1862.] 169 



The cotangent of the azimuth of incident polarization is called 

 the Coefficient of Reflexion, and upon it appears to depend the rich 

 lustre, strikingly exhibited in polished copper and gold. 



The paper contains an account of the experiments made to deter- 

 mine, with precision, these constants for the following substances ; 



A. Transparent Bodies. 



1. Munich glass (a). 4. Fluor-spar. 



2. Munich glass (*). 5. Glass of antimony. 



3. Paris glass. 6. Quartz crystal. 



B. Pure Metals. 



1. Silver. 7. Zinc. 



2. Gold. 8. Lead. 



3. Mercury. 9. Bismuth. 



4. Platinum. 10. Tin. 



5. Palladium. 11. Iron and steeL 



6. Copper. 12. Aluminium. 



C. Alloys. 



1. Copper and tin (speculum metal). 9. Copper and zinc (3 Cu+Zn). 



2. Copper and zinc (10 Cu+Zn). 10. (2 Cu+Zn). 



3. (9 Cu+Zn). 11. (Cu+Zn). 



(8 Cu+Zn). 12. (Cu+2Zn). 



(7 Cu+Zn). 13. (Cu+3Zn). 



(6 Cu+Zn). 14. (Cu+4Zn). 



(5 Cu+Zn). 15. (Cu+5Zn). 



(4 Cu+Zn). 



The determination of the optical constants of these substances 

 leads to many interesting conclusions ; among which the following 

 may be stated : 



1 . That transparent bodies, as well as metals, possess a coefficient 

 of reflexion, which is sometimes very sensible, although there are 

 bodies in which it is very small. 



2. That Silver is the only substance which possesses the qualities 

 of brilliancy and lustre, represented by the coefficients of refraction 

 and reflexion, in a high degree. 



3. Of the metals which have high brilliancy and little lustre may 

 be named Mercury, Palladium, Zinc, and Iron. 



4. Of the metals which have high lustre and little brilliancy 

 there are only two, Gold and Copper. 



5. Results of the highest interest appear from an examination of 



