and by properly proportioning the diameter of the driving pulley and
size of belt to the hammer, the heavy blows are given at a slower rate
than the light ones, owing to the greater resistance which they offer to
the driving belt.

In this hammer the pneumatic connection, the arrangements for the
starting, stopping, and holding up of the hammer, as well as those for
communicating the motion of the crank-pin to the hammer by means of
a rocking lever and movable fulcrum, are similar to those in the
planishing hammer, differing only in the details, which provide double
guides and bearings for the principal working parts.

[Illustration: LONGWORTH'S POWER HAMMER WITH MOVABLE FULCRUM.]

The movable fulcrum, B, Figs. 4 and 5, consists of two adjustable steel
pins, attached to the fulcrum lever, Q, and turned conical where they
fit in the socket, D. The fulcrum lever is pivoted on a pin, R, fixed in
the framing of the machine, and is connected at its lower extremity
to the nut, S, in gear with the regulating screw, T. The to-and-fro
movement of the fulcrum lever, Q, by which heavy or light blows are
given by the hammer, is placed under the control of the foot of the
workman, in the following manner: U is a double-ended forked lever,
pivoted in the center, and having one end embracing the starting pedal,
P, and the other end the small belt which connects the fast pulley
on the driving shaft, A, with the loose pulley, V, or the reversing
pulleys, W and X. These are respectivly connected with the bevel wheels,
W_{1}, and X_{1}, gearing into and placed at opposite sides of the bevel
wheel, Z, on the regulating screw in connection with the fulcrum lever.
When the workman places his foot on the pedal, P, to start the hammer,
he finds his foot within the fork of the lever, U; and by slightly