‘UPON: THE DIFFERENTLY COLOURED RAYS OF LIGHT. ‘9 
It acts more powerfully upon green light than oil of cas- 
sid. 
20. Arabic, Gum. 
Gum Arabic acts more powerfully upon green light than oi 
of cassia, balsam of Tolu, and flint-glass. 
When it opposes crown-glass, the uncorrected colour is 
scarcely perceptible ; the excess of action on green light being 
on the side of the gum. 
It acts less powerfully upon green light than ¢opaz and rock- 
crystal. : 
21. Beech Nut, Oil of. 
This oil acts less powerfully on green light than crown- 
glass. 
_ It acts a very little less powerfully upon green light than 
Slnt-glass. 
22. Bergamot, Oil of. 
This oil acts less powerfully upon green light than flint and 
crown glass. 
No uncorrected colour is visible when it acts in opposition 
to oil of marjoram. 
23. Beryl. 
Beryl acts more powerfully upon green light than Jlint and 
crown glass. 
24. Borax. 
Borax acts more powerfully upon green light than flint and 
trown glass. 
Vou. VIL PL B ‘25. ies 
