Page:Popular Science Monthly Volume 14.djvu/84

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74
THE POPULAR SCIENCE MONTHLY.

cone to your mouth and sing into it. The sonorous vibrations enter the side A of the box, and, striking on the thin rubber, force this in and out. When it goes in, a puff of gas is driven out of the other partition, B, of the box, and the flame F jumps up. When the sheet of rubber vibrates outward, it sucks the gas into the box B, and the flame F jumps down. Therefore, on singing into the funnel, you will see in the mirror the smooth top-border of the luminous band broken up into little tongues or teeth of flame, each tooth standing for one vibration of the voice on the rubber partition.

Place a lamp-chimney around the flame, should the wind from the twirling mirror agitate it, and be careful not to have the flame too high.

Experiment 113.—Another way of showing the vibrations of the flame is to burn the jet of gas at the end of a glass tube stuck into the end of a rubber tube attached to F. Now sling the tube round in a vertical circle, and you have an unbroken luminous ring; but as soon as you sing into the cone this ring breaks up into a circle of beads of light, or sometimes changes into a wreath of beautiful little luminous flowers, like forget-me-nots. To make this experiment, you will be obliged to have a tube with a larger opening than that at F.

This instrument will afford you many an hour of instruction and amusement. We have only space to show you a few experiments. Others will suggest themselves whenever you use it.

Experiment 114.—Sing into the funnel the sound of oo as in pool. After a few trials you will get a pure simple sound, and the flame will appear as in Fig. 52. Some voices get this figure more readily by singing E.

Experiment 115.—Twirling the mirror with the same velocity, gradually lower the pitch of the oo sound till your voice falls to its lower octave, when the flame will appear as in Fig. 53, with half the number of teeth in Fig. 52, because the lower octave of a sound is given by half the number of vibrations.

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Experiment 116.—Sing the vowel-sound o on the note and you will see Fig. 54 in the mirror. This evidently is not the figure that would have been made by a simple vibration. It shows that this o sound is compound, and formed of two simple sounds, one the octave of the other. The larger teeth are made by every alternate vibration of the higher simple sound acting with a vibration of the lower, and thus making the flame jump higher by their combined action on the membrane.

Experiment 117.—Fig. 55 appears on the mirror when we sing the English vowel a on the note f.

Experiment 118.—Fig. 56 appears on the mirror when we sing the English vowel a on the note c.

Examine attentively Fig. 55. This shows that the English vowel a