152 PHYSICS. 
receiving it on a series of metal points, placed in the current of steam, and 
connected with the floor by a conductor. 
3. Of Combined or Disguised Electricity. 
When two conductors, charged with opposite electricities, are separated 
Ly a tolerably thin layer of air, the two fluids mutually attract and retain 
each other, so that neither gives evidence of its presence by any specific 
action, and either may be brought into contact with a conductor without 
passing off through it. The two opposite fluids are then said to be 
combined, disguised, or paralysed. The mutual retention is more complete 
if some other insulator, as glass or resin, be used instead of air, which, on 
account of its rarity, cannot prevent the union of the two fluids by the 
passage of a spark. This separation by glass occurs in the Franklin plate 
(pl. 20, fig. 33). By this is to be understood a plate or pane of glass, 
coated on both sides with tin foil to within a few inches of the edge. If 
now one side be charged with positive and the other with negative 
electricity, the two fluids will exert a powerful attraction on each other. 
For this purpose it is only necessary to bring one coating in contact with 
the prime conductor of an electric machine, and to connect the other 
coating with the earth. ‘Turning the machine the electricity of the glass 
cylinder or plate becomes decomposed, the positive remaining, the negative 
passing off to the rubber, and thence along the connecting chain to the 
ground. The positive fluid of the glass then decomposes the electricity of 
the prime conductor, attracting the negative, which, mixing with the 
positive on the glass, restores the equilibrium ; this, however, is immediately 
disturbed again by the continued friction of the rubber. The same 
operation now takes place between the positively electrified prime 
conductor and any body with which it is in contact, the Franklin pane 
for instance. The negative electricity is attracted to the positive of the 
conductor ; the one side then of the pane is charged with the positive fluid. 
This acts by induction on the combined fluid of the opposite ccating, and 
drives off its positive electricity through the conducting medium into the 
ground, retaining the negative. The two sides will thus be oppositely 
electrified. But, although the two fluids thus mutually retain each other, 
one or the other will always be in excess, which will be drawn off by 
touching with the finger or other conductor. The other side will then 
possess a surplus which may also be drawn off in the same manner; and 
thus by applying the conductor a great many times alternately to the two 
sides of the pane, it may gradually be deprived of all its free electricity. 
The same restoration to equilibrium might have been effected by the 
instantaneous combination of the two fluids through a discharging rod 
(pl. 20, fig. 34). This consists of two jointed arms of brass, be, cb’, with a 
glass handle, m, m’, to each arm, as in the figure, or else a single glass 
handle placed at the joint. The arms are tipped with balls which may be 
approximated or separated by the motion of the arms on the hinge-joint at 
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