238 



National Resources Planning Board 



carbon dioxide, or of any one of a great number of 

 other individual gases entirely independently of the 

 presence of other impurities. In this method also the 

 selective absorption of light by difFcrcnt materials is 

 basic. 



Communication 



Other illustrations of the way in which physics has 

 contributed to our everyday life may be taken from the 

 field of communication. In the physics laboratories of 

 35 or 40 years ago a great deal of work was done on the 

 discharge of electricity through gases at low pressures. 

 From these experiments, physicists learned of the 

 existence of electrons and of their behavior under 

 various conditions. They learned that an incandescent 

 filament is a copious source of electrons and how to 

 control these electrons. These studies led to the devel- 

 opment of vacuum-tube amplifiers, without which our 

 modern communication systems would be unpossible. 

 These vacuum-tube amplifiers form the basis of the 

 communication equipment used in radio, in carrier- 

 current telephony and telegraphy, and in any apparatus 

 in which the current is too weak to operate instruments 

 or apparatus directly. Thus there has been made 

 possible not only longer overland communication but 

 overland and transoceanic communication without 

 wires or cables, the communication from ship to shore 

 and vice versa, communication between trains and 

 stations, between airplanes, between airplanes and 

 their landing fields, and between police offices and 

 police cars. These are all two-way communications. 

 The currents set up in the receiving apparatus in each 

 case are so feeble that their usefulness would be prac- 

 tically negligible without help from vacuum-tubes. It 

 can be truly said that the whole art of electrical com- 

 munication is a product of physics, and physicists have 

 led in its technical advance. 



The Nature of Physics 



From the illustrations given above it is possible to 

 develop a definition of physics and to give a fairly clear 

 idea of what a physicist is and docs. In its broadest 

 sense physics includes in its scope the study of all the 



Figure 71. — Vacuum Tubes for the Production of Ultrashort 

 Electromagnetic Waves, Bell Telephone Laboratories, New- 

 York, Xew York 



materials and forces of nature. It will have been 

 noted that physics furnished the fundamental principles 

 of the developments which have been described. The 

 physicist also developed apparatus in which these 

 fundamental principles were applied. The investi- 

 gations in physics laboratories proceed from the dis- 

 covery of a new principle and the study of its various 

 applications to the determination of its place in the 

 larger scheme. 



When this work is successful it gives complete 

 quantitative relations and enables one to predict what 

 will happen under given circumstances and to set up 

 the apparatus to produce desired results. If the phe- 

 nomenon is a new one of wide application, such as the 

 electromagnetic relations that form the basis of the 

 development of dynamo-electric machinery, or such as 

 the physical characteristics of metallic filaments that 

 could be used in incandescent lamps or electronic tubes, 

 the result is the creation of a completely new industry 

 or even of many industries. 



Physics has been described as the science of energy 

 transfonnations, and if one studies the fields mentioned 

 above it is seen that this definition applies very gener- 

 ally. Dynamo-electric machines, for instance, transform 

 the energy of heat in the steam engine to electrical 

 energy in the dynamo. In the motor, electrical energy 

 is transformed into mechanical energy to be used in the 

 apparatus being driven. In telephony the transforma- 

 tion is from sound energy to electrical energy, and back 

 again to mechanical energy and soimd. In instruments 

 also it can be shown that Ln nearly all cases the action 

 depends upon a transformation of energy from one form 

 to another. In a clock the transformation is from the 

 potential energy of a coiled spring or of raised weights 

 to the kinetic energy of the pendulum and the moving 

 wheels, and finally part of the energy is dissipated as 

 heat through the friction of the moving parts. In all 

 cases energy is transferred from one part of the apparatus 

 to another, and in the transfer it is also frequently 

 changed from one form to another. All such apparatus 

 and instruments are products of physics. 



Physics Specializes Effectively in 



the Problems of Individual Industries 



The Oil Industry 



In the oil industry one of the problems that has been 

 attacked by physicists is the exploration for new oil 

 deposits. The problem is to find rock structures that 

 are typical of locations where oil is to be foimd. One 

 approach to this problem is based on the fact that 

 different layers of rock have different densities, and any 

 initial deformation in a stratum relative to the other 

 strata in the district will produce a change in the gravi- 

 tational attraction for bodies on the surface of the earth. 



