_A Pair of Scales._--Moreover this is a toy which can be made quite
accurately with the aid of a few quite ordinary materials. To a pair of
scales--or a balance, as it is sometimes called--there are generally
these parts: (1) a balancing arm, generally called the beam; (2) an
upright standard on which the beam is supported; (3) two scale pins, and
chains (or strings) to suspend them; (4) a base board to which the
upright standard is fixed. Fig. 72 shows the sort of thing we mean.
[Illustration: FIG. 72.]
Now of these things not one presents any real difficulty. For the base
board any piece of wood about a foot long, 5 in. wide, and 3/4 in. thick
will do quite well. For the upright standard you require a piece of wood
about 9 in. long and 1 in. square--one end of which must be fixed to the
base board. The method of doing this will depend very largely on your
degree of proficiency in the art of carpentry. If you know how to make a
mortise and tenon joint, that will be the most suitable. If you cannot
attain to that, then perhaps you can make a hole just as large as the
standard, and sink the standard in the base. If you are not at all an
expert, then you must just nail or screw your standard to the centre of
the base.
Before you do this, however, there is something to be done to the other
end. You must cut a slot 1/2 in. wide and 1-1/2 in. deep (Fig. 73_a_);
then you must cut away small triangular pieces from the centres of the
tongues left (Fig. 73_b_); and finally you must nail to the sides of the
V so formed two little strips of tin (Fig. 73_c_).
[Illustration: FIG. 73.]
The next thing to be constructed is the "beam." For this you will need a
piece of fretwood (or other thin wood) about 9 or 10 in. long and about
1 in. wide. To support this on the metal V pieces you will need a thin
piece of steel--such as a piece of an old pocket-knife blade. This will
be driven through the centre of the beam, and will project equally on
either side (Fig. 74). Remember, it must fit tightly; so when you cut
the slot for it, do not make it too wide.
[Illustration: FIG. 74.]
For the scale pans two canister lids will do quite well. Bore three
holes in each of the rims--measuring off the distances with a compass,
so that the holes are equally far apart, and suspend the pans by means
of three strings passing into holes in the ends of the beam. If, when
you have completed the work, the beam does not hang perfectly
horizontal, then you must add weight or subtract weight from one side or
the other. You can do this by paring off tiny pieces from the end of the
beam, or you can stick on dabs of sealing wax till the correct balance
is obtained.
If you cannot get any proper _weights_, then it is not a very difficult
matter to make some. To do this, all that you need is to get some
cardboard and a supply of sand, and to borrow a complete set of weights.
First of all make a number of little cardboard cubes, having sides
varying from 3/4 in. to 3 in. Draw each one out on cardboard (Fig. 75);
cut it out; and bind up with gummed tape--leaving one side ungummed. On
one pan of the balance put this thing, and on the other pan put a
proper weight (say 1/2 oz). Now pour in sand into the little cube until
it exactly balances the correct weight. When it does, wet the binding,
and stick down the remaining side. Finally print the correct weight on
one face of the cube.
[Illustration: FIG. 75.]
In similar fashion you can proceed to make all the different weights
that you are likely to require, from 1/2 oz. upwards. While not very
substantial, these little weights will last quite a long time, if they
are handled with care.
Engines of all sorts are always fascinating to boys and girls, and later
on we shall describe some excellent ones. At this point we wish to
describe what is possibly one of the simplest forms of engine known, and
certainly one of the earliest. It is the engine driven by a flanged
wheel, which itself is made to turn by the weight of something falling
on the flanges. The commonest form of this wheel is the water wheel,
where the weight of the water falling on the wheel causes the
revolution.
As water is generally a "messy" thing to operate with, especially on
such a contrivance as this, we have substituted something else.
For the working of very light toys, sand provides an alternative motive
power. If a flanged wheel be made after the fashion of a water wheel,
and a steady stream of sand allowed to descend on to the flanges, then
the wheel will rotate as long as the supply of sand lasts, and the power
may be transmitted by pulley wheels for the working of some simple
mechanism.