ABSTRACTS OF TECHNICAL ARTICLES 683 



cent nickel), tension (a) decreases resistivity, and magnetic field (H) in-" 

 creases it. Domain theory predicts the ratio a/H at which the resistivity 

 is equal to that of the unmagnetized specimen, and the theory is accurately 

 confirmed. Measurements are made in transverse as well as longitudinal 

 magnetic fields, and the difference between the resistances so measured is 

 shown to be independent of the distribution of domains in the unmagnetized 

 state; the erratic results reported in the literature are thus explained and 

 avoided. When magnetostriction is positive, the limiting changes of resis- 

 tivity with field and tension are sometimes found to be different; this is 

 shown to be caused by the variation of magnetostriction with crystallo- 

 graphic direction. 



A Wide-Titning-Range Microwave Oscillaior Tube.* John W. Clark and 

 Arthur L. Samuel. This paper describes a reflex-type velocity- variation 

 oscillator tube with a wide tuning range in the microwave band. The tube 

 will oscillate from 20C0 to 13,000 megacycles, but practical tuning considera- 

 tions limit the band in any one circuit to a two-to-one frequency range. 

 The problems involved in the design and a description of the various elements 

 are given. 



Accelerated Ozone Weathering Test for Rubber} James Crabtree and 

 A. R. Kemp. Light-energized oxidation and cracking by atmospheric ozone 

 are the agencies chiefly responsible for the deterioration of rubber outdoors. 

 Since these processes are separate and distinct, it is proposed to distinguish 

 between them in the evaluation of rubber for resistance to weathering. An 

 accelerated test for susceptibility to atmospheric ozone cracking is discussed. 

 Apparatus for conducting the test and for measurement of ozone in minute 

 concentration is described in detail. 



Measurements in Communications.^ N. B. Fowler. For convenient 

 reference, some of the more common measurement units and scales used in 

 communication engineering are presented in tabular form together with sup- 

 plementary explanatory text. Included in the table, which also indicates 

 the limitations involved, are quantities used in measuring power, volume, 

 circuit noise, sound, light, radio fields, crosstalk coupling, and certain other 

 transmission concepts. 



An Improved 200-Mil Push-Pull Density Modulator.'' J. G. Frayne, 

 T. B. Cunningham and V. Pagliarulo. A completely new variable- 



'' Proc. I.R.E. and Waves and Electrons, January 1947. 



^ Indus. & Engg. Cliemistry. .inalytical Edition, December 1946. 



^ Electrical Engineering, February 1947. 



^ Jour. S.M.P.E., December 1946. 



