The Bell System Technical Journal 



January, 1932 



I 



The Cathode Ray Oscillograph* 



By J. B. JOHNSON 



The cathode ray oscillograph, since its invention by Braun, has developed 

 along three lines. The major types of tubes are the high voltage tubes 

 with a fluorescent screen, the high voltage tubes with internal photographic 

 equipment, and the low voltage tubes. This paper follows the structural 

 development of commercial tubes. The operation of the tubes is discussed, 

 from the standpoint of both theory and practice, with particular reference 

 to the low voltage type of tube. Numerous examples are given of the 

 applications of the tubes to problems in science and engineering. 



N our complicated life, we find that we need a great many aids to 



our primary sense organs. The processes of the modern world 

 demand that we make correct estimates of things that are too large or 

 too small, too intense or too feeble, for our poor senses. We have 

 balances to give us the weight of masses too heavy for us to lift or too 

 small to be felt. Telescopes enable us to see far-off objects, micro- 

 scopes very small objects. Our ears are supplemented by telephones 

 that put us within earshot of almost all the civilized world. For elec- 

 tric currents we have ammeters to measure currents so large as to 

 destroy us in a second, and galvanometers that measure currents far 

 too small for us to feel as a shock. Taste and smell have not yet been 

 supplied with artificial aids, but that may come some day. 



For recording long times we have clocks and calendars; for making 

 a record of happenings that take place in a time too short for us to 

 think of, we use oscillographs. 



There are a number of different types of oscillographs in use, all of 

 them electrical in nature. The kind I am going to discuss involves a 

 stream of cathode rays and it is therefore called the cathode ray oscil- 

 lograph. The principle of its operation is quite simple. We have two 

 electrodes in an elongated, evacuated glass tube as in Fig. 1 ; one of 

 them may be a heated filament, the other a plate with a small hole in 

 it. When a potential is applied between the electrodes, making the 

 filament cathode and the plate anode, the electrons emitted by the hot 

 filament are drawn to the anode. Some of them pass through the fine 

 hole in the anode and continue as a thin pencil of electrons, a cathode 



* Presented at Franklin Inst, mtg., Dec. 4, 1930. Jour. Franklin Inst., De- 

 cember, 1931. 



