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National Resources Planning Board 



cause of this uncertainty made it possible to develop a 

 cure. By means of a rigid guide above the drill bit and 

 by the accurate control of the pressure on the drill, 

 holes can now be sunk to any required depth without 

 significant change in direction. 



Another very important and profitable study that 

 has been made by physicists is concerned with the flow of 

 oil in rocks. Oil is usually found in a variety of 

 porous rocks such as sandstones or limestones. The 

 rate at which it can flow through a porous rock was 

 determined in the laboratory. From these studies the 

 rate at which oil can be removed from deposits of limited 

 area without restricting the total output is now under- 

 stood and may have considerable economic importance. 



It is perhaps worth emphasizing again that what 

 physics has done in the oil industry is to teach the 

 principles that are applicable, to develop instruments 

 that are sufficiently sensitive and rugged to make meas- 

 urements in the field, and to interpret the measurements 

 in terms of subterranean structure. It has changed 

 oil prospecting from a matter of chance to an exact 

 scientific procedm-e which has enormously increased the 

 availability of sources of oil. 



The Lamp Industry 



The application of physics in the development of 

 the various types of illumination in the last 30 or 40 

 years provides another example of its use in industry. 

 It was early realized that electrical energy may be used 

 to produce light. The simplest and the most direct way 

 to accomplish this is to allow the electrical energy to 

 heat a solid to incandescence. The most convenient 

 form that such a solid could take for tliis purpose is a 

 long, high-resistance filament, and the earliest practicable 

 filament was the carbon filament originally developed 

 by Edison. It had its imperfections in that the tem- 

 perature at which it could be operated was low, its life 

 was short, and the color of the light produced was red- 

 dish. The ambition to produce a more efficient 

 filament from these standpoints stimulated the work on 

 tungsten and other materials. Much of this work is of a 

 physical nature and was carried out in physics labora- 

 tories. Many things had to be studied. Fu'st of all, 

 it was found impossible to draw timgsten into a fine 

 filament. Cooperation between physicists and metal- 

 lurgists finally resulted in the production of ductile 

 tungsten. 



Then began the most interesting part of the develop- 

 ment. A careful study of the radiation, the effect of the 

 temperature of the filament on the nature of the light 

 emitted and on the life of the filament, gradually pro- 

 vided information that became useful. Originally the 

 filaments were operated in a vacuum. A study of the 

 effect of the presence of inert gases on the evaporation 

 and the deterioration of the filament showed that it was 



advantageous to surround the filament with such a gas 

 at appreciable pressures. The presence of the gas re- 

 tarded evaporation and permitted the operation of the 

 filament at a very much higher temperature. The 

 higher temperature produced whiter light, and also re- 

 sulted in the emission of a greater portion of the energy 

 in the visible part of the spectrum, giving a higher 

 efficiency. In the construction of these lamps it was 

 necessary to apply physical apparatus and measm-ing 

 instruments in many ways. It was necessary, for in- 

 stance, to study metal-to-glass seals so as to produce 

 a perfectly airtight bulb in which the filament could be 

 housed. This necessitated the comparison of coeffi- 

 cients of expansion of various kinds of glass and metal 

 and the development of combinations of glasses and 

 metals to make seals that were absolutely tight at ordi- 

 nary temperatures and that remained so during the 

 heating and cooling which the lamp experiences in use. 



The study of the radiation from the filament itself 

 required the use of optical pyrometers, with which it 

 was possible to determine the exact temperatures of the 

 filament at any one spot. To avoid false readings from 

 the surface, the filaments were made tubular and the 

 temperature of the interior was read tlu-ough very 

 minute holes through the side of the tube. 



Photometric measurements were necessary to deter- 

 mine the light intensity of the source. To obtaLa use- 

 ful information these measiu-ements had to be made in 

 all directions from the lamp, thus enabling one to inte- 

 grate the total radiation either mathematically or by 

 means of integrating photometers. A spherical photo- 

 meter, with which the total amount of light in all di- 

 rections could be determined by a single reading, was 

 one of the physical developments that resulted. It was 

 desirable also to determine the distribution of light 

 throughout the spectrum. This feat was accomplished 

 by applying the photometer to individual portions of 

 the spectrum in an apparatus known as a spectrophoto- 

 meter. 



In the early stages of the development of the modern 

 lamp, the research laboratory assigned itself the job 

 of finding out everytliing it possibly could about heated 

 filaments. One of the discoveries was that the inert 

 gas used in the lamp formed a sheath around the fila- 

 ment and thus decreased the rate of evaporation. By 

 coiling the filament springwise this protective sheath 

 became more effective, and the efficiency was increased. 

 The rather novel suggestion was then made to coil the 

 coil into sort of a superspring. On trial, it was found 

 that this procedure increased the efficiency still further, 

 and it is done in making most of our lamps of today. 



This brief history of the research on the incandescent 

 lamp illustrates well how the physicist works. Ordi- 

 narily he is not trying to make minor improvements in 

 design. Instead he studies the fundamental process 



