Page:Popular Science Monthly Volume 14.djvu/76

66 in a second in all directions through the surrounding air. They soon reach the drum-skin of the ear. The latter, being elastic, moves in and out with the air which touches it. Then this membrane, in its turn, pushes and pulls the little ear-bones 500 times in a second. The last bone, the little stirrup, finally receives the vibrations sent from the



violin-string, and sends them into the fluid of the inner ear, where they shake the fibres of the auditory nerve 500 times in a second. These tremors of the nerve—how we know not—so affect the brain that we have the sensation which we call sound.

In Chapter V. it is shown that the mechanical actions, which finally result in giving us the sensation of sound, always have their origin in some vibrating body, and that this vibrating body may be either solid, liquid, or gaseous. The author, after showing that the vibrations of a solid (a tuning-fork) and of a liquid (water running through a toy flageolet) give origin to sound, presents to his readers—

—Experiment 33.—The chimneys of student-lamps have a fashion of breaking just at the thin, narrow part near the bottom. Such a broken chimney is very useful in our experiments. At A, in Fig. 25, is such a broken chimney, closed at the broken end with wax. A cork is fitted to the other end of the chimney, and has a hole bored through its centre. In this hole is inserted part of a common wooden whistle. At B is an exact representation of such a whistle, and the cross-line at C shows where it is to be cut in two. Only the upper part is used, and this is tightly fitted into the cork.