Abstracts of Technical Articles by Bell System Authors 



Thermionic Emission, Migration, and Evaporation of Barium on 

 Tungsten.^ J. A. Becker and G. E. Moore. When barium is de- 

 posited on tungsten, the thermionic activity of the tungsten increases, 

 comes to a maximum, and then decreases. It has frequently been 

 found by emission measurements that this optimum corresponds to 

 about a monomolecular layer. However, data obtained in this work 

 show that some regions of the filament require more than five times as 

 much barium as others for optimum emission. 



Photographs are presented which show that the rates of both migra- 

 tion and evaporation depend on the crystal surface, the temperature, 

 and amount of barium on the surface. Barium migration on tungsten 

 can be observed at temperatures as low as 970° K., is readily observed 

 at 1025° K., and is rapid at 1070° K. Evaporation is observed on some 

 crystals at temperatures as low as 1025° K., while on others it is slow 

 even at 1260° K. At 1300° K. it is rapid for all crystals. These tem- 

 peratures probably vary with the oxygen contamination which comes 

 over to the filament with the barium. For barium concentrations near 

 the optimum there exists a range of temperature over which migration 

 is readily observed, but where evaporation is not noticeable. 



Measurements of electron emission after all the barium is evaporated 

 show that the filament was contaminated by an electronegative ma- 

 terial, probably oxygen. 



Barium tends to migrate toward the negative end of the filament, 

 thus indicating ionization of adatoms. 



A mechanism for migration is suggested. 



The Vocoder — Electrical Re-creation of Speech.^ Homer Dudley. 

 In the Bell Telephone Laboratories have been developed electrical 

 circuits for the artificial production of speech. One form of the device 

 is itself voice-controlled, thus differing fundamentally from the Voder 

 of the World's Fair which is controlled by keys and pedals. It has 

 been christened the "Vocoder" or "voice coder." 



Many startling effects are possible when the code is varied, for the 

 Vocoder then re-creates sounds quite different from those used by the 

 person speaking. Cadences may become monotones, rising inflections 

 may be turned to falling inflections, a vigorous voice may become a 



1 Philosophical Magazine, February 1940. 



2 Jour. S. M. P. E., March 1940. 



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