ACOUSTICS. 65 



tube, it will disturb the flame so much as to give a dis- 

 tinctly serrate image either upon the screen or in the 

 plain mirror. The annexed figure will give an idea of 



Fig. 41. 



the arrangement mentioned : a is the tube for produc- 

 ing sounds, in b is the funnel with tissue-paper over its 

 mouth, c rubber connection to the blow-pipe d, which 

 opens upward into the flame from the candle <?. 



THE ORGAN-PIPE. 



The vibrations of the air reed of a sounding organ- 

 pipe may be shown, by having a small pipe made of 

 iron gas-pipe and blown by illuminating gas, which may 

 be lighted ; and when the pipe is sounding the reed will 

 be seen to swing backward and forward in front of the 

 embonchure. That it really vibrates may be seen by re- 

 flecting the light from a mirror upon a screen, and tilt- 

 ing the mirror, as is done in showing the manometric 

 flames. 



MACH'S EXPERIMENT. 



The movement of the air within a sounding organ- 

 pipe has been studied optically by Mach, a German 

 physicist. His method was to stretch a membrane 

 across the node of a pipe with glass sides, and in the 

 open end he ran a fine platinum wire to the membrane, 

 and thence out to be connected with a galvanic battery. 



