Abstracts of Technical Articles by Bell System Authors 



Historical Background of Electron Optics} C. J. Calbick. The discov- 

 ery of electron optics resulted from studies of the action, upon electrons or 

 other charged particles, of electric and magnetic fields employed for the 

 purpose of obtaining sharply defined beams. The original Braun tube 

 (1896) employed gas-focusing, as did the low-voltage cathode-ray oscil- 

 loscope developed by Johnson in 1920. It was early discovered that an 

 axial magnetic field could be used to concentrate the electrons into a beam, 

 and this method came into wide use in the field of high-voltage cathode-ray 

 oscillography. In 1927 Busch published a theoretical study of the action 

 of an axially-symmetfic magnetic field upon paraxial electrons, showing 

 that the equation of the trajectories of the electrons was similar to that of 

 the paths of light rays through an axially symmetric optical system. He 

 concluded that such magnetic fields constituted lenses for electrons and pre- 

 sented experimental confirmation. In 1931 Knoll and Ruska presented a 

 large amount of additional experimental material and used the words "elec- 

 tron optics" to describe the analogy. In 1932 Bruche and Johannson pub- 

 lished the first electron micrographs. 



The Davisson and Germer electron diffraction experiments (1927) em- 

 ployed electron beams formed by electron guns consisting of a thermionic 

 cathode emitting electrons which were accelerated by potentials applied to a 

 series of plates containing aligned apertures. The resultant beam was 

 quite divergent. Davisson and Calbick made a theoretical and experimental 

 study of the forms of such beams. They concluded that the distorted elec- 

 tric field in the vicinity of an aperture in a charged plate constituted a lens 

 for charged particles (1931). The optical analogy was either a cylindrical 

 or a spherical lens, according as the aperture was a slit or a circular hole. 

 The theory was confirmed by photographing the forms of electron beams, 

 and by construction of an electrostatic electron microscope whose experi- 

 mental magnification agreed with the theoretical. 



Coaxial Cables and Associated Facilities r J. J. Pilliod. {Summary of 

 Talk before St. Louis Electrical Board of Trade, October 17, 1944.) Coaxial 

 cables provide means of transmitting frequency bands several million cycles 

 in width over a metal tube a little larger than a lead pencil, with a copper 

 wire extending along its axis. Several of these tubes can be placed in a 

 lead sheath. 



The frequency band transmitted over coaxial cables may be split up so as 

 to provide several hundred telephone circuits or, without such division, 



^Jour. Applied Physics, October 1944. 

 '^FM and Television, November 1944. 



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