( 742 ) 

 § 3 ; the total electric force produced by it is given by 



if we distinguish by the index J the quantities corresponding to the 

 second plane wave for which OP is the direction of the ray. The 

 magnetic force too has in both cases the ordinary direction and may 

 be derived from the electric force by multiplying respectively by 



C C cos &„ C C cos ■Ö', 



so that the flow of energy is given by 



or 



n" c' b»,/, t' p, p', cos' », 2a f r\ 



-I '^ ^^-^ -' cos^ — t I . 



^ T*F/ 2'V pj 



The mean flow of energy per unit time is therefore 



71' c'r bV„T'p„p'„ cos' -^^ t> V„ t' p. p>os' J», 1 

 2T*\_ F„' "^ F,' J' 



The amount of energy travelling outwards in directions lying 

 within the cone of rays do' , is 



r' ® do. 

 We may finally observe that the cone of corresponding wave- 

 normals has a solid angle 



do =: Q q' cos' & . r" do' 

 so that the total amount of energy radiating from the centre may 

 be represented by the integral 



2T*J\V^.' ^ F/ J 

 It is only in the case of uniaxial crystals that this integral can 

 be further calculated. 



Geology. — "On brackish and fresh ïoater deposits of the river Silat 

 in Western-Borneo." By Prof. K. Martin. 



(This communication will not be published in these Proceedings). 



(March 22, 1906). 



