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.
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.