Mechanism of the Larynx. 347 



outwards is less than the accelerating force at the same point in returning, 

 and the difference gives us a force to balance the loss from friction and 

 resistance, which will therefore keep the membrane in motion as long as 

 the current is kept up. 



A similar explanation will apply to the case of the reed of an organ pipe, 

 to the free reeds now so much in vogue, and to every other case in which 

 a vibratory motion is maintained by a current. For instance, let A BCD 

 Fig. 21, be a transverse section of the plate of a free reed, and let EF be 

 the two extreme positions of the vibrating tongue which passes through 

 the aperture BC of the plate, the dotted line being its position of rest. 

 When in the position F, the current indicated by the arrows rarities the 

 air above the tongue by the lateral communication of motion, which action 

 ceases the moment the plate gets to the level of BC, while a similar process 

 commences at the lower surface of the tongue, and ceases when it returns 

 to BC; affording in both cases a retarding force in going from BC less 

 than the accelerating force in returning to it, and therefore maintaining 

 the motion as long as the current is kept up. Here the tongue is first 

 started into motion by the upward pressure of the current; and if the 

 position of the tongue be not accurately adjusted, it is found that it will 

 either assume a position of rest a little above that which it takes when 

 no current acts upon it, or else will get very slowly into motion. 



I propose to enter more fully however into this subject hereafter. 



M. Biot* has attempted to explain the motion of an organ reed in a 

 way which would be perfectly satisfactory upon the hypothesis of perfect 

 elasticity and non-resistance of the air, but in no other case. Were his 



* Physique, t. II. pp. 166, 172. Precis elementaire, t. I. pp. 420, 431. Also Pouillet. 

 Physique, t. II. p. 180. 



M. Biot also adapted two lips of India rubber to a pipe connected with organ bellows, 

 and upon passing the current of air through them he obtained sounds. (Precis elementaire 

 de Physique, t. I. p. 4&>.) 



IV. IV. Part III. Y v 



