PIERCE. — A METHOD OF MEASURING THE INTENSITY OF SOUND. 395 



be thrown off the scale when a small organ-pipe was sounded almost 

 anywhere on the same floor of the building, even when the passage of 

 the sound from the pipe to the transmitter was through long corridors 

 and several partly closed doors. With the pipe at P and the trans- 

 mitter, without sound-collector, placed at 3 in the room shown in 

 Figure 7, a delicate Weston ammeter gave a whole scale deflection, 

 which corresponded to a current of 392 microamperes. With the use of 

 this ammeter instead of the galvanometer readings could be taken with 

 great rapidity and may be easily made self-recording. 



To test further the sensitiveness of the apparatus with the carbon 

 transmitter substituted for the magneto-telephone receiver, this trans- 

 mitter was supplied with long leads and placed outside the building. 

 An assistant was sent off across an open field. When the assistant 

 blew a small organ-pipe, C 6 , 1024, at a distance of 100 meters away, a 

 deflection of 5 mm. corresponding to a current of 3.06 X 10~ 8 amperes 

 was obtained. A locomotive whistle at a distance of perhaps a mile 

 gave 75 millimeters deflection. 



Jefferson Physical Laboratory, 



Harvard University, Cambridge, Mass. 

 December 27, 1907. 



