[Fig. 122.—Bon jour.]

[Fig. 123.—Experiment showing sounding bodies are in vibration.]

[Fig. 124.—Method of registering vibrations of a tuning fork.]

[Fig. 125.—Way line made by a bristle attached to a tuning fork prong in vibration when passed over smoked glass.]

[Fig. 126.—Illustrating the action of air waves.]

[Fig. 127.—The vocal chords in position for making a sound.]

[Fig. 128.—The vocal chords when relaxed.]

[Fig. 129.–Koenig's manometric flame apparatus.]

[Fig. 130.—Appearance of manometric flame in revolving mirror.]

[Fig. 131.—Diagram of a telephone transmitter.]