Prof. Owens on Thorium Radiation. 



379 



only were used, and are given in pounds per square inch. 

 The current at atmospheric pressure in each case is taken 

 as 100. An inspection of the curves at once shows that as 

 the distance between the plates is diminished, a greater and 

 greater pressure must be used before the current begins to 



Table VII. 



Thorium Oxide. Thick layer. 



Conduction-current with Pressure. 



Plates 1 cm. apart. Lower plate 95 volts + , 



Pressure in mm. Hg. 



Time of 100 div. in see. 



Current. 



60 



134-0 



160 



105 



1110 



200 



155 



53-0 



410 



305 



29-0 



760 



455 



22-4 



98-0 



630 



21-6 



1020 



760 



22-0 



1000 



1266 



320 



69-0 



1813 



42-0 



52-0 



2280 



54-5 



40-0 



2786 



74-0 



300 



i 



D 



Fig. 9. — Conduction-current with Pressure. 

 Thorium Oxide. Thick layer. Plates 1 cm. apart. 



10 12 U 16 18 20 



Pressure in 100 mm. of mercury. 



26 



