Abstracts of Technical Articles from Bell System Sources 



Directional Ferromagnetic Properties of Metals} R. M. Bozorth. 

 This is a review of the magnetic properties of single crystals of iron, 

 cobalt and nickel and their alloys with each other. After a general 

 introduction and a description of recently developed technique some 

 new results are described which show for the first time that such 

 crystals are anisotropic in low as well as in high fields. The amount of 

 anisotropy is expressed usually by one "anisotropy constant" but 

 sometimes a second constant is necessary. These constants vary with 

 composition and temperature and their values are shown in tables and 

 curves. When the constants are small the material is especially 

 sensitive to strain and heat-treatment; this condition applies to some 

 of the iron-nickel alloys (permalloys). Small amounts of impurities 

 afifect the magnetic properties in low fields. By careful purification 

 and heat-treatment several crystals have been made which have 

 permeabilities of over 1,000,000. 



Use of Negative Regeneration in Radio Receivers} C. B. Fisher. 

 This paper gives a brief and simple explanation of gain stabilization 

 which can be secured by employment of the feedback property of an 

 amplifier. 



Electron Diffraction Studies of Cuprous Oxide} L. H. Germer. 

 Etched surfaces of single crystals of cuprous oxide produce electron 

 diffraction patterns consisting of spots and Kikuchi lines. In some 

 cases lines are observed corresponding to all of the most widely spaced 

 planes of copper atoms which are so situated as to be able to give 

 reflections on the photographic plate. An example is given, however, 

 of a diffraction pattern from which lines due to the most widely spaced 

 plane of atoms (111), are missing when this plane lies parallel to the 

 primary beam direction; the lines appear when the crystal is rotated 

 to destroy this parallelism. The existence of Kikuchi line patterns 

 indicates that the surfaces of etched cuprous oxide single crystals are 

 relatively smooth. When spot patterns also appear they show anoma- 

 lies which seem attributable to refraction, thus confirming the con- 

 clusion regarding smoothness. An example is given of an array of 



1 Jour, of Applied Physics, September 1937. 

 * R. M. A. Engineer, November 1937. 

 ^ Phys. Rev., November 1, 1937. 



184 



