1879.] 



Studies in Acoustics. 



363 



Figs. 7 and 7a show reproductions of the vowel 0, sung at 

 different pitches, as determined by Messrs. Fleeming Jenkin and 

 Ewing. 



14. [It is worth remarking parenthetically, that one interesting 

 fact arising from the operation of this machine, was that curves could 

 be so constructed as to give a stereoscopic effect. One curve was 

 drawn simple, and the other, drawn in the same line — at the proper 

 distance from it to fit a stereoscope — was made compound, by the 

 addition of a partial of low amplitude. The result of the combination 

 by the eye in a stereoscope of these two curves, was to produce a 

 perspective effect. By this means curves have been drawn which in- 

 terlace amongst each other, giving stereoscopic effects in a manner 

 which is unique and interesting. This has no bearing whatever on 

 the investigation, and is only adduced as a scientific toy arising out of 

 the enquiry.] 



15. Having thus studied the formation of vowel sounds, and having a 

 means to reproduce the compound curves which graphically represent 

 the motions which the air particles assume under their influence, the 

 authors determined to try to reproduce these vowels by superimposing 

 partials on to a given prime. 



Since vowels are produced by a prime and its upper partials, and as 

 the upper partials diminish so rapidly in amplitude, the idea arose that 

 these vowels might be reproduced by sounding a prime and one of its 

 partials alone. This was done by means of an electro-magnet E, fig. 8, 

 vibrating an armature (A) with a moveable spring (S) attached to it 

 in such a way that the vibrations of the armature could produce a 

 given prime, while the vibrations of the spring, by varying its length, 

 could also be adjusted to any particular partial. 



16. The result was to roughly reproduce the principal vowel sounds, 

 but the effect not being by any means perfect (due to the absence of 

 the other upper partials), a machine was made on the principle of the 

 synthetic curve machine, which w r ould, instead of drawing curves on 

 paper, reproduce eight partials by transferring the vibrations of the 

 intermediate wheels to a vibrating diaphragm. This machine consists 

 of eight wheels fixed on the same axis, the periphery of the wheels 

 being cut into teeth of such a number as to represent the eight partials. 

 Each tooth is a simple harmonic curve, and each wheel represents one 

 partial. The axis can be rotated by a crank at any given velocity. By 

 depressing a key a spring can be brought into contact with the edge 

 of each wheel, and be thus vibrated. The vibrations of these springs 

 are transferred by thin cords and intermediate linking to a diaphragm 

 of ebonite. Each spring can be depressed separately or simultaneously 

 with others, and the disk will vibrate to the resultant effect of all the 

 vibrations. Thus, notes and chords can be sounded. 



17. Here again, though the vowels were fairly reproduced, some- 



