, 
while in the latter it contracts. This beautiful experiment as 
perfected was performed as follows :—A plate of zinc three inches 
in diameter, having a wire soldered to it, is sewed up in muslin 
and cemented in the centre of a white dinner plate. A quantity 
of mercury is then poured into the plate until it lies as a flnid 
ring round the bottom and at about two inches distant from the 
zinc. The metals are now covered with a clear saturated solution 
of chloride of sodium. The wire soldered to the central piece of 
zinc is connected with the positive pole of a platinized zine 
