14 ON THE ACTION OF TRANSPARENT BODIES 
When flint-glass acts in opposition to balsam of Capivi, nut 
oil, oil of rhodium, and oil of rosemary, no secondary spectrum is 
~visible. 
46. Glass, Opal-coloured. 
This glass acts more powerfully upon green light than oil of 
cassia, and balsam of Tolu. 
It acts less powerfully upon green light than flint-glass. 
47. Giass, Orange-coloured. 
This glass acts less powerfully upon green light than crown- 
glass, and very little less than flint-glass. 
It acts more powerfully upon green light than oil of amber, 
and oil of anise-seeds. 
48. Glass, Red-coloured. 
This glass acts less powerfully upon green light than flint 
nd crown glass. 
49. Hyssop, Oil of. 
This oil acts less powerfully upon green light than crown- 
glass, and a little less powerfully than flint-glass, and oil of pep- 
permint. 
50. Ice. 
When ice is opposed to flint-glass, it forms a secondary spec- 
trum, having the same position, and nearly the same magni- 
tude, as when water is combined with flint-glass. 
51. Juniper, Gum. 
This gum acts less powerfully upon green light than crown- 
glass. 
52. Juniper, 
