Discharge of Electricity through Gases. 701 



On reducing the pressure to O04 mm. (Table XIV.) the 

 potential-gradient becomes so steep that only the German 

 voltmeter was available for measuring the cathode-fall, and 

 even it was working at a very unsensitive part of its scale. 

 The electrode D was right in the middle of the negative 

 glow, and the whole of the rest of the tube was practically 

 dark. But as soon as the cathode became white-hot the 

 pressure began to rise so much that the measurements on 

 cooling down were not strictly comparable. 



The most interesting part, however, of this table is that 

 which shows the effect of variations of current on the 

 potential-gradient in different parts of the discharge. For 

 all values of the current greater than about 2*5 X 10~ 4 amperes 

 the potential-difference across the whole 83*5 mm. (D — A) 

 at the positive end of the discharge remained too small to be 

 measured by any of the available instruments ; and, as has 









Table XT 













A = Cathode ; K = Anode. 



1 



Temp, of 

 Anode. 



i i ! 



Potential Difference. Current. Pressure 





1 mm r\£ 



Dedn. 



°C. i 



A-K.j A-B. 



B-D. A "; D w"i K v Defln. 

 (calc.) (calc.) 



Amps.! Hg. [ 



xio\ 



1-8 



70 



875 352 



255 607 



268 



242 



8-07 





! T8 70 



850 366 



214 580 



270 



24-5 



817 





- 



1 



370 



210 580 





24-9 



8-30 







850 ■ 366 



231 597 



253 



24-3 



8-10 





• 155 



438 



780 | 367 



194 561 



229 



242 



8-07 



1-83 j 



17-4 



482 



775 368 



194 562 



213 







18-1 



498 



775 368 



198 566 ! 



209 



241 



8-03 ! 



17-9 492 



775 370 



192 562 



213 



240 



8-00 



44-8 1060 



770 i 370 



202 572 



198 



239 



797 



504 



1167 



770 : 369 



208 577 



193 



236 



7'87 



60-3 



1340 



768 367 



213 580 



188 







7V4 



1533 



765 365 



220 5*5 



180 



226 



7-53 





71-4 



1533 



768 358 



230 588 



180 



236 



7-80 





71-4 



1533 



765 362 



217 579 



186 



241 



8-03 





77-5 



1635 



765 362 



225 : 5 7 



178 23 95 



7-98 





i 82-4 



1710 



770 370 



232 602 



168 23-2 



773 









1 370 



224 594 



... 245 



8-17 





83 



17-25 



375 



220 595 



251 



8-37 





634 



1397 



793 381 1 



208 588 



2()5 249 



830 





514 1185 



793 ', 383 



198 581 



212 249 



830 





19-4 525 



793 



190 573 



220 246 



8-20 





176 485 



800 383 



187 570 230 245 



547 





24 91 



383 



220 603 



23-5 



7-83 





2-4 91 



845 



297 590 



255 24-8 



8-27 





2-3 89 



810 



166 551 259 345 



11-50 







810 383 



1 



160 543 267 41-7 



1390 1-82 



