606 BELL SYSTEM TECHNICAL JOURNAL 



Motion Pictures in Relief.^ Herbert E. Ives. In this article Dr. 

 Ives describes the method by which stereoscopic motion picture 

 projection can, theoretically at least, be attained. The method is 

 relatively complicated and has severe practical limitations. It appears 

 to be theoretically sound and capable of realization, at least on an 

 experimental scale. 



The Absorption of Oxygen by Rubber} G. T. Kohman. The work 

 reported in this paper was planned for the purpose of determining the 

 part played by oxygen absorption in the natural aging of rubber. 

 To do this, the effects of a number of factors known to influence natural 

 aging on rates of oxygen absorption were studied. A piece of appa- 

 ratus, developed for determining these rates, which involves special 

 means for keeping the oxygen pressure surrounding the sample constant 

 is described. The results obtained lead to the conclusion that oxygen 

 absorption is the predominating factor in the natural aging of rubber 

 and that rates of oxygen absorption are of value in predicting the 

 natural life of rubber. 



An Electrical Test for Tin Coating on Copper Wire.'' H. M. Larsen 

 and C. M. Underwood. The method described is essentially a 

 deplating process. The wire samples are placed in an acid solution 

 and a current of suitable value applied to effect the deplating. The 

 weight of tin on the wire surface and that alloyed with the copper are 

 determined separately, the measuring means being two graduated 

 tubes containing electrodes (sometimes called voltameters). The gas 

 evolved in these voltameters is proportional to the current and hence 

 to the tin being removed. As soon as the copper surface is exposed, 

 an auxiliary electrode in the deplating bath actuates a relay which 

 brings into operation the second voltameter, permitting determination 

 of the tin alloyed with the copper. 



Very simple formulae permit determining the amount of tin from the 

 volume of gas accumulated in the two voltameters. The method is 

 said to save time and permit the use of relatively unskilled operators as 

 compared with the usual chemical tests applied to tin coatings. 



Further Observations on the Microstructure of MartensiteJ Francis 

 F. Lucas. This paper is a further contribution by Dr. Lucas on the 

 microstructure of martensite. It describes a number of quenching and 



* Journal of the Optical Society of America and Review of Scientific Instruments, 

 Vol. 18, February, 1929, pp. 118-122. 



* Journal of Physical Chemistry, Vol. ii, February, 1929, pp. 226-243. 

 « Wire &■ Wire Products, Vol. 4, April, 1929, pp. 118-119, 140. 



' Transactions of the American Society for Steel Treating, Vol. 15, February, 1929, 

 pp. 339-364. 



