Abstracts of Bell System Technical Papers 



Not Appearing in the Bell System 



Technical Journal 



Photomechanical Wave Analyzer Applied to Inharmonic Analysis} 

 C. F. Sacia. This type of Fourier Analysis deals with wave-forms 

 which are not strictly periodic, since they are of finite duration and 

 of varying cyclic forms. Hence in a finite frequency range they have 

 an infinite number of infinitesimal components (shown by the Fourier 

 Integral) as contrasted with the finite number of finite components 

 at regular intervals (shown by the Fourier Series). 



This analyzer utilizes the continual repetition of the aperiodic 

 wave, deriving therefrom a periodic wave, the infinitesimal compo- 

 nents neutralizing except for frequencies which are integral mul- 

 tiples of the frecjuency of repetition; here the components build up 

 to finite magnitudes. The simple relation between these components 

 is seen from the corresponding Fourier Integral and Series identities 

 for the unrepeated and repeated waves respectively. By increasing 

 the period of repetition a new set of components can be similarly 

 derived. 



The wave form is represented as a black profile on a transparent 

 strip whose ends are joined to form an endless belt. Driven at con- 

 stant speed past a transverse illuminated slit, it generates light fluctu- 

 ations which are converted into electrical fluctuations by means of a 

 selenium cell. A tuned circuit, amplifier, rectifier and microammeter 

 are used to select and measure the components, while the frequencies 

 are determined by the speed of the strip, the frecjucncy of tuning, 

 and the time scale of the original wave form. 



"Demagnetization and Hysteresis Loops.'"- L. W. McKeehan and 

 P. P. CiOFFi. The fact that permalloy shows its maximum initial 

 permeability in the absence of external magnetic fields is used to 

 check the exact compensation of the earth's magnetic field or other 

 stray fields by measurement of the initial permeability of a strip or 

 wire of permalloy placed parallel to the field component to be com- 

 pensated. Increased accuracy is obtained by the use of somewhat 

 greater fields than those which approximately give the initial permea- 

 bility. The effect of demagnetization by an alternating current field 

 is sluflied with samples of the same sort, the apparent permeability 

 varying as the external field at the time of magnetization is \-aried. 

 The dissymmetry in hysteresis loops where the upper and lower limits 



' J. O. S., K. S. I., Vol. 9, pp. 487-494, 1924. 



» J. O. S., K. S. I., Vol. 9, pp. 479-485, 1924. 



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