Trouton — On the Control Supply-Pipes have on Ret 



133 



jiosition of the piston when the reed first sounded freely was about 

 one quarter of a wave length from the reed. 



With reeds of different pitch slightly different results were 

 obtained. When the note of the reed employed was low, the piston 

 in the control tube required to be much nearer to the definite posi- 

 tions, in order that the reed might sound, than for higher notes. 

 When a reed of moderate pitch (about 650) was used it was 

 observed to act as follows : — When the piston was in the whole 

 way, the control tube, of course, had no effect, but when drawn out 

 some little distance the reed commenced to sound a lower note than 

 when free. As the piston receded the note suddenly rose to nearly 

 that of the free reed, which it attained a little further at a point a 



3\ 



4 



5\ 

 4 



lh Distance 

 4 



little short of a quarter of the wave length from the reed. From 

 that on the note fell, until, when half a wave length from the last 

 place, it suddenly rose again, and, as before, when the piston was 

 slightly short of three quarters of the wave length, the reed sounded 

 freely, and so on in order to the end of the tube. The diagram is 

 intended to roughly represent this. The distance along the control 

 tube is here marked in quarter wave lengths, beginning at a point 

 a little outside the reed. The ordinates represent the number of 

 vibrations per second. When the piston was moved in the opposite 

 direction, as might be expected, the sudden fall in pitch occurred 



