Bays of Great Wave-length in Rock-salt, Sylvite, 8fc. 41 



Table I. 

 Refracting Angle of the Rock-salt Prism, (£=60° 2\ 





K = 8*307/i; 



% is 11th Order. 



Name. 



a. 



n. 



\. 





42 37 



41 56 



7 



40 47 



29 



1-5607 

 1-5531 

 1-5441 

 1-5404 

 1-5370 

 1-5358 

 1-5347 

 1-5337 

 15329 

 1-5321 

 1-5313 

 1-5305 

 1-5299 

 1-5293 

 1-5286 

 1-5280 

 1-5275 

 1-5270 

 1-5264 

 1-5257 

 1-5247 

 1-5239 

 1-5230 

 1-5217 

 1-5208 

 1-5197 

 1-5184 

 1-5163 

 1-5138 



fi. 



0-434 

 0-485 



0-589 

 0-656 

 0-755 

 0-790 

 0-831 

 0-876 

 0-923 

 0-978 

 1-035 

 1-107 

 1-186 

 1-277 

 1-384 

 1-511 

 1-660 

 1-845 

 2-076 

 2-372 

 2-771 

 3-022 

 3-320 

 3-690 

 4150 

 4-745 

 5-540 

 6-647 

 8-307 



F 



D 



° 



a, 



b :.::: 



22^ 

 16* 



U* 



7 



39 58 



54* 



51 

 47i 

 44 

 41 

 38 

 35 

 32 

 28 

 22| 

 18 

 18* 

 7 

 2 

 38 56 . 

 49 

 37^ 

 24 



« ., 



bi 





5 :::;::::::::::: 



b ± 



a 



b 





bi ::::::::::::::: 



a^ 



& 7 7 ::: ::. 



« u 



&„ 



Ct n 



c, 



b Q 



C 2 ■•- 



a-, n 



c„ 



*io ■ 



c, 



a-,, 





It is well known that Professor Langley*, by a method 

 wholly different from the one here described, was able to 

 follow the dispersion in rock-salt to a wave-length \ = b'ofjb. 

 He found, in these experiments, that the curve of dispersion 

 from about \=2fi on followed very nearly a straight line. 

 Owing to the fact that even with the elaborate means at 

 hand he was unable to extend measurements by his method 

 farther than this in the direction of the long wave-lengths, lie 

 concluded to extend this straight line throughout the still 

 more distant region of the infra-red in which his observations 

 were taken. 



Many theoretical objections are at once suggested by so 

 extensive an exterpolation. Among these criticisms may be 



* Ann, de Chim. et de Phys. [6] ix. p. 433 (1886). 



