856 BELL SYSTEM TECHNICAL JOURNAL 



measurable current are alterable together by changing the resistance 

 introduced between the grid and filament of the amplifying tube. 

 With tubes of high insulation, the amplification can be made as large 

 as 10''; and the measurable current as low as 10"^'' ampere. Some 

 improvements of the circuit are: (1) the insertion of a resistance in 

 series with the tube in one arm of the bridge to "compensate" for 

 variations in plate and grid battery voltages; (2) the suspension of 

 the tubes to protect them from mechanical vibrations; (3) the use of 

 tubes with pure tungsten filaments to avoid changes in contact 

 potentials, and with plates enclosing the filaments completely to 

 lower the effects of wall charges. In a "null" method of using the 

 circuit the values of the grid resistance and an auxiliary potential 

 introduced in the grid-filament circuit are sufficient to determine the 

 measured current. 



Meeting Long Distance Telephone Problems.'^ H. R. Fritz and 

 H. P. Lawther, Jr. There have been written many papers 

 describing various technical and apparatus developments of value 

 in providing long distance telephone service. Several papers have 

 also appeared covering specific transmission or operating problems, 

 or dealing with the advance planning of the telephone plant. 

 Feeling that it might be of interest, particularly to the young 

 engineering graduates, the writers have prepared this over-all sketch 

 of the general problem of actually providing, year by year, the ex- 

 tensions and additions to a comprehensive network of communication 

 channels necessary to keep pace with a growing public demand for 

 long distance service. Since the writers are most familiar with the 

 area served by the Southwestern Bell Telephone Company, the 

 discussion is restricted to that territory. 



Some Measurements on the Directional Distribution of Static.^ A. E. 

 Harper. The utility of directional data on static is shown, and two 

 types of apparatus devised for such a directional investigation are 

 compared. It is shown that a method which gives the direction of 

 individual crashes is superior to integrating methods. The distribution 

 of thunderstorms over the world is discussed, and comparisons are 

 drawn between this distribution and the observed directional dis- 

 tribution of static. Probable geographical locations are assigned to 

 the sources, based upon thunderstorm data and directional obser- 

 vations. 



M. /. E. E. Journal, July, 1929, pp. 547-550 (abridgment). 



^ Proceedings of the Institute of Radio Engineers, Vol. 17, July, 1929, pp. 1214-1224. 



