itted with a sliding index, I, in the form of a
1/4-inch strip of tin bent over at the ends to embrace the edges of the
balance.

CONSTRUCTION.

[Illustration: FIG. 162.--Plan of strength tester.]

[Illustration: FIG. 163.--Grips of strength tester.]

As the pressures on the machine are high, the construction must be solid
throughout. The lever frame, A, and pivot piece, C, should be of one-inch
oak, and the two last be screwed very securely to the baseboard. The shape
of A is shown in Fig. 163. The inside is cut out with a pad saw, a square
notch being formed at the back for the lever to move in. The handles of an
old rubber chest expander come in useful for the grips. One grip, D, is
used entire for attachment to the lever; while of the other only the wooden
part is required, to be mounted on a 1/4-inch steel bar running through the
arms of A near the ends of the horns. If a handle of this kind is not
available for D, one may substitute for it a piece of metal tubing of not
less than 1/2-inch diameter, or a 3/4-inch wooden rod, attached to an eye
on the lever by a wire passing through its centre.

A handle, if used, is joined to the lever by means of a brass plate 3/4
inch wide and a couple of inches long. A hole is bored in the centre
somewhat smaller than the knob to which the rubber was fastened, and joined
up to one long edge by a couple of saw cuts. Two holes for good-sized
screws must also be drilled and countersunk, and a socket for the knob must
be scooped out of the lever. After making screw holes in the proper
positions, pass the shank of the knob through the slot in the plate, and
screw the plate on the lever. This method holds the handle firmly while
allowing it to move freely.

The lever tapers from 1-1/2 inches at the pivot to 5/8 inch at the balance
end. The hole for the pivot--5/16-inch steel bar--should be long enough to
admit a piece of tubing fitting the bar, to diminish friction, and an
important point, be drilled near the handle edge of the lever, so as to
leave plenty of wood to take the strain. The last remark also applies to
the hole for the balance pin at Q.

The balance support, B, and the pivot piece, C, are 2-1/2 and 2-7/16
inches high respectively. Run a hole vertically through C and the baseboard
for the pivot, which should be 4-1/2 inches long, so as to project 1 inch
when driven right home. Take some trouble over getting the holes in L and C
quite square to the baseboard, as an