hy Hot Plat'uuun in Air at Low Pressures, \)1 



activity iu scale-divisions per minute has been plotted against 

 the time the wire has been heated (in minutes). It will be 

 seen that there is practically nothing left after 5 minutes' 

 heating. 



Another case where '08 mm. of air was let into the appa- 

 ratus suddenly gave a higher rate of leak, viz. 382 divs. 

 per minute in the units which have so far been employed in 

 this paper. The actual readings and the times are given in 

 the followino- table : — 



+ ve Leak x . 



Time. 



154 



78 

 32 

 18 

 17 



min. sec. 



15 



1 15 



1 45 



2 30 



Here again it is evident that the induced activity is not very 

 persistent. 



The apparatus was now taken down and the wire allowed 

 to remain exposed to air at atmospheric pressure for several 

 days. On reducing the j^ressure to '001 mm. and keeping 

 the wire at -f 200 volts a leak of 160 divs. per minute w^as 

 obtained even when the wire was only heated with '228 amp. 

 The heating current was now raised to '240 ampere, and the 

 following values of the current were obtained at the „times 

 stated. The pressure was "0007 mm. 



4- ve Leak x . 



Time. 



255 



min. 

 



sec. 

 10 



19 



4 



15 



4 



8 



10 



o 



13 



10 



' t 



23 







In this case also there is practically no effect left after 

 heating the wire to a given high temperature for some five 

 or six minutes. 



