ABSTRACTS OF TECHNICAL ARTICLES 687 



with the high electromechanical coupling and the high Q's make it appear 

 probable that these crystals may have considerable use as a substitute for 

 quartz which is difficult to obtain in large sizes. These crystals are ethylene 

 diamine tartrate (CeHijNiOe) and dipotassium tartrate (K-jC4H.i06, |HcO). 

 Complete measurem.ents of the elastic, piezoelectric, and dielectric constants 

 of the dipotassium tartrate (DKT) crystal are given in this paper. The 

 crystal has 4 dielectric constants, 8 piezoelectric constants, and 13 elastic 

 constants. A discussion is given in the appendix of the method of measuring 

 these constants by the use of 18 properly oriented crystals. 



An Acoustic Constant of Enclosed Spaces Correlatable ivith Their Apparent 

 Liveness}^ J. P. Maxfip:ld and W. J. Albersheim. An acoustic constant 

 called liveness is derived, which constant is correlatable with the acoustic 

 properties of the enclosed space and with the distance between the sound 

 source and the listener. This constant represents the ratio of a time integral 

 of the energy density of the reverberant sound to the unintegrated energy 

 density of the direct sound. The validity of this constant is substantiated 

 by empirical data. Certain subjective effects of monaurally reproduced 

 sounds as a function of the liveness of its pick-up conditions are briefly 

 discussed. 



Directional Couplers}^ W. W. Mumford. The directional coupler is a 

 device which samples separately the direct and the reflected waves in a 

 transmission line. A simple theory of its operation is derived. Design data 

 and operating characteristics for a typical unit are presented. Several appli- 

 cations which utilize the directional coupler are discussed. 



Theory of the Beam-Type Traveling-Wave Tnhe}^ J. R. Pierce. The 

 small-signal theory of the beam traveling- wave tube has been worked out. 

 The equations predict three forward waves, one increasing and two attenu- 

 ated, and one backward wave which is little affected by the electron stream. 

 The waves are partly electromagnetic and partly disturbance in the electron 

 stream. The dependence of the wave propagation coefficients on voltage, 

 current, circuit loss, and the other properties of the transmission mode which 

 propagates energy and the^^cut-off transmission modes is given. Expres- 

 sions for gain and noise figure and an estimate of power output are given. 

 Appendix A gives an expression for the field in a uniform transmission system 

 due to impressed current (as, of an electron stream) in terms of the para- 

 meters of the transmission modes. Appendix B calculates the propagation 



^^ Jour. Aeons. Soc. Amer., January 1947. 

 i^Froc. I.R.E., February 1947. 

 18 Pw. I.R.E., February 1947. 



