408 



BELL SYSTEM TECHNICAL JOURNAL 



PAPER 

 ROLL 



SHADOW OF STRING 

 CLUTCH ROLL. 

 CYLINDRICAL LENS. 

 VIEWING SCREEN -J^ 



CONDENSING 

 LENS 

 OCCULTING-^ \ 

 TIMING , " " 

 WHEEL /| 



LAMP 



STORAGE TANK 



Fig. 8 — Diagrammatic arrangement of Curtis oscillograph. 



maximum component. When the conditions are such that a current 

 can be steadily maintained, the analysis can be made much more 

 conveniently and generally over a wider range of amplitudes by means 

 of one of a number of recently developed types of current analyzers. 

 These analyzers, although the mode of operation may differ in the 

 various types that are available, have the common characteristic that 

 they transmit only a narrow band of frequencies with the position of the 

 band adjustable along the frequency scale. For analyzing a current 

 wave the mid-frequency of the transmission band is shifted along the 

 whole frequency range and the magnitude of the current in each 

 frequency region is recorded or noted on a meter. This type of 

 analyzer may also be used to get a statistical distribution of the power 

 with respect to frequency when the sound is not periodic, as in certain 

 kinds of noise. 



High-Speed A nalyzers 

 For the rather detailed study of sounds whose wave form varies with 

 time, such as those of music or speech, an instrument is needed which 



