ABSTRACTS OF TECHNICAL ARTICLES 839 



mann formula when the value of n is chosen to agree with the valence 

 of the metal. Data are presented showing this condition to be general 

 for the alkali metals, a maximum response to red or infrared light 

 being dependent upon the formation of a subvalent compound, as a 

 suboxide. 



Attention is called to seemingly analogous phenomena in the fields 

 of photoelectricity, photography, fluorescence and absorption. 



Some Problems in Short-Wave Telephone Transmission.^ J. C. 

 ScHELLENG. In this paper are discussed certain phases of short-wave 

 telephony, primarily, though not entirely, from the point of view of the 

 transmitter. The field strengths which the transmitting station must 

 provide at the receiver are considered. Typical data are given showing 

 results obtained in transmission from Deal, New Jersey, to England. 

 This is followed by a discussion of requirements and limitations of the 

 transmitting antenna. The gains which arrays may reasonably be 

 expected to provide are considered. The phenomenon of non-syn- 

 chronous fading at nearby points is examined as to its bearing on the 

 dimensions and performance of directive arrays. Other directional 

 properties of the transmitting medium are also considered. Attention 

 is then directed to the transmitting equipment, particular attention 

 being given to the high-power part of it. Requirements, rather than 

 circuit details, are emphasized. These include stability of operation, 

 flexibility, and freedom from amplitude distortion, and phase and fre- 

 quency modulation. The results of tests in which some of these 

 matters were considered quantitatively are given. 



A Chronographic Method of Measuring Reverberation Time.'' E. C. 

 Wente and E. H. Bedell. Reverberation time measurements are 

 generally made with the ear and a stop watch in the manner devised 

 by Prof. Wallace Sabine. Surprisingly consistent results can be ob- 

 tained by this method in a reverberation chamber, where the rate of 

 decay of sound is slow and where disturbing sounds are absent. But 

 such measurements present difficulties if the room is noisy or if the 

 reverberation time is short. Also it is recognized that uncertainties 

 may be introduced because of the fact that the threshold of hearing 

 varies between individuals and with time in the same person. It was 

 with the object of overcoming these difficulties that the electrical 

 method described in this paper was devised. This method does not 

 differ essentially from that of Sabine except that an electro-acoustical 

 ear of controllable threshold sensibility is substituted for the human ear. 



*Proc. 7.i?.£., June, 1930. 



^Jour. Acous. Soc. Amer., April, 1930, 



