746 BELL SYSTEM TECHNICAL JOURNAL 



less than those required to form the bridges, field currents exist. 

 These increase rapidly as the field is raised and attain a value around 

 10"^" ampere before the bridges are formed. Calculation of the 

 maximum electrostatic stress on the electrodes at the time of break- 

 down gives a value 0.05 to 0.0005 times the tensile strength of the 

 electrode material at room temperature. The field is locally higher 

 than that calculated because of surface roughness and the tensile 

 strength is probably lowered by the local heating known to accompany 

 field currents. The data therefore indicate that electrostatic force 

 pulls material from the electrodes to bridge the gap. 



Measuring Transmission Speed of the Coaxial Cable}"^ J. F. Wentz. 

 Time of transmission of carrier currents over high speed lines is dis- 

 cussed. A method of measuring this time delay as used on the 

 1000-kc system of the New York-Philadelphia coaxial cable is de- 

 scribed and the results are given for the television band transmitted 

 over it experimentally. 



12 Bell Labs. Record, June 1939. 



