﻿216 



Mr. J. A. Brown on the Potential required 



is increased as far as the values were taken. In general, the 

 curves were not pushed on beyond the values given, but 

 Curve 5, fig. 10 (see below), with aluminium plates shows 

 that carrying the current to greater values would not intro- 

 duce any change in the above generalization. 



For pressures below the critical pressure, however, the 

 case is quite different. Curve A, fig. 4, is practically at the 



Fig. 4. 



1/OLTS 









Vo 



LTS 















A 







500 







c 







275. 



Sp 



17=270 







475 



Sp. 



17=37* 









Z5Q . 







p=/J 





450 

















 (xl-4-x 



i i 

 \0~ 5 = /\f 



1 



nps.) 



5 



4?5 













l/OL7 „ 



325 - 



Sp.V^ 



B 



281 







400 







p^0.5 



3 





300 











375 













275 





J" 6 



.77 





350 













5 10 15 



(xl4x 10-5 ^Amps.) 



5 10 15 BO 25> 



fxl4x 10 " 5 = Amps) 



Below the Critical Pressure. 



minimum sparking potential. Here there is a slight drop 

 from the sparking potential to the potential required to 

 maintain the current ; but it soon rises until it passes the 

 sparking potential and remains above it as far as the investi- 

 gation was carried. At lower pressures this is still more 

 easily seen. Curves B and C (fig. 4) show absolutely no 

 drop ; the curve at first increases very rapidly from the 

 direction of the sparking potential, and gradually seems to 

 approach a limit. 



These curves are all the average of a large number of sets, 

 which sometimes differ considerably in their values, so that 

 undue emphasis must not be put on the absolute values. A 

 sufficient number were taken, however, to ensure a fair degree 



