120 BELL SYSTEM TECHNICAL JOURNAL 



the conversion tables for translating from any system to any other 

 system show the essential equivalence of all five systems. It is 

 recommended that but one system be legalized and used generally in 

 place of the five systems, and that this universal system be the coherent 

 meter-kilogram-second-ohm or definitive system. It is further rec- 

 ommended that the international ohm be used in this system. This 

 unit is the one actually used in exploring the physical world because 

 laboratory resistances for physics and test room resistances for 

 engineering have been so calibrated. Of far greater importance is 

 the fact that by retaining the international ohm it will be simpler, and 

 completely feasible, to eliminate what Heaviside called "that un- 

 mitigated nuisance, the 47r factor of the present B.A. units" from our 

 preferred system of units. 



A Compensated Thermionic Electrometer."^ K. G. Compton and H. 

 E. Haring. a compensated single tube electrometer is described and 

 the principles of its operation discussed. This apparatus has been 

 found to compare favorably with "balanced tube" circuits both as 

 regards stability and sensitivity and to be superior in many respects 

 to the quadrant electrometers which usually have been used for the 

 measurement of small currents, high resistance, or of voltage in 

 circuits of high resistance and in those cases where only an infinitesimal 

 current may be drawn from the source of the electromotive force. 

 For most measurements the degree of compensation afforded has 

 been found to be sufficient to make possible the use of dry cells or 

 even properly controlled rectified alternating current as a power 

 source. 



Combined Reverberation Time of Electrically Coupled Rooms.^ A. P. 

 Hill. The importance of controlling the reverberation time of 

 auditoriums, music rooms, etc., is well recognized, and curves showing 

 the optimum reverberation times for buildings of different volumes 

 have been drawn and have attained general acceptance. In the 

 recording and reproduction of sound for talking motion pictures, 

 however, the reverberation problem is somewhat more complex than 

 is the case for rooms in which sound is originally produced, due to 

 the fact that there are three factors to deal with : first, the reverberation 

 time of the space in which the sound is recorded; second, that of the 

 space in which it is reproduced; third, the resultant reverberation 

 time produced by electrically coupling these two spaces together. 

 This is, of course, done in actual practice. This paper deals with the 



2 Electrochemical Society Preprint 62-17. 

 2 Jour. Acous. Soc. Amer., July, 1932. 



