Abstracts of Technical Articles by Bell System Authors 



Dimensional Stability of Plastics} Robert Burns. Because of inherent 

 insulating properties, rigid plastics play an important part in the design and 

 manufacture of precision electrical apparatus. Almost invariably, practical 

 design considerations require that the plastics have reasonable structural 

 possibilities since it is rarely practicable to disassociate completely electrical 

 and structural functions. 



This paper discusses one of the important factors in the successful use of 

 plastics in precision devices, namely, dimensional stability. Since plastics 

 are organic compounds, one must be prepared to accept a degree of insta- 

 bility not usually encountered in metals. The measurement of this property 

 is therefore of prime importance to the user of plastics since the data provide 

 a basis for design adjustment which frequently is the difference between 

 failure and success. 



The various t^^pes of dimensional change are reviewed. Data illustrating 

 the separate effects of humidity, drying, and cycling procedures are sub- 

 mitted. The influence of fabricating processes such as compression or 

 injection molding, and sheeting, is included. 



Some Numerical Methods for Locating Roots of Polynomials.^ Thornton 

 C. Fry. It is the purpose of this paper to discuss the location of the roots 

 of polynomials of high degree, with particular reference to the case of com- 

 plex roots. This is a problem with which the Laboratories has been much 

 concerned in recent years because of the fact that the problem arises rather 

 frequently in the design of electrical networks. Attention is not given to 

 strictly theoretical methods, such as the exact solution by elliptic or auto- 

 morphic functions: nor to the development of roots in series or in continued 

 fractions, though such methods exist and one at least — development of the 

 coefl&cients of a quadratic factor — is of great value in improving the accuracy 

 of roots once they are known with reasonable approximation. 



Instead, the paper deals with just two categories of solutions: one, the 

 solution of the equations by a succession of rational operations, having for 

 their purpose the dispersion of the roots; the other, a method depending on 

 Cauchy's theorem regarding the number of roots within a closed contour. 



Thermistor Technics.^ J. C. Johnson. This paper is confined to a study 

 of how the three basic types of thermistors, namely, externally-heated or 

 ambient temperature type, the directly-heated type, and also the indirectly- 



^A.S.T.M. Bulletin, May 1945. 



^Quarterly Applied Matltematics, July 1945. 



' Electronic Industries, August 1945. 



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