674 ALEXANDER MACFARLANE AND R. J. S. SIMPSON ON THE 
uniform rate, the index remained steady ; when it was turned faster, the index 
gave a greater reading ; when slower, a less reading. Sometimes the current 
passing appeared to break the thread; when that happened, the electricity 
had an opportunity of beginning to pass in a different mode. 
Three other modes of discharge were observed-—by motion of the liquid; by 
a disruptive discharge; and by convection by means of gas-bubbles. When the 
disc was at the height of 4 or more millimetres above the plate, the surface of 
the oil of turpentine became agitated; while the behaviour of the index of the 
electrometer showed that the charge was being rapidly, but not instantaneously, 
lost. This agitation of the liquid ceased when any other kind of discharge 
began. “When the Holtz machine was turned for some time with its conductors 
in contact, and the contact then suddenly broken, a circular ripple was first 
observed of diameter about equal to that of the disc, and then the agitation pro- 
ceeded to extend over the surface. The existence of the agitation appeared 
to depend on the nearness of the upper electrode to the surface of the liquid 
(which was generally 4 centimetres deep), as well as on the amount of 
charge. The surface assumed a different form, according as the charge 
was positive or negative. When the charge was positive, the liquid rose up 
round the rod of the receiver ; when negative, the liquid rose up the edge of 
the vessel, sometimes up to and over the rim—a height of about 5 centimetres. — 
On one occasion, when the surface had been agitated for some time, and when, 
in consequence of diminished air-pressure, a considerable quantity of turpentine 
vapour must have been present, a red smoky flame was observed for an instant 
on the surface of the liquid. No luminous discharge was observed at the 
time. é 
When there was no chain of solid particles betweeu the plates, it was generally : 
possible to get a disruptive discharge, similar to that through air, even though — 
the surface of the liquid was in great commotion. The spark was vertical and 
dazzling white ; threadlike, sinuous, and sometimes forked, when the Leyden 
jars were off the conductors of the Holtz; but thicker and more direct when 
the jars were on. The flash gave a continuous spectrum, and sometimes ap- 
peared tinged with crimson, like the sparks through hydrogen, especially at the 
negative electrode. The sound accompanying the discharge was more intense 
than the sound accompanying the discharge through air under the same condi- 
tions. The index of the electrometer indicated that the discharge was complete. 
The disruptive discharge was accompanjed by the formation of bubbles of gas. 
These were always attracted to the negative plate. When the electrification 
was neutralised, they of course adhered to the under surface of the disc ; when 
the disc was electrified negatively, they adhered with still greater firmness; 
when positively, they were repelled so as either to remain suspended in the 
liquid, or to adhere to the lower electrode, according to the greater or less 

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