478 BI'-LL SYSTEM TECHNICAL JOURNAL 



stations are nonisochronous and transmit different programs. A 

 discussion of the characteristics of shared channel interference is given, 

 and it is shown that there are only two important components of this 

 interference, one being the carrier beat note and the other being what 

 has been designated as side band noise. This latter consists of two 

 frequency spectra, one of which is similar to the spectrum of the mod- 

 ulating frequencies of the undesired station but is shifted upward by a 

 constant amount equal to the difference between the carrier fre- 

 quencies. The other spectrum is of a similar type but is shifted down- 

 w^ard in frequency by the same amount. 



The Use of Thermionics in the Study of Adsorption of Vapours and 

 Gases.^ Joseph A. Becker Thermionic emission can be very useful 

 in the study of adsorption phenomena. The primary reason is that 

 very minute amounts of electropositive elements, such as caesium, 

 barium, or thorium, or electronegative gases, such as oxygen, change 

 the thermionic emission from surfaces of tungsten, platinum, molyb- 

 denum, etc., by very large factors and in a characteristic manner. 

 They do this by changing the work function of the surface. This 

 effect, as well as other surface effects, can be best explained by the 

 adion grid theory: The adsorbed particles can exist on the surface 

 either as adions (adsorbed ions) or as adatoms; the adions act like a 

 positively charged, open meshed grid placed very close to the surface. 

 From this theory and the experimental facts it follows: (1) That the 

 ratio of adions to adatoms decreases as the surface concentration in- 

 creases (Table I) ; (2) that the work required to remove an adion from 

 the surface increases while the work to remove an adatom decreases 

 as the surface concentration increases; (3) the mean life of an adsorbed 

 particle depends on the surface concentration as well as on the tem- 

 perature (Table II); (4) the rate of diffusion from the surface into the 

 interior depends upon the temperature and on the amount by which 

 the surface concentration exceeds its equilibrium value. Thermi- 

 onic experiments show the existence of surface migration and can be 

 used to make a quantitative study of this phenomenon. The tech- 

 niques involved in these various experiments are described and refer- 

 ences given to previous publications. 



Electrical Phenomena in Gases.^ Karl K. Darrow. This treatise 

 of 500 pages is concerned with one of the most important, instructive, 

 and intensively studied fields of modern physics. Its scope embraces, 

 first of all, the elementary processes through the action of which a gas 



^Transactions of the Faraday Society, March, 1932. , ,r,.^ 



'Published by Williams and Wilkins Company, Baltimore, Maryland, 1961. 



I 



