220 



BELL SYSTEM TECHNICAL JUl'RXAL 



velocity in the glottis 7i corresponds to the plate current. In the 

 vacuum tube this plate current is modulated by varying charge, q-i, 

 on the grid. In the larynx the glottis air velocity is modulated by 

 varying displacement, q2, of the vocal cords. The charge on the 

 plate (again neglecting internal capacities except the grid-filament) 

 causes no effect on the grid mesh and in the larynx the position of 

 any element of glottis air has no effect on the vocal cords. The uni- 

 lateral mutual impedance, K,,, is the same in both. 



The analogy breaks down at the point where the " feed back " part 

 of the mechanisms is compared. The " feed back" is the bilateral 

 part of the mutual impedance between the two meshes. In the 

 vacuum tube circuit this is p-M, the mutual of the transformer, while 

 in the larynx it is pG, the " gyrostatic " mutual. The latter is a type 

 of element which does not occur in electrical circuits, arising as it 



^im(y^ 



mw 



^^AAJW — I 



^im^ 



■^ww 



a b 



Fig. 5 — Tuned Grid and Wind Reed Circuits. 



does from a variation of a mass or inductance with a displacement. 

 Inductance, being a function purely of the geometry of a circuit, 

 can only vary with mechanical displacement and not with electrical 

 displacement or charge. The gyrostatic mutual is common in the 

 mechanics of rotating bodies whence it derives its name. It is also 

 the mutual in an electromagnetic telephone receiver or relay be- 

 tween the electrical circuit and the armature or diaphragm. 



In order to fix the rather useful concept of the analogy in mind. 

 Fig. 5 is added showing the schematic circuit of the vacuum tube 

 (5a) and a circuit diagram (5b), which represents determinant (31) 

 the characteristic formulation of the dynamics of the larynx. Fig. 5b 

 is represented by the conventions of an electrical circuit, except for 

 the element G for which a different convention is necessary. The 

 one taken here is that of a resistance enclosed in a rectangle. From 

 (31) it will be seen to be similar to a resistance in its association with 

 frequency p but different from resistance in that it occurs non-sym- 

 metrically in sign in the determinant. It does not involve dissipation. 



