PIERCE. — A METHOD OF MEASURING THE INTENSITY OF SOUND. 389 



the room (1, Figure 7), where a small track 10 cm. wide and 2 meters 

 long was run out perpendicularly from the wall. The telephone was 

 placed on this track with the opening of the sound collector toward the 

 wall, and readings of the galvanometer were taken with the telephone 

 at various distances from the wall. The results obtained are plotted in 

 Curve 4 of Figure 8. The abscissae of this curve are the distances in 

 centimeters from the wall measured to the opening of the sound col- 



Figure 7. — Diagram of large lecture room. P is the position of the source 

 of sound ; 1, 2, and 3, positions of the receiver. 



lector ; the ordinates are the corresponding values of the current ob- 

 tained in the galvanometer when the organ-pipe was sounded. The 

 first reading, .73 X 10"'' amperes, was obtained with the opening of the 

 sound collector of the telephone jammed tight against the brick wall. 

 On withdrawing the receiver from the wall by stages of 5 cm., while 

 keeping the opening of the sound collector always toward the wall, the 

 succeeding values of the curve were obtained, showing the occurrence 

 in this part of the room of very decided maxima and minima of 



