Ionizing Processes at a Paint discharging in Air. 281 



The maximum value of f Q just before each spark passed is 

 given by the dotted line in Curves I. for g = 0fl5 cm. 



An interesting detail was noticed in connexion with the 

 position of the glow on P in the first set of experiments. 

 Here N was on one sioje of P and the glow always appeared 

 on the side facing J^, but becarne symmetrical when N was 

 removed. This is consistent with what was said above, as 

 ionization in the reduced fields of case b can oqly occur when 

 the external ions approach the point. A negative pqint, qn 

 the other hand, only glows in case c, and it can then 

 discharge whether external ions are arriving or not ; this 

 agrees with the fact that the positiqn of the negative glow 

 was far less dependent upon the position of N than that qf 

 the positive. 



Negative Discharge from P. 



Here, as with positive discharge, the curves consist of two 

 distinct portions, S and H, corresponding respectively to 

 dark and luminous discharge. Of these S, as before, repre- 

 sents case a, and if for a moment we neglect the curve for 

 ^ = 1*0, H in every case appears to correspond with case c, 

 as it should, the qrdinates of the various H curves down 

 to ?/ = l*5 being roughly the same as those for no discharge 

 from N (j/ = co ). 



For t/ = 0*5 and 0*3 the curves were cut off short by the 

 passage of sparks between N and P, but there seems no 

 reason to suppose that if their H portions had been obtainable 

 they would have differed in position from the others for 

 normal point discharge. 



In the case of y = 0*3 the curve is shown forking. The 

 reading at the top of the lower branch was taken just before 

 a single spark passed, while that for the upper branch 

 corresponded with a stream of sparks. The ordinate of the 

 latter was therefore multiplied by v 3, as explained above, 

 and this has brought it well among the rest of the H curves. 

 The dotted lines correspond with the discharge of streams of 

 sparks as before. 



Between y = 0'3 and ?/ = 015 there appears tq he a funda- 

 mental change in the character of the discharge. The 

 ordinates of ?/ = 0'15 have been multiplied by -y/3, but this 

 has not brought them anywhere near the top of z/ = 0'3. 



It is possible that in the curve for y=l'0 we have the 

 transition stage connecting ^ = 03 and ^ = 015. In normal 

 point discharge the glow is confined to the region near the 



Phil Mag. S. 6. Vol. 20. No. 116. Aug. 1910. U 



