6 BELL SYSTEM TECHNICAL JOURNAL 



Having now described in an elementary way how the cathode ray 

 oscillograph works, let me turn to the story of the development of the 

 tube.i The first reference I have seen to the idea that a cathode ray 

 might be used to indicate magnetic field dates to 1894, when Hess,^ in 

 France, suggested the use of such a tube as a curve tracer. The first 

 application of the idea, however, was made by Ferdinand Braun » in 

 1897, and after him the instruments have been called Braun tubes. 



Fig. 6 — The first cathode ray oscillograph, F. Braun, 1897. 



The tube of Braun was quite simple (Fig. 6). It had a flat disc 

 cathode, a wire in a side tube as anode, a pierced diaphragm to limit 

 the beam and a fluorescent screen of zinc sulphide. It contained air 

 at low pressure. Current from an electrostatic machine produced a 

 discharge in the residual gas in the tube, from which emanated the 

 cathode rays through the aperture in the diaphragm. 



Fig. 7 — Tube for measuring e/m, J. J. Thomson, 1897. 



It is of interest that the invention of the tube took place before the 

 nature of cathode rays was understood. It was in the same year that 

 J. J. Thomson in England and W. Kauffmann in Germany, each 

 using a tube that was almost identical with the Braun tube, deter- 



1 More detailed chronicles of the development of the tube have been made by H. 

 Ilausrath, "Apparatus and Technique for Producing and Recording Curves of Alter- 

 nating Currents and Electrical Oscillations," //e//o5, 1912; and by MacGregor-Morris 

 and Mines, "Measurements in Electrical Engineering by Means of Cathode Rays," 

 JL Inst. El. Eng., 63, p. 1056, 1925. 



2 Hess, A., Compt. Rend., 119, p. 57, 1894. 

 •Braun, Ferdinand, ]]'icd. Ann., 60, p. 552, 1897. 



