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graph and radiograph, Fig. 7. In these gaps the sparking area of the 

 cathode was hemispherical in shape, partly surrounding a spherical anode. 

 These gaps were operating successfully at the end of 1000 hours. The 

 scattered material was deposited on only a portion of the glass envelope of 



Fig. 7— Photograph and radiograph — actual size — of the first unit type gap having a 

 re-entrant aluminum cathode, a spherical aluminum anode and a hydrogen-argon gas 

 atmosphere, after operating 1000 hours with a 40 ampere pulse of one microsecond dura- 

 tion relocated 1660 times a second. 



each gap, as shown in the photograph. The extent of the material removed 

 from the cathode and deposited on the anode, as shown in the radiograph, 

 was such as to cause no marked change in gap spacing. Furthermore, the 

 operating range remained substantially constant throughout the 1000 hours 

 of operation as shown in Fig. 8. This was an important observation since it 



