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BELL SYSTEM TECHNICAL JOURNAL 



greater than that represented by the 10% line, 50 per cent, showed 

 activity greater than the 50% line and 60 per cent, showed activity 

 greater than the £0% line. The three lines illustrating the range of 



-P — - 



A WATTS x 10 



POWER-EMISSION CHART 



Fig. 2 



variation in Fig. 3 do not correspond to these same percentages but 

 have been labeled so as to be readily interpretable. 



The efficiencies in milliamperes of emission current per watt used to 

 heat the filament are shown by the curved lines that cross each chart. 

 Operating temperatures and corresponding filament life are given for 

 certain of the ordinates. The tungsten life data in Fig. 1 are for 

 3-mil wire and a constant heating current. If operating at a con- 



