UPON THE DIFFERENTLY COLOURED RAYS OF LIGHT. 11 



It acts very little more powerfully than the balsam of 

 Tolu. 



31. Cassia, Oil of. 



Oil qf 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 

 flint-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 oil of sas- 

 safras, and oil of cummin. 



B 2 35. Copal, 



