UPON THE DIFFERENTLY COLOURED RAYS OF LIGHT. [7 
; 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 witha 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 Jlint-glass, and is a 
little less than that of calcareous spar. — 
rarity wy 68. Rock-Crystal. 
This intents acts more powerfully upon green Awe than 
_Jlint-glass, crown-glass, and muriatic acid. 
Vor. VIII. P. I. Cc It 
