Davis — Locating Nodes and Loops of Sound, etc. 263 



Art. XXVIII. — On a Method of Locating Nodes and Loops 

 of Sound in the Open Air with Applications ; by Bergen 

 Davis, Ph.D. 



The experiments and determinations given in this article 

 constitute an application of a new phenomenon recently 

 described by the writer in this Journal.* It is now my wish 

 to point out how the device previously described can be used 

 to locate nodes and loops of sound waves outside of organ- 

 pipes, and in general how the mechanical effects produced by 

 sound waves, at a distance from this source, can be studied. 



It having' been found that a small hollow cylinder which is 

 closed at one end, will move across a stationary sound-wave in 

 a direction perpendicular to the stream-lines, a small mill-like 

 arrangement was constructed by placing four hollow cylinders 

 on the ends of card-board arms, in such a manner that the 

 closed ends pointed 1 in the same angular direction. This mill 

 was provided with a glass pivot at its center, and was supported 

 on the point of a fine needle. 



The cylinders were made from 

 No. 00 gelatine capsules, and 

 were each l-7 cm long and -79 cm 

 in diameter. This system was 

 mounted in the mouth of a res- 

 onator, with the plane of the 

 system parallel to the mouth, 

 and hence perpendicular to the 

 direction of vibration. The 

 aperture of the resonator, with 

 the mill in place, is shown in 

 figure 1. The resonator was in 

 unison with an organ-pipe of 

 considerable power, and when 

 the pipe was blown the mill 

 was found to rotate with a 



high velocity, and the 'rate of rotation was different for differ- 

 ent positions in the room. By carrying the resonator around 

 a large room, the positions of the nodes and loops could be 

 located with considerable accuracy. 



The resonator containing the mill was next carried to another 

 large room, on the floor above that where the pipe was located : 

 there was no opening in the floor or ceiling between the rooms, 

 and the doors of both rooms were tightly closed, but in spite 

 of this, the mill was observed to rotate as before, but not so 

 rapidly. Nodes and loops could be located here also. 



* Bergen Davis, this Journal, Sept., 1901, p. 185. 



