312 BELL SYSTEM TECHNICAL JOURNAL 



It is expected that useful correlation will be found between the nor- 

 mal earth potential effects which occur day after day during undis- 

 turbed periods and the corresponding diurnal and seasonal variation of 

 radio transmission. It seems entirely probable, for instance, that 

 earth potentials are but the terrestrial manifestations of certain changes 

 taking place in the Kennelly-Heaviside layer which may not be found 

 by other methods. 



This paper is intended to serve mainly as a progress report outlining 

 briefly the methods and scope of the work and showing the type of 

 data being obtained. It leaves to a later date most of their correlation 

 and their interpretation. The data here presented are in a conven- 

 tional form used by other investigators for many years. Their value 

 lies mainly in their extent and in the rather wide range of circumstances 

 under which they were obtained. 



Investigation of Rail Impedances.^ Howard M. Trueblood and 

 George Wascheck. Measurements of impedance made on five sizes 

 of rails and on two types of bonds are reported in this paper; the inves- 

 tigation covered a range of current per rail of 20 to 900 amperes, and 

 frequencies of 15 to 60 cycles per second. Results are given in a form 

 convenient for engineering use, and include information for applying 

 corrections for bond impedance and for temperature. 



^ Elec. Engg., December, 1933. 



