4o8 Dr. Brewster on new Properties of light exhibited 
light never appears, and is therefore caused by some internal 
structure which cannot be communicated to other bodies. 
When an impression is taken from the fracture of mother of 
pearl, its faculty of producing colour is also communicated. 
In imparting to gum Arabic and balsam of Tolu, the super- 
ficial configuration of mother of pearl, we are enabled, on 
account of their transparency, to observe the changes induced 
upon the transmitted light. The extraordinary images formed 
by reflection were both visible, the primary one being re- 
markably brilliant, and the secondary one scarcely perceptible ; 
but when the light was transmitted through the gum the 
primary image was nearly extinct, while the secondary one 
was unusually brilliant and highly coloured, far surpassing in 
splendour those which are formed by transmission through 
the mother of pearl itself. When both the surfaces of gum 
Arabic are impreissed with mother of pearl, four images are 
seen. The colours seen by transmission are more brilliant in 
the gum than in the balsam, as the latter has the greatest 
reflective power ; but the coloured images produced by re- 
flection do not seem to have suflered a greater dispersion, 
when they are formed by the metals, than when they are 
formed by cements. 
When the impression is taken from a pearl, the wax re- 
ceives a character similar to that which is possessed by the 
pearl. The image reflected from the surface of the pearl is 
enveloped in a quantity of unformed light, arising from a cause 
which v.'ill afterwards be explained; and the very same white 
nebulosity is reflected from the wax. 
