328 F. E. Wright — Measurement of the Ojytlo Axial Angle 



Table 1. 





Observed 



Calculated 





Observed 



Calculated 



E 



Dv 



Dh 



Dv 



Db 



E 



Dv 



Db 



Dv 



Db 



0° 



















26° 



181 



186 





_ 



1 



8-5 



8 



. _ 



.... - 



7 



187-5 



192-5 











2 



16-5 



16 











s 



194-5 



199- 











3 



23 



22-5 











9 



199 



206-5 











4 



29 



30 











30° 



205-5 



212-5 



206-1 



211-2 



5 



36-5 



3 7 "5 



35-9 



36-8 



1 



213-5 



218-5 











G 



44 



44 









2 



219 



225 











7 



52 



51 











3 



225 



230-5 











8 



58-5 



57'5 











4 



230-5 



237'5 











9 



65 



65-5 







35 



236-5 



243-5 



236-5 



242-3 



10° 



71-5 



73-5 



71-6 



73-4 



6 



243 



250-5 











1 



78-5 



80 











7 



249 



256'5 











2 



85 



87-5 











8 



254 



261-5 











3 



92-5 



94-5 











9 



259 



266-5 











4 



100-5 



102 









40° 



264 



272 



265 



271-5 



15 



107-5 



109-5 



106-7 



109-3 



1 



269 



277 









8 



113-5 



117 









2 



273 



283 











7 



119-5 



124-5 











3 



279-5 



288 









8 



125-5 



131-5 











4 



286-5 



293-5 











9 



132 



138 







• 



45 



290 



299 



291-5 



298-7 



20° 



139-5 



144-5 



141-0 



144-5 



6 



295 



303-5 











1 



146-5 



152-5 











7 



300 



308 











2 



154 



1585 











8 



















3 



160 



164-5 











9 



. 













4 



166 



171 











50° 











316-6 



323-6 



25 



173 



179 



174-2 



178-5 













scale, K„ = 421-3 ; for the horizontal, K A = 422-4. The curves 

 of fig. 6 express these relations graphically, the zero line of each 

 succeeding curve being one division above the preceding curve, 

 to prevent confusion. For the objective in question (No. 9, 

 Fuess), and with the precautions observed to avoid parallax by 

 placing a fine stop diaphragm S (fig. 5) above the Ramsden 

 ocular, the agreement between theory and practice is remark- 

 able.* The screw of the horizontal (II, fig. 11, p. 336) micrometer 



*In tbe Mikroskopiscbe Pbysiograpbie I, 1, p. 330, by Eosenbuscb and 

 Wiilfing, tbe latter gives a series of measurements with an a-monobrom- 

 napbtbaline immersion objective of E. Winkel and finds disagreements 

 as high as 8° between observed and calculated values, as indicated in tbe 

 following table : 



H D K Hi 



Aragonite 11°83' 0'325 1-623 10°59 



Muscovite 24°43 0-700 1-674 24°14 



Topaz 39°05 1-075 1-705 (39°05) 



Calcite 60°51 1-590 1-821 68°50' 



The angles under H are half the axial angles for these minerals obtained 



