612 Miss P. M. Borthwick on Potential Measurements in 



the field at the surface of the point under the same conditions, 

 and proves conclusively that although the minimum dis- 

 charging potential between a point and a plane depends on 

 the distance between the electrodes, the potential drop in the 

 neighbourhood of the point does not. 



The readings, for any given value of x, of the potential 

 drop (V) for different currents (C) are interesting, and are 

 shown in Curves II., which include V, C curves for different 







Curves II. 



vac* 





___^— *^~~~~~ \J *>3">nmf 



k* 









-0- O — r 



? tr 





^ • *"" U = 2. -mm?. 



—° O--- o o--— -o 





— 0—0-- ■ --J^o~rr--~-~o77. _ 





r-« ° 



,, -e 



%S 



« -"* — * V = / Tntn. 





0- - -0~$»— tF* - O- — - - '- -St - 



-■-o -p- o- -o~--~ o ] **"' 



1 



-4r£d—0—O:-r-—O—* 



rrgrr=fc£ , d ! ~"-'-' ■ "S-^—e- — ©-*. — -Oy. Q'S"-rran 



e 



' J 



■ ' ,U ' ' ' ' /.V McToatofxrea 



distances (V) between the point P and the explorer E, and for 

 both positive (full lines) and negative (broken lines) discharge 

 from P.. (N-B. The curves for y = 2 mm. and y — 3 mm. are 

 displaced along the V axis for convenience, the ordinates 

 having been multiplied by 1*25 and 1*5 respectively.) It will 

 be seen that for a given value of y, V is practically constant 

 for all currents for a negative point; for a positive point, 

 except for the smallest value of y, V increases with increase 

 in current. 



Now when the current is passing, Y is complex in cha- 

 racter, being made up of the potential drop at the point 

 (anode or cathode as it may be), the potential drop in 

 the glow, and that in the space between the glow and E. 



surprising that V changes with 



change decreases as y decreases, 



y=0'5 mm. show that, at the 



This being so, it is not 

 current. But the rate of 

 and readings taken with 



ihortest distance of E from P, the variation with current 



