474 THE BELL SYSTEM TECHNICAL JOURNAL, APRIL 1951 



or imperfections are independent of the uniform field and are given by the 

 usual expressions derived for zero field. This justifies the procedure of treat- 

 ing acceleration by the field and scattering as independent processes. 



Conductivity Measurements at Microwave Frequencies * A. C. Beck^ and 

 R. W. Dawson.J LR.E., Proc, v. 38, pp. 1181-1189, Oct., 1950. 



Abstract — Because of the skin effect, the surface condition of conductors 

 becomes very important in determining attenuation at microwave fre- 

 quencies. This has been investigated by measuring small wire samples at a 

 frequency of about 9,000 megacycles. A sample of the wire to be measured 

 is inserted in a metal tube to form the center conductor of an open-ended 

 coaxial line. The ratio of the peak frequency to the half-power bandwidth of 

 this coaxial-line resonator, measured with the aid of an oscillographic display 

 of its amplitude-versus-frequency characteristic, gives its loaded Q. The 

 amplitude characteristic of the frequency-modulated signal generator, on 

 which a wavemeter marker appears, is viewed simultaneously and used as a 

 reference. By correcting the result to obtain the unloaded Q of the center 

 conductor alone, the effective conductivity of the sample is obtained. 



Results of measurements on a number of samples of different conductors 

 having various surface conditions, treatments, and platings are given. 

 These results are of value in the design of microwave components of all 

 types where loss is a factor of importance. 



Propagation of UHF and SHF Waves Beyond the Horizon. K. Bullington.^ 

 Letter to the editor. LR.E., Proc, v. 38, pp. 1221-1222, Oct., 1950. 



Simple Torsion Pendulum for Measuring Internal Friction. M. E. Fine.^ 

 Jl. Metals, V. 188, sec. 1, p. 1322, Nov., 1950. 



Experiments on the Initiation of Electric Arcs* F. E. Haworth.^ Phys. 

 Rev., V. 80, pp. 223-226, Oct. 15, 1950. 



Abstract — Arcs have been struck in vacuum between widely spaced elec- 

 trodes by positive ion charging of an insulating film on the cathode, at sepa- 

 rations from 0.5 to 5 mm and at potentials from 34 to 2000 volts. The arc 

 current must be allowed to grow initially at the rate of at least 10^ amp./sec. 

 for the arc to occur. These experiments constitute a test of one of the funda- 

 mental steps postulated to account for the initiation of an arc between elec- 

 trodes coming together at low voltages. 



Mobilities of Molecular and Atomic Rare Gas Ions in the Parent Gases: 

 Helium, Neon, and Argon. J. A. Hornbeck.^ Letter to the editor. Phys. 

 Rev., v. 80, pp. 297-298, Oct. 15, 1950. 



Bell Telephone Laboratories — A n Example of an Institute of Creative Tech- 



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

 »B.T.L. 



