^^^ 



FlGUK 



K III. 







Fuurii 



■K IV. 



:l..-4- is Shown, 



or fi-a 



ire ], 



wliei'O an eqii 



i\ahMit 



meniscoid sliape 



1^ ,.iven. It is also evidon 

 ^'na.iged on either or both 



L that the k 

 surfaces of t 



Mitieular 

 he prisi 



power may be 

 n, provided the 



toful lell^rtl^ be 



uorrecl 



;. In 



other word^ 



thel-adii 





to satisfy the re 



■hitiou 











f 



= (u- 



-M'k-k- 



= 1- 





L.uU.oftke 



V^P^ o, 



i\,.<h 



,p,Ktaihs — 







Ihemxgnifji 



u- pov 



\(r ot 



th( se spe( tacles is liii 



Hted (unh^ss tlie 









) by the tact, 



that (h 



spersion of h-'ht 



aue to the prism 



xvouh 





3 coloured l)oi 



del s when the ULismatic 



m^les become e 



xte^sn 



e (in( 







• it IDIK us thlt 



ilinuJ.Yim"' 



-pect I 



";,';■' 



"notmtenda 



1 to .upp] 



IS .ho^ 



■ythfpLiceofa 

 vn bv a hst of 



iliJan^de^' "^ 

 ei, th« V possess 



^'■iH UM su.'hp, 





r ,n u 



M.r\n.4 .p. a 



l'!l. t,/ll 



Inon'nd'l^htul 



r the spect u 1. 

 nticulcir pou . . . 



in^tlJ:;;?^^' 



^p<. 



",",' 



-H.l 1. n^thy 



L.ilcuLxt! 



1^ '. 1.1 



d b> the follow 



"^'^ivi?:;;;! 



lo 



optKll p,IM 



;;;;::";,:'.,:':■; 



