UPON THE DIFFER-ENTLY COLOURED RAYS OF LIGHT. If 



64. Poppy , Oil of. 



This oil acts less powerfully upon green light than either 

 flint or crown glass. 



65. Rape-seed, Oil of. 



This oil acts less powerfully upon the green rays than crown- 

 glass, and a very little more powerfully than flint-glass. 



66. Rhodium, Oil of. 



This oil acts less powerfully upon green light than crown- 

 glass, and more powerfully than oil of cloves. 



When a prism of oil of rhodium with a great refracting angle, 

 was opposed to a prism of flint-glass with a small angle, the 

 green fringe appeared towards the vertex of the flint-glass 

 prism. 



When a prism of oil of rhodium with a small refracting 

 angle, was made to correct a prism of flint-glass with a large 

 angle, the uncorrected green appeared towards the vertex of 

 the oil of rhodium. Hence we may infer that these two bo- 

 dies exercise the same action upon the green rays. 



67. Rock-Salt. 



This substance exercises a much greater action upon green 

 light than rosin. 



It exercises a less action upon the green rays than crown- 

 glass. Its action exceeds a little that of flint-glass, and is a 

 little less than that of calcareous spar. 



68. Rock-Crystal. 



This mineral acts more powerfully upon green light than 

 flint-glass, crown-glass, and muriatic acid. 



Vol. VIII. P. I. C It 



