Page:Popular Science Monthly Volume 14.djvu/82

72 makes the loudest sound, and when it becomes silent. You will find that when it is loudest the faces c, c of the prongs, or the spaces r, r between them, are facing his ear; and when he tells you that there is silence you will find that the edges of the fork, that is, the planes q, q, q, q, are toward his ear.

Our space will only permit one more selection, and this we take from Chapter XVII., "On the Analysis and. Synthesis of Sounds," in order specially to show how Prof. Mayer has placed within the reach of all teachers and students an instrument giving some of the most charming experiments in acoustics. The whole apparatus, if made at home, need not cost over seventy-five cents.

—Take a piece of pine board. A, Fig. 51, 1 inch (25 millimetres)



thick, 1 inch (38 millimetres) wide, and 9 inches (22.8 centimetres) long. One inch from its top bore with an inch centre-bit a shallow hole inch deep. Bore a like shallow hole in the block B, which is inch thick, 1 inch wide, and 2 inches (51 millimetres) long.