Fortunately, you can satisfy yourselves on this point without any other materials than a cardboard disc and a piece of string. On this disc paint in small sections the colors of the spectrum, repeating them four or five times in the following order: red, orange, yellow, green, blue, indigo, violet.
That the experiment may be entirely successful, the sections must be marked off according to the following scale of width of section. Let orange, next to the circumference represent 2: then
| Red will be represented by | 5 | |
| Orange | “““ | 2 |
| Yellow | “““ | 5 |
| Green | “““ | 4 |
| Blue | “““ | 5 |
| Indigo | “““ | 3 |
| Violet | “““ | 5 |
Now, in any diameter of the disc bore two holes not too near the edge. Through them pass a piece of string, and knot the two ends together. Take hold of the string with both hands, and make the disc spin round.
Then extend and approach the hands alternately to give a very rapid movement to the disc. When revolving rapidly enough you will not be able to distinguish the separate colors. They all become blended into white light.
The Mysterious Apple.
Pierce an apple in such a manner as to obtain two holes tending toward the middle, and forming a pretty large angle as shown in the figure. Two quills or tin tubes should be inserted to make the inside passages smooth. Pass a string through the hole and your apple is prepared for a little trick, which, you may be sure will astonish all persons before whom you practice it, and who of course are not yet initiated.
You fasten one extremity of the string to your foot, and take the other in your hand so as to produce at will the rigidity of the string. You can then command the apple to go down, or to stop, and it will obey your order immediately. Indeed, when you straighten the string, the part which enters the apple pushes against the angle formed by the two passages, and by the pressure, holds the apple. When on the contrary you let go a little, you take away the rigidity and the apple glides down.