ABSTRACTS OF TECHNICAL ARTICLES 175 



Piezoelectric Frequency Control.^ F. R. Lack. This paper discusses 

 the use made of the piezoelectric effect in designing sub-standard time- 

 keepers and frequency generators. The nature of the piezoelectric 

 effect is outlined and mention is made of the various classes of crystals 

 in which it is found. The technic of setting up, electrically, various 

 types of mechanical vibrations in piezoelectric crystals is described 

 together with methods of obtaining very high frequencies. Other 

 applications of the piezoelectric effect, such as to loud speakers, sub- 

 marine signaling, etc., are briefly reviewed. 



Reverberation Measurements in Auditoriums.'^ G. T. Stanton, F. C. 

 ScHMiD and W. J. Brown, Jr. This paper presents some of the 

 problems encountered in attempts to measure the reverberation time 

 in auditoriums, and indicates certain procedures found helpful in their 

 solution. In addition, comparison is offered between results obtained 

 with two step-by-step methods and a continuous decay. 



6 Jour. S. M. P. E., October, 1934. 



' Jour. Acous. Sac. Am., October, 1934. 



