of separation, just exactly as if it were suspended from a spring. It
results from this fact that if we displace the brushes a distance equal
to the thickness of one plate of the collector, the active solenoid will
undergo the same displacement, and its longitudinal center will move
away from that of the iron cylinder, and that the attraction exerted
upon the latter will increase. It will not be able to assume its first
value, and equilibrium cannot be re-established unless the cylinder
undergoes a displacement identical with that of the solenoid. Now,
as this latter depends upon the motion communicated to the system
of brushes, we see that, definitively, the cylinder will faithfully
reproduce the motion communicated to the brushes by the hand of
the operator. This apparatus, then, constitutes a genuine electric
servo-motor in which the current is never interrupted nor modified in
quantity or direction, no more indeed than the magnetization developed
in the soft iron cylinder. Everything takes place as if the iron
cylinder were suspended in a solenoid ten centimeters in length that
was caused to rise and fall; with the difference that the weight of the
cylinder exerts no action on the hand of the operator.

[Illustration: ELECTRIC POWER HAMMER.]

These explanations being understood, there remain but few things to be
said to cause the operation of the hammer to be thoroughly comprehended.
The elementary sections constituting the electric cylinder, A B, of the
hammer are 80 in number, and form a total length of one meter. Their
ingoing and outcoming wires end in a collector of circular form shown at
F G. The brushes are replaced by two strips, C E and C D, fixed to the
double winch, H C I, which is movable around the fixed center, C. They
can make any angle whatever with each other, so that by trial there
maybe given the active solenoid the most suitable length. When such