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Natioiml Resources Planning Board 



already been mentioned. As a result of the study of 

 the behavior of hot filaments, the discovery has been 

 made that electrons are given out by incandescent solids, 

 that these electrons will carry currents, that the number 

 emitted depends upon the nature of the hot surface, 

 and that they can be controlled by a very small amount 

 of energy applied to an adjacent electrode. These 

 discoveries resulted in the development of the vacuum- 

 tube amplifier, without which modern loud distance 

 communication would be impossible. Likewise elec- 

 tromagnetic and crystal filters were developed, which 

 enabled the communications engineer to select from the 

 complete range any band of frequencies that he wished. 

 A very important scries of investigations concerned 

 magnetic characteristics of materials that could be used 

 as cores for transformers and for loudspeakers, or ear- 

 phones, and of the permanent magnetic materials that 

 were used in combination in some of the later types of 

 apparatus. 



These studies of fundamental principles and the devel- 

 opment of materials and apparatus to provide efficient 

 means for the necessary energy transformations are in 

 the field of physics. Thus we have an example in which 

 many different branches of physics have converged to 

 produce one practical accomplishment of immeasur- 

 able value to society. On the other hand, in many 

 cases a single development in physics, the vacuum tube 

 for instance, has produced entire new industries and 

 has found practical applications in almost every 

 industry. 



Physics Supplies the Instruments 

 for Measurements in Industry 



One of the many accompHshments of physics has 

 been the development of instruments. For instance, 

 in aviation we have measuring instruments for deter- 

 mining the direction of flying, the orientation of a plane, 

 the location of a landing field when "flying blind," the 

 speed of the plane, the drift of the plane, the distance 

 from the ground, etc. Many different devices have 

 been developed for each one of these purposes, and all 

 are based on a direct application of physical principles. 

 That the instrumentation has already reached a high 

 state of development is evidenced by the remarkable 

 safety records of our commercial air lines. 



Such applications of instruments and measuring 

 devices in any particular field could be multiplied prac- 

 tically ad libitum. We shall, however, content our- 

 selves with mentioning a few specific instruments which 

 are in regular use at the present time. 



Noise meters, a development which has been con- 

 tributed to largely by the telephone development 

 described above, enable anyone to determine the level 

 of disturbing noises in an industrial plant or on a street, 

 to determine the origin of the noises and in that way to 



supply the first essential knowledge toward their 

 elimination. 



Another interesting instrument that has come into 

 use in the last few years is a vibration meter, which can 

 be applied to any piece of machinery to determine the 

 magnitude, direction, and exact nature of its vibrations 

 and to lay the foundation for the elimination of the 

 undesirable vibrations. 



X-rays serve many purposes, such as finding blow- 

 holes in castings, faults in rolled steel, or faults in welds. 

 They can be used also for analyzing crystals or deter- 

 mining the exact crystal structure of a material, and 

 even the distances between the atoms in the different 

 layers of the crystal. X-rays are of great importance 

 in metallurgy and in the physical study of structural 

 materials. 



The cathode-ray oscillograph is a recent addition to 

 instruments that are useful for studying electric circuits. 

 It depends on the action of an electric or a magnetic 

 field on a beam of electrons and makes it possible to 

 observe at a glance the wave form or the nature of the 

 distortion in an electric current produced by any piece 

 of apparatus that is subjected to study. The cathode- 

 ray tube is used in television, position indicators in 

 flj^ing, and in many other applications. 



The sterilizing effect of ultraviolet radiations of 

 certain frequencies has been investigated by physicists 

 in cooperation with biologists and others and has 

 resulted in the development of a lamp which produces 

 radiations of a frequency peculiarly adapted to destroy- 

 ing infection or undesirable germ life of any kind. It is 

 applicable in medicine, in the food industry, in the 

 purification of water, and in the sterilizing of eating 

 utensils. 



Physics Prepares Apparatus for 

 Later Applications in Industry 



Instruments of great value to industry are often born 

 in the laboratory of the pure scientist. In an effort 

 to extend the frontiers of knowledge new instruments or 

 new methods of developing extreme pressures, high 

 speeds, high or low temperatures, etc., are discovered 

 which go far beyond what are considered present needs 

 of industry. It seems profitable to review some of the 

 present procedm-es of the laboratory to find those most 

 likely to be used more extensively in the future in 

 industry. 



High-Speed Centrifuge 



High rotational speeds have long held the interest of 

 physicists. Recently, new advances in experimental 

 technique have allowed rotational speeds as high as 

 20,000 revolutions per second to be obtained. The 

 only reason for this limit is that the rotator flies apart 

 at appreciably higher rotational speeds. The centrifu- 



