UPON THE DIFFERENTLY COLOURED RAYS OF LIGHT. 19 



75. Selenite. 



This mineral acts more powerfully upon green light than 

 crown and Jlint glass, but less powerfully than topaz. 



76. Spearmint, Oil of. 



This oil acts less powerfully upon green light than flint and 

 crown glass, and oil qfsavine. - 



77. Spermaceti, Oil of. 



This oil acts more powerfully upon the green rays than jlint- 

 glass and oil of marjoram, and less powerfully than crown-glass. 



78. Sulphur. 



Sulphur produces a secondary spectrum when opposed to 

 flint-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 oil 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 



