972 Mr. M. Siegbahn on the Study of Variable 



we are in possession of the means necessary for the deter- 

 mination of the e- and /-values. According to the additional 

 theorem 



e »/,(*) +/,(£), 



(3) 



or 



E-/,(i) =/„(«) (4) 



This alteration of oar formula gives as a simple method of 

 graphically finding the e- and /-value. 



From the line e=E, J\(j) is sel off : its intersection with 

 f 2 (i) is the required point of equilibrium A. 



From this Kauffmann's conditions of stability are easily 

 found. From (3) is obtained by differentiation with respect 

 to the strength of current (/), 



f i / j d/ L of* 



Oi Oi 



(5) 



for a stable equilibrium, it is reqnired that this expression 

 shall be greater than the given voltage E ; or 



(6) 



(') 

 (8) 



stable : 



\ fi + 1& > 



o* Ol 



indifferent : 



di o* 



unstable : 



M + M<0. 



0« Oi 



,. M 



Graphically :— signifies the angular coefficient of the 

 tangent at the point in question. 



