UPON THE DIFFERENTLY COLOURED RAYS OF LIGHT. li 
It acts very little more powerfully than the balsam of 
Tolu. 
31. Cassia, Oil of: 
Oil of Cassia acts less powerfully upon green light than sul- 
phur, balsam of Tolu, and every other substance with which I 
have compared it. With sulphur the uncorrected colour is just 
visible. 
When acting in opposition to sulphuric acid, it forms a se- 
condary spectrum of a very large size; these substances being 
at the opposite extremities of the scale. 
32. Castor Oil. 
Castor Oil acts less powerfully upon green light than crown- 
glass. : 
It acts a very little less powerfully upon green light than 
Juni-glass. 
33. Chamomile, Oil of. 
This oil acts less powerfully upon green light than crown- 
glass. 
It acts a little less powerfully upon green light than flint- 
glass. 
34. Cloves, Oil of. 
Oil of Cloves acts less powerfully upon the green rays than 
oil of lavender, Canada balsam, and flint-glass. 
_It acts more powerfully upon the green rays than oid of sas- 
safras, and oil of cummin. 
B2 35. Copal, 
