ABSTRACTS OF TECHNICAL ARTICLES 1247 



phone calls between the various communities in and around the city. Step- 

 by-step tandem equipment was employed and, as the volume of calls grew, 

 the trunk capacity was increased by installing additional switching equip- 

 ment. In 1946 it became evident that the abnormal rate of growth required 

 additions substantially beyond the practical size limit of the step-by-step 

 tandem unit. To solve the resulting problem, it became necessary to reor- 

 ganize the tandem trunking system and select a multiunit tandem switch- 

 ing plan. It also provided an opportunity to consider the application of the 

 more recently developed crossbar tandem switching system. This paper 

 reviews the factors affecting the general problem of interexchange trunking 

 which have led to the development of the present tandem network in the 

 Los Angeles metropolitan area. It describes the major elements of a system 

 which now employs a total of five tandem switching units, three of which 

 are crossbar tandem offices. 



p-n Junction Rectifier and Photo-cell. W. J. Pietenpol^ Letter to the 

 editor. Phys. Rev., v. 82, pp. 120-121, Apr. 1, 1951. 



Formulas for the Determination of Residual Stress in Wires by the Layer 

 Removal Method.* W. T. Read, Jr.^. //. Applied Phys., v. 22, pp. 415-416, 

 Apr., 1951. 



Abstract — The distribution of residual axial stress in a beam or wire of 

 circular cross section is derived as a function of the moment required to 

 straighten the wire after removal of successive layers of material. Applica- 

 tion of the formulas involves two graphical differentiations and integra- 

 tions of experimental curves. 



' Observation of Magnetic Domains by the Kerr Effect. H. J. Williams^ 

 F. G. Foster!, and E. A. Wood^. Letter to the editor. Phys. Rev., v. 82, 

 pp. 119-120, Apr. 1,1951. 



Particle Size in Suspension Polymerization.* F. H. Winslow^ and W. 

 Matreyek^ Bibliography. Ind. & Engg. Chem., v. 43, pp. 1108-1112, 

 May, 1951. 



Abstract — Control of size and geometrical form of densely cross-linked 

 hydrocarbon polymers yields fluid spherical powders useful as dielectrics 

 and in rheological studies. Such studies also bear on polymer forms impor- 

 tant in ion exchange resins. 



Several significant factors influencing the preparation of polymer sphe- 

 roids have been established on a semi-quantitative basis: Polyvmyl alcohol 

 proved to be a highly efficient stabilizer for polymer spheroid preparations. 

 Under comparable conditions, (a) high molecular weight grades, (b) par- 

 tially hydrolyzed grades, and (c) high concentrations of stabilizer were 



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

 1 Bell Tel. Labs. 



