210 Scientific Proceedings, Royal Dublin Society. 
Both Machines were then worked, and after a few turns the 
characteristic “sizzling” of the Holtz was heard showing that it 
was charged. The other Machine was then removed, and the 
Holtz continued in full action. This is the method now adopted 
in Trinity College, and it has not been known to fail even under 
the trying circumstances of lecturing to a large class. 
The theory of this method of charging is as follows :—Suppos- 
ing that the comb in connexion with the Charging Machine is 
positively electrified, then positive electricity flows from it to 
the surface of the revolving plate to be neutralized when it 
reaches the second comb by negative flowing from the ground, so 
that one half the revolving plate is charged with positive electri- 
city. : 
Consider its action on the armatures. In the proper position 
of the armatures the general body of any armature is opposite 
the conductor, and the “tongue” pointing in a direction opposite 
to the rotation of the revolving plate, and the action of the posi- 
tive electricity on the first armature is to drive off positive elec- 
tricity from the tongue, through the window in the fixed plate, 
on the back of the revolving plate, leaving the armature itself 
negatively electrified. But the state of things is different at the 
second armature, for as the positive electricity on the revolving 
plate approaches the second armature it meets the tongue first, 
draws out negative electricitity (more than enough to neutralize 
the positive electricity on the back of revolving plate got from 
first armature), leaves the second armature positively electrified, 
and passes on to be immediately neutralized at second unin- 
sulated comb. Thus the armatures go on getting increasing 
charges of opposite electricities until the point is reached when 
the Machine can keep itself going. This is exactly the inverse 
process of the case in which the armatures are supposed charged 
first. 
The great advantage of this method is that in practice it 
effects, with ease and certainty, what was before difficult and 
uncertain. 
