ABSTRACTS OF TFXIINICAL ARTICLES 191 



their use in ordinary photometric measurements, in which no pro- 

 nounced color differences are faced. Our study does not concern 

 itself with certain problems of sorting and selection, commonly spoken 

 of as "color" measurement, in which the nature of the colors concerned 

 and their range of deviation from certain standards are known in 

 advance, thereby greatly simplifying the problem. 



A Moving Coil Microphone for High Quality Sound Reproduction^ 

 V\\ C. Jones and L. W. Giles. A microphone is described in this 

 paper which retains all of the inherent advantages of the moving-coil 

 type of structure but unlike the earlier forms of this microphone 

 responds uniformly to a wide range of frequencies. It is more efficient 

 than the conventional form of condenser microphone and its trans- 

 mission characteristics are unaffected by the changes in temperature, 

 humidity and barometric pressure encountered in its use. Unlike the 

 condenser microphone the moving-coil microphone may be set up at 

 a distance from the associated amplifier and efficient operation ob- 

 tained. Owing to its higher efficiency and lower impedance it is less 

 subject to interference from nearby circuits. It is of rugged con- 

 struction and when used in exposed positions is less subject to wind 

 noise. 



The Shot Effect in Photoelectric Currents}^ B. A. Kingsbury. 

 The shot effect, as it occurs in a photoelectric current, has been used 

 to secure an evaluation of the electron charge. A new and original 

 method of amplifier calibration, which involved the use of a modulated 

 light beam, simplified the measurements and the computation of the 

 result. In the absence of space charge, the experimental value of the 

 electron charge w^as 1.61 X 10~^^ coulombs for a thermionic current, 

 and about 25 per cent greater for a photoelectric current. It was 

 found that the shot effect is enormously increased in photoelectric 

 currents which are amplified by collision ionization. Statistical 

 variations which might be expected to occur in a beam of radiant 

 energy could not be detected, since, within the limits of experimental 

 accuracy, the shot effect in photoelectric currents was found to be 

 independent of the frequency of the light producing electron emission. 



Some Acoustical Problems of Sound Picture Engineering}^ VV. A. 

 MacNair. The purpose of this paper is to point out that many 

 advances in acoustical engineering have been necessary in order to 

 understand and control adequately the conditions under which modern 



^"^ Projection Engineering, October, 1931. 

 ^^Phvs. Rev., October 15, 1931. 

 ^^Proc. I. R. £., September, 1931. 



