UPON THE DIFFERENTLY COLOURED RAYS OF LIGHT. QF 
87. Water. 
Water acts more powerfully upon the green rays thar flint 
and crown glass, rock-crystal, the white of an egg, and the great-. 
er number of the acids. It acts less powerfully, however, than 
the phosphorous, sulphurous, phosphoric and sulphuric acids. 
88. Wormwood, Oil of. 
This oil exceeds flint and crown glass in its action upon gree 
light, but is inferior to oil of sassafras and oil of cloves. 
89. Zircon: 
This mineral acts less powerfully upon green light than 
crown-glass, but no secondary spectrum was visible when it re- 
fracted in opposition to flint-glass. 
In order to present under a general view the results of the: 
preceding experiments, I have arranged the various substances 
in a Table, inversely according to their action upon green: 
light ; that is, the bodies at the top of the Table form spectra: 
in which the red and green spaces are most contracted, and the: 
blue and violet ones most expanded. The relative position of 
several of the substances, particularly the essential oils, is quite 
empirical ; but it can readily be found by a reference to the 
preceding experiments, whether or not the relative action of 
any two bodies has been actually determined.. To have 
attempted to fix the exact place of every substance, would have 
required a great degree’ of labour, and more time than I could 
easily command; and it is almost certain, that the Table 
would still have been incomplete, as there are many of the 
essential oils, and some minerals, which do not exhibit 
any difference in their action upon green light. Several 
of the oils, too, which I used, had been exhausted by re- 
peated. 
