486 THE BELL SYSTEM TECHNICAL JOURNAL, APRIL 1951 



phone Laboratories on the growing of large single crystals of three different 

 piezoelectric materials: ammonium dihydrogen phosphate (ADP); ethylene- 

 diamine tartrate (EDT); and quartz. Included are illustrations of some 

 basic principles observed in the growing of these crystals, descriptions of 

 improved apparatus for their growth, and pilot plant problems encountered 

 in conjunction with the commercial production of ADP and EDT. 



Sttidies of the Propagation Velocity of a Ferromagnetic Domain Boundary * 

 H. J. Williams,^ W. Shockley,^ and C. Kittel.^ References. Phys. Rev., 

 V. 80, pp. 1090-1094, Dec, 15, 1950. 



Abstract — This paper discusses the results and interpretation of measure- 

 ments of the propagation velocity of a ferromagnetic domain boundary in 

 the single crystal of silicon iron with a simple domain structure employed 

 previously by Williams and Shockley. The experiment is similar in prin- 

 ciple to the Sixtus-Tonks experiment, with the important difference that 

 in the present experiment the eddy current configuration is amenable to 

 exact mathematical calculation, thereby enabling a quantitative comparison 

 with observation. Experiments and analysis similar to those described in 

 paragraphs III and V have been carried out by K. H. Stewart and were re- 

 ported at the Grenoble Conference on Ferromagnetism and Antiferromag- 

 netism as were the principal results of this article. However, it appears 

 from Stewart's hysteresis loops unlikely that his specimen had as simple a 

 domain structure as that encountered in our experiments. 



Progress in Development of Test Oscillators for Crystal Units* L. 

 F. KoERNER.i I.R.E., Proc, v. 39, pp. 16-26, Jan., 1951. 



Abstract — Early crystal unit test oscillators as conceived some 20 years 

 ago were principally duplicates of the actual equipment in which the crystal 

 units were to be utilized, a practice which resulted in a large variety of 

 test circuits and procedures for testing. It is now recognized that a knowledge 

 of the equivalent electrical elements making up the crystal unit is essential 

 to the circuit engineer, and that the older conception of frequency and ac- 

 tivity, the latter being an attempt to express the quality of a crystal unit in 

 terms of a particular oscillator circuit, do not define adequately its charac- 

 teristics. The equivalent electrical circuit of the crystal unit contains essenti- 

 ally a resistance, an inductance, and 2 capacitances, which together with 

 frequency define the performance of the unit. Crystal units are available 

 in the frequency range from about 1,000 cycles to over 100 Mc. Their re- 

 sistance range may vary from less than 10 ohms to over 150,000 ohms, the 

 inductance from a few millihenries to nearly 100,000 henries and the capaci- 



* A reprint of this article may be obtained on request to the editor of the B. S. T. J. 

 iB.T. L. 



