UPON -THE DIFFERENTLY COLOURED RAYS OF. LIGHT. 13 
40. Ether. 
Ether seems to have the same action upon green light as ai- 
cohol. 
41. Fennel-seeds, Sweet, Oil of. 
This oil acts much less powerfully upon green light than 
junt and crown. glass, and.less powerfully than oi! of dill 
seed. 
42, Fenugreek, Oil of. 
This oil acts less powerfully upon green light than flin¢ and - 
crawn glass. 
43. Fluor-Spar. 
Fluor-Spar acts less powerfully upon green light than sulphu- 
ric acid, and the white of an egg. 
44. Glass, Crown. 
Crown-glass acts more-powerfully upon green light than 
fint-glass, oil of spermaceti, oil of olives, oil of ambergris, copal, 
or oil of juniper. 
It acts less powerfully upon green light than gum Arabic, al- 
cohol, topaz, fluor-spar, the acids, rock-crystal, and water. . 
45. Glass, Flint. 
Flint-glass acts less powerfully upow green light than oil of 
spermaceti, oil of olives, oil of ambergris, essential a of juniper, 
oil of rape-seeds crown-glass, &c. 
It acts more powerfully upon green light than Canada bal- 
sam, and almost all the essential oils, excepting those ey 
mentioned, 
When. . 
