ABSTRACTS OF TECHNICAL ARTICLES 121 



third factor and presents theoretical and experimental data showing 

 how this resultant reverberation time may be determined. It is a 

 matter on which little information has been available up to the 

 present time. 



Air- Conditioning System for Low Humidities Required During the 

 Manufacture of Telephone Cables} F. H. Kruger. This paper con- 

 siders the requirements of an air-conditioning system to maintain the 

 necessary humidities and temperatures in the cable storage rooms. 

 The selection, design and performance of a combined refrigeration and 

 moisture adsorption system are described. A two-stage refrigeration 

 system cools and consequently drys the air which is delivered to the 

 adsorption system and to the loop cable storage room for the removal 

 of heat. The adsorption system supplies air of a low moisture content 

 to the toll cable storage room. Air recirculated from the toll room 

 maintains the correct humidities in the loop cable storage room. 

 Silica gel placed in two beds or adsorbers dehydrates the air passing 

 through the adsorption system. An air heater and cooler are suc- 

 cessively used to condition the moistened gel in the adsorbers alter- 

 nately. Finally the distribution of air and the humidity determina- 

 tions in the storage rooms are discussed. 



Photo-conductivity } Foster C. Nix. The influence of light on the 

 flow of current through certain solids had been observed for several 

 decades, but without important results prior to the brilliant work of 

 Gudden, Pohl, and their collaborators. These investigators made the 

 important advance of passing from the study of polycrystalline semi- 

 conductors having comparatively large conductivities, when not 

 illuminated, over to single crystals of insulators. This enabled them 

 to study the conductivity arising when the crystal is irradiated with 

 light of suitable wave-length under simpler and more controllable 

 conditions than had hitherto been obtainable. In many cases they 

 were able, by using feeble light and low voltages, to distinguish 

 between phenomena which they called "primary" or "secondary." 

 The distinction is fundamental and is treated at length in this article. 

 The article begins with an account of the phenomenon designated by 

 Gudden and Pohl as primary and sometimes classified under the name 

 internal photoelectric effect to distinguish it from the so-called external 

 photoelectric effect (i.e., ejection of electrons from substances into 

 surrounding gas or vacuum by incident light). The secondary phe- 

 nomena are then taken up: first in cases where they coexist with 



■I Heating, Piping and Air Conditioning, November, 1932. 

 5 Reviews of Modern Physics, October, 1932. 



