( 387 ) 



sin"! + 2shfl{k,'' — n,') + (^/ + 71;)' = sin*Itg*I . . (27) 

 With metals iia'-^-ko' is comparatively large compared to the two 

 first terms of the first member of (27). By approximation we get 

 therefore : 



from which follows with the same degree of approximation 

 1 



SDl'I zr: 1 



Introducing this in (27), we get : 



1 2(^v-n/)- l 



4 K'+K^) 



sinltgl = Vk: + ^0' P + 7 M.. °.L • • • (28) 



In the following way we get an approximate value for H. From 

 (23) and (24) follows : 



ni — kf = 11^" — kg' z= sin" 1 -\- siii^ Itg^I coc 4 H, 

 SO 



n„^ — k'' — sin^J 



cos 4: H = 



sin^I tg I 



"^ CQs4 JJ 



From this follows, as tif2H = -—, tzt^, after substitution of the 



^ l-\-coséa 



approximate value 



sinUtgU= (n/ + ^-) j 1 + slnU^ff:^] 

 which follows from (27), 



tg2H=^lJ^sinU-^j-\ (29)^) 



11. Finally it may be observed that the relations hold for any 

 value of h. The reflection on perfectly transparent bodies is therefore 

 a limiting case for the metallic reflect ion. ") 



Chemistry. — ''On the chlorides of maleic acid and of fumaric 

 acid and on some of their derivatives!' By Dr. W. A. van 

 DoKP and Dr. G. C. A. van Dorp. 



(This communication will not be published in these Proceedings). 



1) Corresponding approximate formulae were given by Drude in Winkelmann, 

 Pliysik II. 1, p. 823, 824. 



2j Cf. VoiGT, Wied. Ann., 24, 146, 147, 1885. 

 (October 25, 1905). 



