TONE OF THE VOICE. . 469 



which is pierced, at its centre, "by a hole about the sixth of an inch 

 in diameter. Sometimes, it has the shape represented in the next 

 marginal figure. By placing this instrument between the teeth and 

 lips, and forcing air, with more or less strength, 

 through the two apertures, different sounds can be Fi s- 20 - 



produced. This is more certainly effected, by attach- 

 ing a porte-vent to the whistle, as A A, Fig. 200, 

 when it is capable of producing all the sounds com- 

 prised in an extent of from an octave and a half to 

 two octaves. M. Savart found, that, other things 

 being equal, the diameter of the apertures has an ap- A. 

 preciable influence on the acuteness or graveness of 

 the sounds, which are graver the larger the orifices. 

 The nature of the parietes of the instrument appeared, 

 also, to exert some effect on the number of oscillations, Scheme of a Bird . 

 and the quality of the sounds ; and if, in the hemispher- call. 

 ical whistle, Fig. 200, the plain plate was replaced 

 by a thin leaf of some extensible substance, as parchment, the sounds 

 issued more rapidly, and were usually more grave, full, and agreeable, 

 than when it was formed of a more solid substance. 



It is an opinion generally admitted, that the material, which com- 

 poses an organ-pipe, has no influence on the number of vibrations, 

 which the column of air, contained in it, is capable of executing. This 

 is true as regards long pipes ; but, according to M. Savart, it is not so 

 with short ; and the nature of the biseau 1 he conceives, may have a 

 glfeat influence, even on the sound of long pipes. For instance, if we 

 .substitute, for the stiff lamina, which forms the biseau of an organ 

 ,})ipe two feet long and two inches on the side, a lamina, formed of 

 some elastic substance, as skin or parchment, so arranged as to admit 

 of being stretched at pleasure by gradually increasing the tension 

 of the membrane, at the same time that we increase the velocity of 

 the current of air, the tone may be made to vary^a fourth, and even 

 a fifth. In shorter tubes, the much greater influence of the velocity of 

 the current of air being united to that of the tension of the biseau, the 

 result is still more evident. Thus, the sound of a cubical tube may be 

 easily lowered an octave, when the parietes of the biseau are suscepti- 

 ble of different degrees of tension; but when all the parietes of a short 

 pipe are of a nature to enter into vibration along with the air they 

 contain, and when their degree of tension can be, moreover, varied, 

 they have such an influence on the number of vibrations, that the 

 sound may be greatly modified. Short tubes, open at both extremities, 

 and formed of elastic parietes, are also susceptible of producing a great 

 variety of sounds, even when they are only partly membranous; and the 

 quality of the sound of membranous tubes is said to be somewhat pecu- 

 liar, partaking of that of the flute, and of the free reed. Again, in 

 order that a mass of air shall enter into vibration, a sound must be 

 produced in some part of it. In an organ pipe, for example, a sound 



1 The biseau or languette is the diaphragm placed between the tody of an organ pipe and 

 its foot. 



