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National Resources Planning Board 



matically the reflecting power or the transmission of a 

 given sample for all wave lengths in the spectrum. 

 Many manufacturers of inks and other materials 

 wherein color must be specified exactly are already 

 using this instrument to make precise colorimetric 

 measurements. 



Electron Microscope 



Much research has been carried out in the last few 

 years on the paths that electrons take when accelerated 

 by grids and rings in tubes. It has been found that 

 certain arrangements of electrodes or coils have exactly 

 the same focusing properties for electron beams as glass 

 lenses have for light beams. Thus it is quite possible 

 to build electron microscopes that are superior to optical 

 microscopes for some purposes. This is particularly 

 true where a heated metal is being observed. Such a 

 metal emits electrons which can be accelerated by ap- 

 plying a small voltage. If these electrons impinge upon 

 a flouorescent screen they produce an optical image 

 that shows variations in the composition or condition 

 of the surface of the metal. Since the lengths of the 

 electron waves can be made as small as desired, there is 



FiGUKE 72. — High-Speed Photographs of Combustion in Gaso- 

 line Engine, General Motors Corporation, Detroit, Michigan 



no limit to the theoretically possible resolution which 

 can be achieved, as there is in an optical microscope. 

 The electron microscope should have many applications 

 in metallurgical and other fields as its properties become 

 better known. 



High-Speed Photography 



For many years high-speed photographs, particularly 

 of sound waves and bullets in motion, have been taken 

 by the light of the electric spark. Until recently this 

 photography has been confined to the laboratory, since 

 it was difficult to obtain sufficient illumination to take 

 ordinary pictures. It has been found, however, that a 

 violent discharge of an electrical condenser through a 

 gas-filled tube provides an intense flash of light of very 

 short duration. With such a flash extraordinary pic- 

 tures of objects in motion can be taken. Striking 

 examples of pictures of a swinging tennis racket, golf 

 club, or other sports equipment have been published 

 in the popular magazines and newspapers. A succession 

 of such pictures show in detail, for instance, how an air 

 bubble is formed by a drop splashing into a liquid 

 surface, or the way in which a golf club is bent in striking 

 a golf ball. Although industrial applications of high- 

 speed photography do not receive the publicity of these 

 other applications, there have been very many useful 

 applications, and there wiU undoubtedly be many more. 

 In the textile industry great difficulty was caused by the 

 snagging of the thread coming off a very high speed 

 spindle. The speed was such that it was impossible to 

 see what made the thread catch. However, a high- 

 speed photograph showed immediately that a loop 

 was being formed as well as how this loop became 

 entangled. In the airplane industry high-speed pho- 

 tography permits the direct measurement of the dis- 

 tortion of a fuU sized airplane propeller. Although the 

 propeller rotates at full speed, it is possible to obtain a 

 precision of 0.02 of an inch in these measurements. 

 The design of silent fan blades was aided by high speed 

 pictures of the formation of vortices using smoke 

 mixed with the air. 



Photoelasticity 



With increased competition in industry, the elimina- 

 tion of excess weight has become a very important 

 factor. To determine the size of any part of an engi- 

 neering structiu-e and exclude unnecessary material one 

 must know how the stresses are distributed. The 

 mathematical calculation of the stress distribution in an 

 irregularly shaped member is often so difficult that only 

 a rough approximation can be made. To obtain more 

 exact analysis of the stress distribution a method has 

 been devised making use of polarized light. This 

 method of analysis has received considerable stimulation 

 in the past few years by the introduction of the material 



