Abstracts of Bell System Technical 



Papers Not Published in 



This Journal 



A New Telephone Carrier System for Medium-Haul Circuits. R. vS. 

 Caruthers S H. R. Huntley-, W. E. Kahl\ and L. Pederson^ 

 Elec. Eng., 70, pp. G92-G93, Aug. 1951. 



Low terminal costs and single-cable operation make this the first economically 

 practical carrier system for medium-haul telephone circuits. Performance is not 

 sacrificed for economy. 



A .15-Kw 500-Megacycle G rounded-Grid Tridode.* C. E. Fay^ D. A. 

 A. Hale', and R. J. KircherI. Proc. I.R.E., 39, pp. 800-803, July, 

 1951. 



Short-Cut Method Aids Figuring Exhaust and Collecting Systems. W. 

 H. Fogle^ Heating, Piping and Air Cond., 23, pp. 75-78, July, 1951. 



A simple, workable method of determining static losses in industrial exhaust 

 and coUecting systems is explained here by means of a sample problem and its 

 step-by-step solution. The method might be described as an "averaging out" 

 process, whereby all duct sizes and lengths are averaged out with the cfm and 

 velocity to give a total linear footage of the average duct size and an average 

 velocity. 



Arcing at Electrical Contacts on Closure. Part I. Dependence Upon 

 Surface Conditions and Circuit Parameters.* L. H. Germer'. Jl. Appl. 

 Phys. 22, pp. 955-964, July, 1951. 



In a low-voltage circuit the occurrence of an arc between approaching elec- 

 trodes is dependent upon the nature of the surfaces and upon the circuit induct- 

 ance. For carbon surfaces, or noble metal surfaces which have been "activated" 

 by operation in various organic vapors resulting in a carbonaceous layer, the 

 limiting circuit inductance is somewhat above 10~%, wliich is much higher 

 than the limiting inductance for clean noble metal surfaces. This activation by 

 organic vapors occurs for noble metals only and for certain vapors; for example, 

 benzene derivatives. In the case of silver and benzene vapor, it has been shown 

 that the activation is due to adsorption of benzene onto a greasy surface layer 

 and its decomposition there by the heat of subsequent closures. A metal surface, 

 which has been activated by organic vapor, remains active indefinitely if there 



* A reprint of this article may be obtained on request. 

 iBell Tel. Labs. 



A. T. &'t. Co 

 3W. E. Co. 



201 



