656 BELL SYSTEM TECHNICAL JOURNAL 



horizontal and from vertical antennas. Fading, speech quality and 

 noise are discussed. The results are briefly interpreted in terms of 

 present day short wave theories. 



An Introduction to Ultra-Violet Metallography:- Francis F. Lucas. 

 This paper describes the ultra-violet microscope and the technique 

 of its application to the study of metal surfaces. The ultra-violet 

 microscope can be said to have lived up to expectations. Crisp bril- 

 liant images can be obtained which surpass in quality those obtainable 

 with the apochromatic system. The potential resolving ability of 

 the monochromats can be realized in practice and the practical ap- 

 plication of the ultra-violet microscope should develop much new in- 

 formation. The ultra-violet microscope is the most complicated of 

 any within the realm of technical or scientific microscopy. It re- 

 quires a highly developed technique for its successful manipulation 

 and the specimens must be prepared with great care. The ultra- 

 violet equipment appears to have a potential resolving ability prob- 

 ably greater than twice that of the apochromatic system. 



Portable Receiving Sets for Measuring Field Strengths.^ Axel G. 

 Jensen. Describes a measuring set involving the use of a current- 

 dividing potentiometer accurate for frequencies up to about 1,500 

 kilocycles and having a field-strength range of about 20 to 200,000 

 microvolts per meter. 



Thermionic and Adsorption Characteristics of Caesium on Tungsten 

 and Oxidized Tungsten* Joseph A. Becker. Curves showing the 

 logarithm of the electron current per cm^ from tungsten and oxidized 

 tungsten over a wide range of filament temperatures are given for 

 several vapor pressures of caesium. At high temperatures the tungsten 

 is covered only to a slight extent with adsorbed caesium. As the 

 filament temperature is lowered more caesium is adsorbed. This 

 lowers the electron work function and increases the emission many 

 thousandfold. The process continues until a temperature is reached 

 at which the tungsten is just covered with a monatomic layer when 

 the work function has a minimum value. At still lower temperatures 

 the surface is more than completely covered, the work function 

 increases again, and the emission decreases rapidly. 



2 Presented before the American Institute of Mining and Metallurgical Engineers, 

 New York, N. Y., February, 1926. Published as Pamphlet No. 1576-E, issued with 

 Mining and Metallurgy. 



' Proceedings I. R. E., page :i33, June, 1926. 



•< Physical Review, Vol. 28, pp. 341-361, August, 1926. 



