444 EXPLANATION OF PLATE XXVII. 



Blue, and, last of all, the Indigo; so tliat the combinations of Blue 

 glasses have now the effect of Red glasses. 

 No. 5. Shews the effect of increasing the Blvc glasses in No. 4. to a certain 



thickness. 

 No. 6. Shews the effect of a Sly-lluc paste, whicli reflects most copiously the 

 Blue light. The whole spectrum is destroyed excepting the extreme Bed. 

 No. 7. Represents the effect produced by a great thickness of Green glass. 

 No. 8. Sulpliate of copper, which is bluish-green, both in the solid state and in 

 the state of a solution, leaves unabsorbcd a great quantity of Yellow 

 lio-ht, which may be rendered tolerably homogeneous by means of a 

 pale Yellow glass. The figure shews its effect in attacking the Red and 

 Violet ends of the spectrum, a portion of blue and red being left. 

 No. 9- Shews the effect of a greater thickness of Sulphate of copper, in absorbing 

 all the Red, and leaving a Greemsli-t/cUou', with an adhering margin of 

 blue light. 

 No. 10. Shews the influence of a thick plate of Yelhwisli-red glass, in absorbing 



all the blue, and part of the green, leaving the violet slightly affected. 

 No. 11. Represents the singular effect produced by a solution of Lake. Ther* 

 are here two greens, and an effect is produced at the boundary of the 

 red and green space. 

 No. 12. Represents the effect of a thick piece of fine Red glass, coloured with gold, 

 and also of a piece of stained glass, which I found in the Abbey of 

 Konigsfelden, in the canton of Berne. The same effect is produced by 

 common red ink, and by a solution of beet-root in vinegar. 

 No. 13. Shews the action of an opaline milky-white glass upon the most refran- 

 gible half of the spectrum. 

 No. 14. Shews the effect of a certain thickness of native yellow orpiment. 

 No. 15. Shews the effect of a red glass combined with yellowish-green and bluish- 

 green glasses. The yellow is much more copious and brilliant when 

 the red glass is combined with a certain thickness of sulphate of cop- 

 per, but it is then fringed vnth a narrow margin of Red on one side, 

 and of Green on the other. 

 No. 16. By combining with the same red glass a thicker plate of sidphate of cop- 

 per, the yelloto becomes green ; and by a, thicker plate still, the coloiu- 

 becomes blue, as in the figure. 



XXXL 



