sing the movement of the rack.

Fig. 73. MUTILATED GEARS.--These are made in so many forms, and adapted
for such a variety of purposes, that we merely give a few samples to
show what is meant by the term.

[Illustration: _Fig. 69. Trammel_
_Fig. 70. Escapement_
_Fig. 71. Device for Holding Wheel_
_Fig. 72. Rack and Pinion_
_Fig. 73. Mutilated Gears_
_Fig. 74. Shaft Coupling_]

Fig. 74. SIMPLE SHAFT COUPLING.--Prepare two similarly formed discs (A,
B), which are provided with hubs so they may be keyed to the ends of the
respective shafts. One disc has four or more projecting pins (C), and
the other disc suitable holes (D) to receive the pins.

Fig. 75. CLUTCHES.--This is a piece of mechanism which is required in so
many kinds of machinery, that we show several of the most approved
types.

Fig. 76. BALL AND SOCKET JOINTS.--The most practical form of ball and
socket joints is simply a head in which is a bowl-shaped cavity the
depth of one-half of the ball. A plate with a central opening small
enough to hold in the ball, and still large enough at the neck to
permit the arm carrying the ball to swing a limited distance, is secured
by threads, or by bolts, to the head. The first figure shows this.

Fig. 77 illustrates a simple manner of tightening the ball so as to hold
the standard in any desired position.

Fig. 78. TRIPPING DEVICES.--These are usually in the form of hooks, so
arranged that a slight pull on the tripping lever will cause the
suspended articles to drop.

Fig. 79. ANCHOR BOLT.--These are used in brick or cement walls. The bolt
itself screws into a sleeve which is split, and draws a wedge nut up to
the split end of the sleeve. As a result the split sleeve opens or
spreads out and binds against the wall sufficiently to prevent the bolt
from being withdrawn.

Fig. 80. LAZY TONGS.--One of the simplest and most effective instruments
for carrying ice, boxes or heavy objects, which are bulky or
inconvenient to carry. It grasps the article firmly, and the heavier the
weight the tighter is its grasp.

Fig. 81. DISC SHEARS.--This is a useful tool either for cutting tin or
paper, pasteboard and the like. It will cut by the act of drawing the
material through it, but if power is applied to one or to both of the
shafts the work is much facilitated, particularly in thick or hard
material.

[Illustration:
_Fig. 75. Clutches_
_Fig. 76. Ball and Socket Joints_
_Fig. 77. Fastening Ball_
_Fig. 78. Tri