250 



Mr. C. Spurge. On the Effect of Polish on the 

 Table IV. 





or. 



tan sr. 



L 





o 

 1 



ni .ft 



-02470 



107 °756° 





1 



25-7 



ft •0249^ 



107 "774 





1 



34 -2 



-02741 



107 '749 





1 



25-5 





107*972 





1 



24-4 



-02455 



107 -662 





1 



36-8 



-02816 



107 -687 





1 



27'4 



-02543 



107 -735 





1 



27 -2 



-02537 



107 -873 





1 



27 -8 



-02555 



107 -855 





1 



14*5 



-02168 



107 -953 





1 



20 -8 



-02349 



108-015 





1 



28-1 



-02565 



107 -805 



Means . . 



1 



26-5 



-02515 



107 '819 



Taking from Table III the mean values of R'— R, r'—r, we have — 



sin 86-769 



cos 2i 



sin 91-449 



0-99873. 



Thus ■w = 1° 26*6', and we obtain for the values of the quantities, 

 which we are seeking in order to determine the nature of the polarised 

 light, 



tan isr = 0-02520, 



I = 107*819 c 



Comparing these values with those formerly obtained which follow 

 Table II, we see that the effect of polishing is to cause a small 

 alteration of the ratio of the axes and in the inclination of the major 

 axis of the ellipse. Thus the ratio of the axes has been changed from 

 0*03346 to 0*02520, while the inclination has been changed from 

 108 088° to 107*819°, an alteration of about 16'. These results also 

 show that the reflected light is exceedingly nearly plane polarised. 

 Again, the Tables III give for the subsidiary quantity />, 



cos p = 



tan 86*769 



■0*44808, 



tan 91*449 



so that P = 116° 37'. 



The value of p obtained before polishing was — 

 P = 111° 14'. 



These values are not the same, but this has no bearing on the 

 polishing, inasmuch as p is a constant of the instrument and is inde- 

 pendent of the crystal. 



