34 Experiments and Observations on the Solar Rays. 
are separated from each other by interstices filled with a medium 
of less density than the gold itself. As gold is a simple substance, 
the layers must all be equally refracting media. If the strata be 
supposed to be closely joined together, without any interstices 
between them, there certainly can be no reflection at their inter- 
vening planes; for, it was established by Sir Isaac Newron as a 
fundamental principle, that within “the confines of equally re- 
fracting media there is no reflection.” Indeed, that there is un- 
derneath the first surface of gold any other surface which reflects 
light, appears to me in the highest degree doubtful. Unless I 
misapprehend the passage quoted on the preceding page from Sir 
Davin Brewster, his explanation of the mode in which the col- 
ored light is discharged from colored opaque bodies, is based al- 
together on imaginary data, and must therefore fail to give entire 
satisfaction to the true inquirer. 
When the sun’s rays fall upon a piece of anthracite or any 
dense black opaque body, part of the caloric, as has been already 
demonstrated, is reflected from the outer surface, and part of it 
enters the body. A large proportion of that which enters the 
body exists within it in a free state, and then escapes from its pores 
by radiation and otherwise. Except as regards their effects upon 
animal bodies, the one causing the sensation of heat, the other 
that of vision, the rays of caloric and the rays of color bear the 
greatest resemblance to each other. They both come from the 
sun to the earth in the same time; they are both refracted in the 
same manner by lenses, and reflected by specula ; and are equal- 
ly the products of ordinary combustion. Now it appears to me, 
that this analogy gives strong support to the opinion, that a part 
of the light which enters into the substance of colored opaque 
bodies, exists within them in a free state, and then escapes from 
their pores by radiation. 
It will be admitted that the outer and inner particles of any 
simple body possess the same properties. When light falls upon 
an opaque body, “part of it is reflected or driven back, and part 
of it enters the body.” If, as is maintained by Sir Davin Brews- 
rer, and other eminent modern philosophers, the particles of bod- 
ies exercise a specific attraction over the particles of light, the 
outer particles of any colored, opaque, simple body, must attract 
and detain the same sort of rays that the inner particles do. The 
light which is complementary to that which has been detained 
_ by the outer particles of the body, must necessarily be driven off 
