256 Mr. Willis on the Vowel Sounds, 



so that the pipe may be lengthened to correspond to the new 

 value of the iialf wave. But this being done, the same reasoning 

 will sliew that the excursion of the reed should be still further 

 diminished in extent, and augmented in time; and in this way 

 we may go on increasing the length of the pipe, diminishing 

 the extent of the excursions, and flattening the note, till we 

 reach some point where it will be easier for the reed to oscillate 

 in the original mode, anil there it will of course return to that 

 mode of vibration. But the length of pipe at which this change 

 takes place, will manifestly depend upon the elasticity of the 

 reed, and the pressure of the current, and may therefore vary 

 with different reeds and pressures as we have found it to do. 



But we have seen that when the interval of the secondary 

 pulses is somewhat greater than that of an oscillation of the reed, 

 there is a slight tendency to accelerate the motion in diminishing 

 its extent. If this once takes place, a similar line of reasoning 

 will shew, that upon shortening the pipe to accommodate it to 

 the new wave, it must go on rising in pitch till it reaches some 

 point where it will be easier for it to vibrate in the other way. 



That the lengths of pipe producing all these alterations of 

 pitch are unfavorable to the reed's motion, is proved by the fact, 

 that with them a less weight of wind reduces the reed to silence, 

 although such less weight is quite sufficient to make the reed 

 speak freely with favorable lengths. It also appears by the same 

 test, that the lengths with which the sharpening takes place are 

 considerably more unfavorable to the reed's motion, than those 

 which flatten it. 



The fact of certain lengths of pipe being unfavorable to the 

 motion of the reed, naturally recalls the experiments of M. Grenie*. 

 This gentleman found, that with some notes of the scale, he 



* Biot, Physique, II. 173. 



