﻿Thermionic Currents from Tungsten. 811 



Table I. shows the values o£ the currents which best re- 

 present the emission observed under good vacuum conditions 

 in Lamps 1 and 2. They are given by the values : 



a = 6'7 X 10 8 (amps, per sq. cm.), b = 54700. 

 Table I. 



Temperature. 



Thermionic Current. 



1050° K. 



0000000235 microamps. 



1100 



000000256 per 



1150 



0000227 sq. cm. 



1200 



0-000109 



1250 



000100 



1300 



0-00583 



1350 



0-0282 



1400 



0-122 



1450 



0-476 



1500 



1-70 



1550 



5-60 



1600 



17-1 



1G50 



490 



1700 



132- 



1750 



337' 



1800 



809- 



1850 



1880- 



1900 



4120- 



1950 



8730- 



2000 



17800- 



2050 



35200- 



2100 



67000- 



2150 



124000- 



2200 



224000- 



2250 



394000- 



2300 



674000- 



Lamp 3. 



Lamp 3 contained a filament 5*25 cm. long and a Copper- 

 gauze anode. It was given the usual treatment and sealed 

 off, but the seal cracked while cooling. The apparatus was- 

 then arranged so that the thermionic currents could be 

 measured with the lamp in place in the furnace, and connected 

 to the McLeod gauge, etc. After the lamp had been re- 

 heated and exhausted to a low pressure, the furnace was 

 opened, liquid air was applied at U and O, and a series of 

 observations was taken at once, beginning at low tempera- 

 tures. The potential difference was 190 volts. At several 

 points it was noticed that the current was unsteady, and that 

 it increased with the time. In these cases, readings were 

 taken every minute for 5 minutes or so, and the average 

 reading was taken. The pressure was " " at the beginning. 



