ABSTRACTS OF TECHNICAL ARTICLES 743 



one-year outdoor exposure test. Such differences as were found were 

 shown to be due either to deterioration or improvement in the paint 

 film as the result of weathering. 



Characteristics of Modern Microphones for Sound Recording.^ F. L. 

 Hopper. Factors influencing the choice of a microphone for sound 

 recording are considered. The characteristics of a new miniature 

 condenser transmitter and amplifier, as well as a number of other 

 types of microphones now in use, are included. 



Cold-Cathode Gas-Filled Tubes as Circuit Elements.^ S. B. Ingram. 

 The application of electronic devices to the local systems plant is 

 still in its infancy. One of the first of these devices to receive extensive 

 use is the cold-cathode gas-filled tube. As a sensitive relay it is 

 beginning to make its appearance in a number of telephone control 

 and signaling circuits, being best known for its use in the standard 

 four-party subscriber set where its rectifying property enables it to 

 discriminate between positive and negative polarity for selective 

 ringing. Compared with other types of vacuum tubes the cold- 

 cathode tube has the advantages that it operates without cathode 

 heating power, has the ability to start immediately when a signal is 

 applied, and does not deteriorate when not passing current. These 

 advantages make it particularly suitable for use in telephone circuits 

 where intermittent service is common and long life and economical 

 operation are required. 



The paper describes the structure and electrical characteristics of 

 cold-cathode tubes. Their properties as circuit elements are then 

 illustrated in a number of typical basic circuits. 



Indufftive Coordination with Series Sodium Highway Lighting Circuits.^ 

 H. E. Kent and P. W. Blye. This paper describes the wave-shape 

 characteristics of the sodium-vapor lamp and discusses the relative 

 inductive influence of various series circuit arrangements in which 

 such lamps are employed. A method is outlined by means of which 

 the noise to be expected in an exposed telephone line may be estimated. 

 Measures are described which may be applied in the telephone plant or 

 in the lighting circuit to assist in the inductive coordination of the 

 two systems. These measures need be considered only when a con- 

 siderable number of lamps is involved, since noise induction is negligible 



* Jour. S.M.P.E., September 1939. 

 6 Elec. Engg., July 1939. 

 ^ Elec. Engg., ]\x\y 1939. 



