88 
MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
point at 0‘36 inch distance from a plate diminishes the potential of the battery of 8040 
cells by only 4 ^-p -th part, or less than two cells. 
This discharge from the point when positive has mainly to the naked eye a stream- 
like appearance, consisting of a waving line of light surrounded by a very faint sugar- 
loaf luminosity and producing a rattling or strong hissing sound ; from the point when 
negative it consists of a glow of light paraboloidal in form and extending from the 
point to the disc, but much more brilliant at the point, the noise of the discharge 
being much less than when the point is positive. The disc, especially when positive, 
soon becomes covered with a peach-like bloom, and the deposit assumes the appearance 
of Newton’s rings. 
Small as this current is, it is, nevertheless, very manifest from its brightness and 
the rattling or loud hissing noise it produces ; it frequently continues for some 
minutes before the spark actually jumps between terminals placed at the striking 
distance asunder ; the streamer-discharge becomes brighter just before the jump and 
formation of the arc, and this suggested the possibility of particles being carried off in 
increasing quantity from the point to the disc, and thus contributing to the production 
of the spark. In order to test this hypothesis, the terminals were placed at the 
striking distance and a continuous blast from a blowpipe bellows sent between them ; 
Fig. 16. 
this did not, however, have any effect on the length of the spark, but it deflected the 
arc when once it had formed. 
Under the microscope the discharge, from the point when positive, is seen to consist 
of several streams of light, which twist round each other like loosely-bound strands, as 
shown in fig. 16, representing the discharge between the terminals in a horizontal 
discharger. Part of the discharge from the point negative is shown in fig. 17. 
In order to study these discharges, we had constructed for us a microscope (fig. 18) 
with a revolving mirror placed at an angle formed by the two tubes composing the 
