Industrial Research 



241 



of converting heat energy into lifi;lil. As a result his 

 progress seems slow. He is not able lo predict before- 

 hand just what he will find or what changes he will 

 make. Yet he can always be sure that the more he 

 knows about these fundamental processes the greater is 

 his chance of producing a major improvement. In the 

 lamp industry each improvement took from 5 to 10 

 years of research, yet each repaid the company many 

 times over for its investment. Since the time of Edison 

 the efficiency of the lamp has been improved almost a 

 thousand percent. It has been calculated that if 

 Edison's lamps were used to produce our present il- 

 lumination our annual light bill would be $3,500,000,000 

 greater than it is at present. 



A more recent development in light sources goes back 

 to another branch of physics; namely, to the electric 

 discharges in gases at low pressures. In the nineties 

 of the last century, experiments with such tubes were 

 very popular in physics laboratories. Although these 

 experiments were performed without immediate prac- 

 tical purposes in mind, it has been found in the last few 

 years that the light so produced may be used as a source 

 of very practical illumination. The color produced by 

 the passage of electricity through a gas depends upon 

 the nature of the gas, and different gaseous combinations 

 give varied light effects. The striking colors produced 

 are used extensively today in advertising. High- 

 intensity mercmy and sodium vapor lamps are used 

 for airport and highway lighting, searchlights, and other 

 purposes. By introducing fluorescent materials into 

 the glass tube in which the discharge is taking place it 

 is possible to produce colored and also nearly white light 

 with extremely high efficiency. The various stages of 

 development from the discharge tube to a practical 

 source of light with an efficiency considerably gi'eater 

 than that of the incandescent filament is a long and 

 interesting story, but in its essentials it is similar to that 

 of the incandescent filament lamp. 



The Communications Industry 



The field of commmiication has already been men- 

 tioned as one in which the application of physics has 

 been important. In a wire as in a radio telephone the 

 sequence of operations calls into play an unusual num- 

 ber of physical principles and also a vast number of 

 different types of apparatus used to transform physical 

 energy. The sequence is about as follows: The voice 

 produces disturbances in the air which move the dia- 

 phi'agm of a microphone. The diapliragm produces a 

 change in pressure on the carbon granules assembled 

 in a capsule, and thereby produces modulations of the 

 current through the carbon granules. This current is 

 sent out on the line either directly or else amplified 

 through vacuum tube amplifiers to increase its power. 

 If it is desired to transmit several messages over a pair 



of wires at the same time, so-called carrier telephony is 

 used, in which the voice current changes or modulates 

 a carrier current of a higher frecjuency. After the 

 modulation it may again be amplified and passed to a 

 teleplione line or cable, or in the radio telephone, to a 

 radiating antenna. If the receiving station is far away 

 there may be vacuum-tube repeaters to pick up the 

 message and transmit it at a higher power level. At the 

 receiving end another filter ])icks one message out of a 

 great number, an amplifier increases its power, a de- 

 modulator separates the voice frequencies from the 

 carrier frequency, and finally an earphone or the 

 loudspeaker directly transmits the sound to listeners. 

 Thus, the telephone is a peculiarly good example of 

 the fact that physics is the science of energy transfor- 

 mations. The following sequence of energy transfor- 

 mations are represented: Mechanical energy of the 

 vocal cords is changed into mechanical energy in the 

 form of compressions and rarefactions in the air, which 

 is then used to energize the diaphragm of the micro- 

 phone. This energy is transformed into electrical 

 energy of the same frequency by the action of the 

 diaphragm on the carbon granules. The electrical 

 energy is amplified, modified, and transmitted over the 

 line or tlu'ough space. During these steps the electrical 

 energy is progressively changed, but it remains electrical 

 or magnetic until it reaches the diaphi-agm of the ear- 

 phone or the loudspeaker. Here it is transformed into 

 mechanical energy again. The diaphram of the loud- 

 speaker agitates the atmosphere and the listener receives 

 the mechanical rarefactions and condensations in the 

 air on his eardrum. 



The remarkable developments in telephone communi- 

 cation have resulted from the convergence of physical 

 investigations in many different fields. First of all 

 there have been the investigations of sound production 

 by the vocal cords and of the modification of that sound 

 by the shape of the mouth and related cavities. Meth- 

 ods of analysis of sounds, both vocal and instrumental, 

 have been developed to determine their component 

 frequencies, the relative energies in these frequencies, 

 and the ways in which they combine and can be repro- 

 duced and separated out again as a result of the com- 

 pound vibrations or responses of electrical, magnetic, 

 electronic, and mechanical devices. 



Other investigations that have converged on the 

 effective transmission of sound have been the study of 

 responses of diapliragms and of their construction so as 

 to make the responses as nearly uniform as possible over 

 the audible range, and the study of the behavior of 

 masses of carbon granules, both as regards the resistance 

 of the mass and the variations of these resistances with 

 pressure, and the reproducibility and permanence of 

 such resistance changes. The contributions of the early 

 experiments on electrical discharges in gases have 



