l4-4> M. Rudberg on the Refraction of the differently-coloured 



separate them in the manner already described for rock 

 crystal, 



... Prism Ay No. 1. — Refracting angle 30' 15' 29". Temp. 

 •fl9°. In the spectrum of greatest deviation, the ray F was 

 reduced to the minimum deviation, and in the other the ray H. 



Prism A, No. 2.— Refracting angle 42° 40' 16". 



The following were the indices observed in the spectrum 

 perpendicular to A. 



Prism A, No. 2. 

 1-63490 . 



Diff. 

 + 0-00016 

 —0-00017 



Prism A, No. 1 . 

 H . . 1-63506 

 G . . 1-63123 . . 1-63140 

 F . . 1-62652 

 E . . 1-62408 

 D . . 1-62109 

 C . . 1-61880 

 B . . 1-61791 

 And in the spectrum polarized parallel to A. 



Prism A, No. 1. Prism A, No. 2. Diff. 



H . . 1-62551 . . 1-62758 . . 0-00207 

 G . . 1-62156 . . 1-62374 . . 000010 

 Prism B.— Refracting angle 49° 3' 8". Temp. +19°. In 

 both spectra the ray H was brought to the minimum deviation. 

 Prism C— Refracting angle 38° 38' 54". Temp. 16°. In 

 both spectra the ray H was brought to a minimum devia- 

 tion. 



The following are the indices for the spectrum polarized 

 perpendicularly to the axes A, B and C. 



H 

 G 

 F 

 E 

 D 

 C 

 B 



A. 

 1-63506 

 1-63123 

 1-62652 

 1-62408 

 1-62109 

 1-61880 

 1-61791 



B. 



1-62539 

 1-62154 

 1-61701 

 1-61452 

 1-61161 

 1-60935 

 1-60840 



C. 



1-62745 

 1-62365 

 1-61914 

 1-61668 

 1-61375 

 1-61144 

 1-61049 



n n 

 And the ratios -77-, —^ will be as follows ; 



n" 



Ratio 



H 

 G 

 F 

 E 

 D 

 C 

 B 



1-00466 

 1-00467 

 1-00456 

 1-00458 

 1-00455 

 1-00459 

 1-004.61 



Ratio '-sTT 

 11'" 



1-00595 



1-00597 



1-00588 



1-00592 



1-00588 



1-00587 



1-00591 



