ARTICLES BY BELL SYSTEM AUTHORS 477 



the solutions to problems may derive from previous experience, from empiri- 

 cal investigation, or from fundamental research. 



Illustrative examples are given to demonstrate the complementary roles 

 of engineering and research in correlating the properties of metals with 

 their structure, and their structure with their history of fabrication. 



Carrier Telephone on Rural Power Lines. J. L. Simon.'* Elec. Light & Power, 

 v. 28, pp. 92, 137, Oct., 1950. 



Abstract — A pictorial and diagrammatic treatment of the problems in- 

 volved in transmitting carrier telephone currents over existing rural power 

 lines. 



Weathering Studies on Polyethylene.^ V. T. Wallder,^ W. J. Clark,^ 

 J. B. De Coste,^ and J. B. Howard.^ References. Ind. & Engg. Chem., v. 

 42, pp. 2320-2325, Nov., 1950. 



Abstract — Polyethylene has been used for a number of years as a dielectric 

 material but only recently has it been considered as a mechanical protection 

 for wires and cables intended for direct exposure to the weather. Data are 

 presented on the results of a 10-year program on the effects of weather on 

 polyethylene. An accelerated test, which for the materials tested shows good 

 correlation with natural aging, is described and used to evaluate the aging 

 characteristics of compounds of polyethylene containing carbon black. 

 Data are given showing effects on aging of different types of carbon blacks 

 such as furnace and channel blacks, effects of carbon black concentration 

 on aging, the necessity for efficient dispersion of the carbon black in the 

 polyethylene, and the relation between aging and carbon-black particle size. 

 Age resistance of polyethylene is shown to increase as the average molecular 

 weight of the polymer is increased. These data indicate that channel grades 

 of carbon black which have a particle diameter of about 25 m/i or less when 

 well dispersed in an appropriate polyethylene at concentrations of 1 to 2% 

 can produce compositions having a natural outdoor life expectancy suffi- 

 ciently long to be considered for most outdoor applications in the wire and 

 cable field. 



Why Standardize Thicknesses of Thin Flat Metals. I. V. Williams.^ Stand- 

 ardization, V. 21, pp. 260-261, 272, Oct., 1950. 



Abstract — Before considering the methods of standardizing thicknesses of 

 metals, let us first consider why there should be any demand or need for such 

 standards. Some very strong arguments can be advanced in favor of such 

 practice, and the benefits which are derived therefrom should favor pro- 

 ducers, warehousemen, and consumers. 



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

 1 B. T. L. 



* S. W. Bell 



