236 BELL SYSTEM TECHNICAL JOURNAL 



given a slow uniform rotation about its vertical axis. With the 

 film on the drum, the record thus had a helical form. In this way 

 records of the requisite length were obtained. 



The condenser transmitter was of the l\pe dexelopcd !)>■ E. C. 

 VVente, its characteristics combining with those of the amplifier and 

 oscillograph vibrator in such a way that the combined amplitude 

 response for the whole system was fairly uniform up to 5000 cycles, 

 while the phase lag was approximately a linear function of frequency 

 over the same range. This apparatus was therefore well adapted to 

 the production of faithful records of the vowel sounds. The photo- 

 graphic equipment permitted the use of a time scale as great as six 

 meters per second on the record (i.e. 2 inches = 0.01 sec.) 



Tr.\NSFORMATIOX of RECflRDS FOR .-\naI.VSIS* 



The oscillograms taken with the abo\e apparatus were line records; 

 in order to analyze these wave forms by the photo-mechanical method 

 outlined below, it was necessary to transform the line record into a 

 black profile. This was accomplished in the following steps: 



(1) A positive print of the wa\e form on the original record was 

 made on motion picture film. 



(2) The emulsion of the positi\e print was then cut through to 

 the base along the line of the wa\e by means of a stylus. 



(3) The entire strip was blackened (on the emulsion side) with 

 printer's ink. 



(4) The eniulsidii on one side of tjie wave was stri|i]ie<i Iroiii the 

 base, thus leaving the prolile. 



(5) The beginning and end were joined to form an endless belt. 



Pii(iiii-Mi;( iiANu Ai. .\nai.vsis ok TiiF Prki'arkd Rkcori>s^ 



The principle of the photo-mechanical analysis is as follows: The 

 motion of the strip past the image of an illuminated slit causes fluc- 

 tuations in a beam of transmitted light which in turn, produce volt- 

 age fluctuations in the circuit containing a selenium or photo-electric 

 cell. This \oltage is then analyzed by means of a tuned circuit, 

 an amjilifier and a rectifier. The frefiuenc>' of any component 

 selected in this manner is determined by the tuning frequency di\ided 

 by the ratio of speed transformation (analysis speed divided by the 

 original speed of recording). The measured amplitude of the selected 



* Phys. Rev. 23, 1924, p. 300 It is planned to i)ublish a more (ictailed descrip- 

 tion of this apparatus later. 



