EXPERIMENTAL PHONETICS. 



251 



An ideal method tor recordin<;- vibrations was devised by Rops in 

 1893. ideal inasmuch as it does not use any vibrating membrane or lever 

 or anything having inertia. A diagram is given in tig. 22 



It is based on the principle of photo- 

 graphing the effects of interf(>rences of 

 light waves. Kays from a luminous 

 source A pass through the lenses y y so 

 as to become parallel. They then pass 

 through a slit d and a hole in a dia- 

 phragm I. and they are focused by a 

 lens / (of 15 centimeters focal length) so 

 as to fall on a glass plate S^. The ray 

 divides into two, a^ and '/.,. and they run 

 ])arallel, the ra}' a^ passing through the 

 air while (/.. passes along a tube </ (15 

 centimeters in length), the ends of which 

 are closed by the glass plates h and //j. 

 A few centimeters from the tube there 

 is a resonator. /, into which the vowels 

 are sung, thus causing condensations and 

 rarefactions of the air. disturbing the 

 ray /( h^ while the rav passing through 

 the tube g is unaffected. The two rays 

 are again united by Sji they then pass 

 through an objective c and a lens z to a 

 slit in a screen so as to fall on sensitive 

 paper on the drum T. A diaphragm h 

 cuts off' secondary reflections. Thus 

 beautiful images are formed correspond- 

 ing to the vowels spoken or chanted into 

 the resonator. 



The invention of the tin-foil phono- 

 graph ])y Edison in 1877 and the improve- 

 ment of the instrument by the labors of 

 Edison, Graham Bell, and others in more 

 recent years has made it possible to in- 

 vestigate phonetic phenomena with the 

 aid of this instrument. In 1878 Fleem- 

 ing Jenkin and Pawing" devised a method 

 of recording curves from the imprints 

 on the tin-foil covering the drum of the phonograph, and these curves 

 were submitted to harmonic analysis. This was also attempted bv 



« Fleeming Jenkin and Ewine: On the Harmonic Analysis of certain Vowel Sounds 

 (Trans. Roy. Soc. Edin., vol. xxviii. ]>. 745). 



