and on Reed Organ-Pipes. 255 



by different lengths of pipe. Its motion, taken alone, is well 

 known to be considerably nnder the dominion of the current 

 of air by which its pulsations are maintained*, and if a pipe 

 be attached to it, it will plainly be also subjected to the 

 periodic return of the secondary pulsations, by which we may 

 expect to find the time and mode of its oscillations affected. 

 We have seen, however, that when the pipe is about the length 

 of some odd multiple of the half wave, the secondary pulses are 

 united. Here it is then that we may look for the greatest 

 disturbance of the motion, and accordingly our experiments have 

 shewn us, that the pitch of the reed, and consequently its oscil- 

 lations, are only affected on approaching such lengths of the 

 attached pipe. At other lengths it would appear that their impulses 

 being separated, and falling in succession on the reed, are in- 

 capable of producing any sensible effect on its motion, although 

 they are able to qualify the tone by imparting to it the vowel 

 qualities. 



Now as the reed moves outwards, a rarefied pulse is gene- 

 rated, which travels to the extremity of the pipe, and returns 

 condensed; and supposing the pipe equal half a wave, the 

 beginning of this secondary pulse will just coincide with the 

 extremity of the first, so that as the reed returns, it is met by 

 this reflected pulse, which tends to check the extent of its excur- 

 sion, and, as it seems, to increase the time. The condensed pulse 

 now generated will, in like manner, present a new secondary 

 rarefied one, which will retard the reed during its outward motion, 

 and .so on. 



But as the length of the pipe was taken equal to half the 

 wave of the reed in '\t% free oscillations, it appears that the wave 

 now produced, since the note is flatter, will be of greater extent, 



* Biot, Physique II. 16Y. 



