WPON THE DIFFERENTLY COLOURED RAYS OF LIGHT. 19 
15. Selenite. 
This mineral acts more powerfully upon green light than 
crown and flint glass, but less powerfully than ¢opaz. 
76. Spearmint, Oil of. 
This oil acts less powerfully upon green light than flint and 
crown glass, and oil of savine. - 
77. Spermaceti, Oil of: 
This oil acts more powerfully upon the green rays than flint- 
glass and oil of marjoram, and less powerfully than crown-glass. 
78. Sulphur. 
Sulphur produces a secondary spectrum when opposed to 
Jflint-glass and crown-glass, nearly as great as when oil of cassia 
is opposed to them. When it refracts in opposition to oil of 
. Cassia, no uncorrected colour is visible, but the oil appears 
to have a less action upon the green rays. 
79. Sulphuret of Carbon. 
This fluid acts much less powerfully upon the green rays 
than flint and crown glass, and all the essential oils except oil 
of cassia. 
Its action does not greatly exceed that of the oid of cassia. 
80. Super-sulphuretted Hydrogen. 
. This fluid has a more powerful action upon the green rays 
than flint and crown glass. When it refracts in Opposition to 
water, no uncorrected colour is visible, 
C2 81. Tartrate 
