Trouton — On the Control Supply-Pipes have on Reeds. 135 



tance of one quarter of a wave length from the reed. Now when 

 the piston was placed at one quarter of a wave length along the 

 tube the reed would not sound, but when it came near a half 

 wave length the reed sounded freely, as it had done at one quarter 

 of a wave length in the previous experiment, when the control tube 

 was inserted at the reed, thus showing that when the reed sounded 

 freely the point at one quarter of a wave length from the reed was 

 a node, and that the reed must be at, or at least nearly at, a loop, 

 as was before determined. 



Experiments were made with a beating reed (the one used was 

 a bassoon reed) to see if it were at a node under similar circum- 

 stances, the theory perhaps referring more especially to them ; but 

 as far as the experiments went it appeared always to be at least as 

 near to a loop as a node, generally much nearer. However, these 

 experiments were open to considerable uncertainty as to their 

 meaning, as Professor FitzGerald pointed out, for in this case it 

 is probably insufficient to consider only the vibrations taking place 

 in one dimension. From these experiments it is obvious how a 

 long supply tube often can prevent a reed from sounding freely. 

 For the tube must be of such a length as to break up into the 

 right number of vibrating segments, so as to agree in period with 

 what the reed can sound, and also so as to have the reed near to 

 a loop. It is easy to see that with a long tube of given length 

 these conditions are not so likely to be fulfilled in the case of a 

 reed of low pitch as in that of one of higher pitch ; for when the 

 length of the tube is many times that of the half wave length — 

 even if there should be the maximum discrepancy between the 

 nearest number of half wave lengths and the tube — a small per- 

 centage lengthening in the half wave length, to which a reed can 

 always alter itself, will allow of the reed sounding, the note, of 

 course, being slightly lower. The corresponding change in pitch 

 required in the case of a low-pitched reed might easily be 

 so great that the reed could not possibly sound a note so much 

 lower than its own. Besides this, in the case of low notes, even 

 when the pitch is such as to admit of the necessary agreement 

 between the wave length and the tube, the tendency of long narrow 

 tubes when sounding low notes to break up into harmonics makes 

 it often almost impossible to get the reed to sound. 



