698 



Mr. J. A. Cunningham on the 



have become less marked though still apparent. The differ- 

 ence o£ potential between the cathode and the top of the 

 positive column (K — D) shows a distinct tendency to a 

 maximum above 1500° C. The potential-gradient in the 

 positive column (D — B) is pretty nearly constant with a 

 slight minimum about 920°, after which it increases uniformly 

 up to the highest temperature attained. The curves for 

 heating up and cooling down are indicated by the arrows, 

 cooling curves being dotted. 



In Table XII. and fig. 6 the pressure is still further reduced 

 to 0'4 mm. The initial minimum and maximum of potential- 

 difference at the negative end of the discharge have broadened 

 out, so to speak, along the axis of temperature, and contracted 

 parallel to the axis of potential. There is a gentle maximum 

 about 800° C, and a second above 1500° G. before the final 

 very rapid diminution. 



Table XIII. and fig. 7 : — In this series of experiments, 

 made soon after admitting a fresh supply of air, so far from 

 the apparatus showing any tendency to leak, the pressure 

 steadily diminished during the course of the experiments. 

 This could only be accounted for as being due to the constant 



Table XIII. 



Temp, of 

 Cathode. 



Potential Diff 



erence. 





Current. 



Pressure, 





1 







K-B. 







mm. of 

 Hg. 



Defln.! °C. 



1 

 iJv-A. 



• 



540 



K-E. 



E-A. 



187 



K-D. 



i Defln. 



Amp. 



xio 5 . 



1-9 



74 



355 



430 



510 



J 29-0 



1740 



0-172 



20-5 



550 



580 



410 



185 



490 



560 



321 



1922 



0173 



286 



732 



600 



429 



178 



510 



587 



332 



19 92 



0-171 



33-5 



837 



! 615 



453 



177 



530 



602 



356 



21-36 



0167 



49-7 



1153 



640 



474 



172 



552 



623 



1 ... 



... 



0-167 



60-9 1 1350 



I 670 



515 



169 



586 



654 



41-1 



24-66 



0-156 i 



69-5 



1500 



! 710 



542 



169 













70-5 



1518 



! 705 



(530) 



173 



620 





42-7 



25-62 





716 



1536 



710 



(546) 



164 



640 











72-6 



1552 



710 



(549) 



161 



641 











73-3 



1566 



t 710 



(549) 



161 



630 





i 45-0 



27'00 





73-8 



1574 



! 705 



(550) 



155 



615 











74-2 



1580 



'< 700 

 665 



(546) 

 (515) 



154 

 150 



598 

 560 





... 





0-150 







655 



(502) 



153 



565 











71-0 



1526 



740 



(583) 



157 



660 











75-0 



1593 



700 



(546) 



154 



624 











761 



1612 



680 



(528) 



152 



600 











76-7 



1620 



670 



(520) 



150 



590 











74-5 



1585 



740 



(585) 



155 



655 











72-0 



1540 



760 



605 



155 



670 











67 "5 



1468 









670 











57-2 



1290 



' 755 



598 



157 



660 











1 



740 



583 



157 



655 











38-5 i 937 



720 



562 



158 



637 





' 







5*5 



188 



670 



514 



156 



573 





'; 57 6 



34-56 



0140 



