988 Sir J. J. Thomson on a 



The distance between two maxima is 27r/&, or, approximately r 



so that, unless the value o£ Ej differed from that of E by 

 less than 1 per cent., the distance between the maxima would 

 be several millimetres. This distance is of the order indicated 

 by experiments. 



The striations we have considered hitherto have been those 

 on a background of continuous luminosity, the variations in 

 E being so small that E nowhere fell below the value E 

 necessary for ionization. If the pressure is so small that we 



may neglect the term %1-j— in equation (7), we can proceed 



a step in its integration and obtain further insight into the 

 variations of E. Let us suppose that we follow the electrons 

 from a place in the negative glow where both E and X 

 vanish ; by equation (6) d~E/dx will also vanish. As long as 

 E is less than E , q vanishes and equation (7) becomes 



dx 2 \e V2E7^j' 



of which the solution when both E and dE/dx vanish when 

 ;e=0 is 



-(•S=) v (15 > 



This holds until E = E ; for larger valtfes of E the 

 equation is 



d 2 E __ 2 / i qe\ 



d^~^ e \ e V2Wi W ; 

 or, if q = icp(E-'E ), 



S-Mdipr'f< E - E 4 



a first integral of this is 



i/^y =4 ^ 2 /j^_i-P (E _ Eo)2 \ 



2\dxJ KeV'Zlm 2 £ K °' J 



This satisfies the condition that when E = E , the value of 

 dE/dx given by this expression is the same as that given 

 by equation (15). The maximum value of E is therefore 

 given by 



1 ^(E-E„) 2 . . . . (16*) 



(16) 



e V2jm 2 /3 



