y inaccuracy will make the lever twist
as it moves. To prevent the pivot cutting into the wood, screw to the top
of C a brass plate bored to fit the pivot accurately. The strain will then
be shared by the screws.

The horns of A should be long enough to allow the outside of the fixed grip
to be 2-1/4 inches from the inside of the handle.

The balance is secured first to the lever by a pin driven through the eye
of the hook, and then to B by a 3-inch screw passed through the ring. The
balance should just not be in tension.

When the apparatus is so far complete, test it by means of a second balance
applied to D. Set the scale-marker at zero, and pull on the D balance till,
say, 35 lbs. is attained. If the fixed balance shows 7 lbs. on what is
meant to be a 5 to 1 ratio, the setting of R relatively to P and Q is
correct. If, however, there is a serious discrepancy, it would be worth
while making tests with a very strong balance, and establishing a corrected
gradation on a paper dial pasted to the face of E.

For twisting tests we need a special handle (see Fig. 164), which is
slipped on to the pivot and transmits the twist to L through a pin pressing
on the back of the lever. The stirrup is made out of strip iron, bent to
shape and drilled near the ends for the grip spindle. To the bottom is
screwed and soldered a brass or iron plate, into the underside of which the
pin is driven.

[Illustration: FIG. 164.--Handle for twisting test.]

To prevent the handle bending over, solder round the pivot hole 3/4 inch of
brass tubing, fitting the pivot closely.

Tests.--Grip tests should be made with each hand separately. The
baseboard should lie flat on a table or other convenient support, and be
steadied, but not pushed, by the hand not gripping.

Twisting tests may be made inwards with the right hand, and back-handedly
with the left. The apparatus is stood on edge, square to the performer,
resting on the horns of A and a support near the balance.

Finger tests are made by placing the thumb on the front face of B, and two
fingers on the farther side of the lever, one to the left and the other to
the right of the tail of the balance.

XXX. LUNG-TESTING APPARATUS.

The capacity of the lungs, and their powers of inspiration and expiration,
can be tested by means of easily constructed apparatus which will interest
most people who are introduced to it. The reduction of the capabilities of
the lungs to figures affords a