494 



Ocv) neg. 



(«r) pos. 



Q 





/"pos. 



d1 

 -, pos. 



dr 



o 



Q 



EEPOBT 1887, 



Fig. 2. 



D 



A 



n 



u 



Q 



Q 



A 



b 



4 



C 



passim. 



passim. 



Here (mu) means an average of the kind described ia the footnote on (46) ; 

 e, e are rings which are being expanded ; 

 and c, c are rings which are being contracted. 



