258 Mr. Willis on the Vowel Sounds, 



wind-chest to the portevent. To get rid of this, I fairly set the 

 end of the portevent into the lid of the bellows, as represented 

 in Fig. 14, so that the lower extremity T of the pipe, or vibrating 

 column, should be perfectly well defined. Now indeed the reed 

 became silent, when T'F' = 5.9, and spoke again at about 8, 

 leaving a ditFerence in length from the former experiment of 

 2.5 inches, so that there can be little doubt, but that the passage 

 efg is to be reckoned as part of the portevent, and perhaps 

 may serve to account for the anomalous results obtained by 

 M. Grenie. Pursuing this enquiry, by means of the longer tubes. 

 Figs. 15, and 16, I found as I expected, that these intervals of 

 silence, flattening, &c. occurred regularly, whenever the portevent 

 was made nearly equal to some odd multiple of the half-wave 

 of the reed*. There are faint indications of vowels in this 

 case. (See Note C). 



I shall conclude with a few experiments, which appear to 

 confirm the views already laid down. Take a piston MN, Fig. 8, 

 very nearly of the diameter of the tube ABCD, Fig. 6.t By 

 means of the slender handle 0, it may be made to slide up and 

 down the tube, as represented in Fig. 8. If this is done, the sound 

 of the reed goes on without interruption, putting on, but rather 

 less distinctly than before, the vowel qualities, in direct and 

 inverse order alternately, corresponding to the length of tube 

 BN, between the end of the piston and the mouth, whatever be 

 the length of PB : while, on the other hand, whenever the length 

 PM is made nearly equal to the whole wave of the reed, or some 

 multiple of it, the flattening and other phenomena take place. 



* As therefore there are certain lengths of portevent, which prevent the reed from 

 speaking, it is necessary to have the power of adjusting TVR, Fig. 6, to the reed made 

 use of: this is done by a sliding joint at V, which may be fixed to the required length 

 by a clamp, all this is omitted in the figure to avoid confusion. 



t Diameter of tube= 1.3 in., of piston = 1.25 in. 



