C. S. Hastings — Double Refraction in Iceland Spar. 69 



II contains all the measures for the ordinary ray, then the tem- 

 perature (t), the barometric height (Bar.), and the angle cor- 

 rected to 30 inches barometric height. In the table, the mis- 

 takes mentioned, and which were confined to the four preced- 

 ing the last, are corrected by adding /# 285, the measured dis- 

 tance between D 1 and D 2 . 



Table II.— Double angles of deviation for ordinary ray D 2 . 



2A = 104° 





PQ 







PR 









QR 







Obs. 



t 



20-3 



Bar. 



Cor. 



Obs. 



t 



Bar. 



Cor. 



Obs. 



t 



16-7 



Bar. 

 30-1 



Cor. 



+ 8 A 454 



29-85 



+ 8'-423 



-3'-772 



19-4 



30 



1 



-3'-752 



+ 7 -658 



+r 



678 



•472 



20-4 



29-85 



•441 



•701 



19-8 



30 



1 



•681 



•546 



17-1 



30-1 





566 



•497 



20-7 



29-85 



•466 



■661 



19-9 



30 



1 



•641 



•531 



17-2 



30-1 





551 











•559 



20-3 



30 



1 



•539 



•336 



17-9 



30-1 





356 











•560 



20-2 



30 



1 



•540 



•134 



18-8 



30-1 





154 











•552 



206 



30 



1 



•532 



+ 7'-085 



19-0 



30-1 





105 











•618 



19-8 



29 



75 



•669 



+ 6'-983 



19-1 



30-1 



+ 7' 



003 











•479 



20-3 



29 



75 



•530 



■921 



19-7 



30-1 



+ 6' 



941 











— 3'-455 



20-4 



29-75 



-3'-506 



■914 

 •799 

 •839 

 •743 



20-1 

 20-1 

 20-2 

 206 



30-1 

 30-1 

 30-1 

 30-1 





934 

 819 

 859 

 700 



















+ 6 A 680 20-6 



30-1 



+ 6'-762 



The observations for PR and QR were reduced by form- 

 ing observation equations of the type 



M = m+n(t— 20). 



and, the temperature correction for PQ being assumed as the 

 same as that for PR, the reduced values for J are, for 



PQ 4' 10 /r -20±0 // -54-f6"-'72(£-20) 



] l"-52 ± 0"'18-J-6 -72(« — 20) 

 26 // -10±0"'30— l"-11(t-20) 



Table III. 



2A = 



PR 

 QR 



51° 



52° 



58' 

 3' 



PQ 94° 



PR 94° 



QR 72° 



Obs. 



t 

 20-7 



Bar. 



Cor. 



Obs. 



t 

 19-6 



Bar. 

 30-1 



Cor. 



Obs. 



t 



16-8 



Bar. 

 30-1 



Cor. 



+ 7'-983 



29-85 



+ 7 / -955 



-2'-518 



-2'-537 



+ 3'-474 



+ 3 A 489 



8 A 045 



20-7 



29-85 



8 A 017 



•555 



19-7 



30-1 



•574 



•454 



16-9 



30-1 



•469 



•101 



20-8 



29-85 



•073 



•454 



19-9 



30-1 



•472 



•456 



17-4 



30-1 



•471 



•110 



20-9 



29-85 



•082 



•430 



19-9 



30-1 



•448 



•360 



17-7 



30-1 



•375 



+ 8'-088 



21-0 



29-85 



+ 8'-060 



•436 



20-5 



301 



•454 



•356 



18-9 



30-1 



•371 











•391 



20-6 



30-1 



•409 



•307 



190 



30-1 



•322 











•429 



20-0 



2975 



•475 



•331 



19-2 



30-1 



■346 











-2'-361 



20-1 



29-75 



— 2 A 407 



•309 

 [3'"495] 

 •294 

 •277 

 •251 

 [3'-634] 



19-4 



20-1 

 20-4 

 20-5 

 20-6 

 20-6 



30-1 

 30-1 

 30-1 

 30-1 

 30-1 

 30-1 



•324 



•309 



•392 



+ 3'-266 



