When each coin rings out its whole number, or nearly so, you will have what is known as a harmonic series. Now saw notches in the edges of each one as shown at [A in Fig. 106] and then file them until the tone of each one is just right.
How to Play Them.
—To play a tune with the musical coins spin them on the top of a table—a marble top table is the best—and as each coin dies down[105] and its edge strikes progressively against the surface of the table it will ring out in a clear, loud tone.
[105] If you will look closely at the spinning coin you will see that when it spins fast at first the axis about which it rotates is its diameter and that the coin stands upright. As the coin commences to die down the axis about which it spins gradually begins to shift from the diameter to the center of the coin until finally at the finish the coin is spinning directly about its center. This motion is the same as the processional motion of the earth.
Fig. 106b. how to hold the musical coin to spin it
The coins should be laid in a row on the table and whatever note you want to ring out pick up the coin which will produce it, hold it as shown at [B], and give it a little spin. You can soon learn to spin them with either hand and keep two or more of them going at the same time, when you will have that agreeable combination of tones that is known in music as harmony.
The musical coins are easy to learn to play and at a little distance off they look like real coins and are a very pleasing novelty.