12 



BELL SYSTEM TECHNICAL JOURNAL 



In the last couple of years a further step has been made by Max 

 Knoll. ^^ He seems to have simplified the operation of the tube con- 

 siderably by attaching on the end of his tube a thin window in the 

 manner of Dr. Coolidge's cathode ray tube. In this way the photo- 

 graphic plate on the outside of the tube is exposed to the pencil of 



Fig. 17 — VVestinghouse-Norinder, 1928.^' 



cathode rays that has come through the thin window of metal or of 

 cellophane. 



We have, then, three general classes of cathode ray oscillographs: 

 First those that resemble the original Braun tube, still in limited use, 

 comprising a glass tube with a fluorescent screen, and a relatively high 

 operating voltage; second the tubes of the Dufour type that I have 

 just described, with direct recording on the photographic plate or 



16 Knoll, Max, Zeits. f. tech. Phys., 10, p. 28, 1929. 

 " Norinder, H., A. L E. E. Trans., 47, p. 446, 1928. 



