174 Mr. E. F. Relf on the Sound emitted by 



eddies visible, it could at once be seen that the paper was 

 actually swinging with the same period as the eddies. 



Fig. l. 



Paper /ncf/cator. 



Cy/tncfen 



Experiments were next made upon fine wires moving 

 "in air. The wires were mounted between two cross-pieces 

 attached to an extension of: the shaft of a small electric 

 motor, so that when the motor was running, the wire de- 

 scribed a circular path of known radius (see fig. 2). The 



Fig. 2. 



Exper/men taf 

 W/re 



velocity of the wire was obtained from a determination of 

 the speed of rotation of the motor, a small correction being 

 applied for the swirl velocity produced by the cross-pieces 

 and wire. This swirl velocity was measured directly by 

 means of a small vane anemometer mounted as near as 

 possible to the track of the rotating wire. The notes heard 



