72 



THE POPULAR SCIENCE MONTHLY. 



makes the loudest sound, and when it becomes silent. You wUl 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 

 sUence 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 XYII., " 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. 



Experiments by which Compound Souicds are analyzed by 

 VIEWING IN A Rotating Mirror the Vibrations op Konig's Mano- 

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



Fig. 51. 



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 J?, 

 which is f inch thick, 1^ inch wide, and 2 inches (51 millimetres) long. 



