ABSTRACTS OF TECHNICAL PAPERS 809 



fresh interest due to the system disclosed by Armstrong * in which 

 high-frequency selectivity and low-frequency balancing are essential 

 features. Armstrong's scheme is treated in more detail in the latter 

 part of this paper. 



The conclusions of this study are entirely negative, that is, no ap- 

 preciable gain is to be expected from balancing arrangements. This 

 is quite in agreement with the conclusion drawn over ten years ago 

 as a result of a rather extended experimental study made in the Bell 

 System. In fact, as more and more schemes are analyzed and tested, 

 and as the essential nature of the problem is more clearly perceived, 

 we are unavoidably forced to the conclusion that static, like the poor, 

 will always be with us. 



Thermostat Design for Frequency Standards.^ W. A. Marrison. 

 A means for maintaining constant temperature is described in which 

 those temperature variations which are essential for operation of the 

 controlling element are prevented from reaching the controlled chamber 

 by a wall of material especially chosen for the purpose. Such a wall 

 1 cm. thick, consisting of alternate thin layers of felt and copper, 

 will reduce temperature variations having a period of one minute or 

 less by a factor of 10,000 to 1. 



Technical Considerations Involved in the Allocation of Short Waves; 

 Frequencies between 1.5 and 30 Megacycles.^ Lloyd Espenschied. 

 This short paper discusses the relation between frequency and distance 

 of transmission for short waves in so far as it affects allocation. A 

 table is given in which the entire short-wave field from 10 to 200 meters 

 is divided into three major bands each containing numerous sub- 

 bands. For each sub-band the number of channels theoretically 

 possible is given and also the number of channels being used at the 

 present time. Factors affecting the separation of channels are also 

 listed. 



Effect of Street Railway Mercury Arc Rectifiers on Communication 

 Circuits.'' Charles J, Daly. This paper describes the effects ex- 

 perienced on the telephone circuits from two mercury arc rectifier 

 substations recently installed in Bridgeport, Conn., and shows in table 

 form the relative magnitude of the interfering effects between rotating 

 equipment and mercury arc rectifiers as a means of energizing the 

 street railway system. The method and the type of apparatus used to 

 reduce the effects experienced from the rectifiers are also described. 



*^ Proceedings of the Institute of Radio Ejigineers, Jan., 1928, Vol. 16, No. 1, p. IS. 



5 Proceedings of the I. R. E., Vol. 16, No. 7, pp. 976-980, July, 1928. 



^Proceedings of the I. R. E., Vol. 16, No. 6, pp. 773-777, June, 1928. 



7 Journai of the A. I. E. E., Vol. XLVII, No. 7, pp. 503-506, July, 1928. 



