688 BELL SYSTEM TECHNICAL JOURNAL 



constant and the field for unit power flow for the gravest mode of hehcal 

 transmission system. 



Traveling-Wave Tubes}'' J. R. Pierce and L. M. Field. Very-broad- 

 band ampUfication can be achieved by use of a traveling-wave type of circuit 

 rather than the resonant circuit commonly employed in amplifiers. An 

 amplifier has been built in which an electron beam traveling with about 1/13 

 the speed of light is shot through a helical transmission Ime with about the 

 same velocity of propagation. Amplification was obtained over a band- 

 width 800 megacycles between 3-decibel points. The gain was 23 decibels 

 at a center-band frequency of 3600 megacycles. 



Attenuation of Forced Drainage Effects on Long Uniform Structures}^ 

 Robert Pope. When forced drainage is applied to an underground metallic 

 structure to provide cathodic protection, the greatest effects on the structure 

 and earth potentials occur in the vicinity of the drainage point and anode. 

 These effects taper off as the distance from the drainage point increases and 

 even in the relatively simple case of a long, uniform structure, the manner in 

 which these effects taper off or attenuate is quite complex. However, by 

 making a few justifiable assumptions, relatively simple equations are devel- 

 oped which provide sufficiently accurate results in most practical cases. 

 Furthermore, the simple equations bring out more clearly the relative im- 

 portance of the various factors involved than do the more rigorous equations. 

 The approximate equations have been used with fair success in predicting 

 the effects of drainage on underground telephone cables in conduit and on 

 buried coated cables. They should apply quite accurately to coated pipes, 

 and there are examples of reasonably good application on some bare pipes. 



The soil and structure characteristics which enter into the equations are 

 discussed, and the units used established. 



Alkaline Earth Porcelains Possessing Low Dielectric Loss}^ M. D. Rig- 

 TERINK and R. O. Grisdale. Alkaline earth porcelains have been prepared 

 from mixtures of clay, flint, and synthetic fluxes consisting of clay calcined 

 with at least three alkaline earth oxides. These porcelains possess excellent 

 dielectric properties, have low coefficients of thermal expansion, are white, 

 and are especially valuable as bases for deposited carbon resistors for which 

 they were developed. Their characteristics make it probable that other uses 

 will be found for materials of this type. 



An illustrative composition is 50.0% Florida kaolin, 15.0% flint {?>15 



'Tr0C. LR.E., February 1947. 



" Corrosion, December 1946. 



" Jour. Amer. Ceramic Soc, March 1, 1947. 



