﻿820 



Mr. K. K. Smith on Negative 



smaller for this lamp than for the other sealed lamps. The 

 only known difference in treatment to which this can be 

 ascribed is that this filament was never heated to a tempera- 

 ture so high as 2700° K., and to avoid the risk of burning 

 out the filament, the temperature was seldom raised above 

 2500° K., except for short periods while observations were 

 being taken. The close agreement indicated in Table III. 



Table III. 



Lamp 7. 



T. 



Current in microamperes per sq. cm. 



1760°K 



Observed. 



37-5 



75-0 



150- 



300- 



600- 



1200- 



2400- 



4800- 



9600- 



19200- 



38400- 



76800- 



154000- 



308000- 



616000- 



1230000- 



Calculated. 



33-8 



78-0 



157- 



295- 



607* 



1260- 



2460- 



4730- 



9680- 



19300- 



37800- 



76700- 



157000- 



311000- 



597000- 



1190000- 



1800 



1840 



1875 



1920 



1965 



2010 



2050 



2105 



2155 



2205 



2265 



2330 



2390 



2455 



2520 





a = 4*4 X 10 s amperes per sq. cm. 

 b = 59700. 



does not, of course, prove that the emission was characteristic 

 of the pnre metal alone. An oxide, for example, could 

 remain upon the wire indefinitely if the temperature were 

 not raised too high. Four months after the lamp was 

 sealed, experiments showed that the emission was unchanged. 

 The filament was then heated to 2900° K. for three minutes, 

 with a potential difference applied to prevent the thermionic 

 current from flowing, but this produced little, if any, change 

 in the emission at 1800° K. The temperature was then 

 raised with the thermionic current flowing, but unfortu- 

 nately the filament was burnt out near one end before any 

 observations could be taken. 



