Industrial Research 



245 



known as "polaroid," which enabU>s lart;c beams of 

 polarized light to bo formed at low expense. If one 

 uses two sheets of polaroid with their axes at right angles 

 to one another, no light will penetrate; however, if a 

 celluloid model of a particular engineering structure is 

 placed between those two sheets of polaroid and a load is 

 added, the points of maximum stress become bright 

 with closely spaced bands of color. It has been possible, 

 for instance, to reduce greatly the weight of an eyebolt 

 by cutting away those parts shown under polarized 

 light to be of little use for carrying the stress. By 

 careful measurements with polarized light combined 

 with accurate measurements of the change in thickness, 

 it is possible to make a complete analysis of the dis- 

 tribution and magnitude of all of the stresses. This is 

 particularly easy to do in thin and plane objects, but 



by recent methods can also be done for objects of 

 irregular dimensions. 



Electron Diffraction 



A remarkable discovery was made in an industrial 

 research laboratory a few years ago. This discovery 

 was that an electron behaves as though it has associated 

 with it a wave length in the same sense that light waves 

 and X-rays have wave lengths. When electrons pass 

 through a thin layer of any material or are reflected 

 from its surface and allowed to impinge on a photo- 

 graphic plate, they make a permanent record of a 

 diffraction pattern similar to what one sees when looking 

 at a distant light through an umbrella. The pattern is 

 characteristic of the material placed in the path of the 

 electrons. An electron diffraction camera is a relatively 



FiouKJi 73. — Photoelastic Pattern of Roller Bearing Stresses Points of Maximum Stress Occur Where the Lines are Spaced tlu' 



Closest, Timken Roller Bearing Company, Canton, Ohio 



