Experiments and Observations on the Solar Rays. 31 
good mirror. If a piece of white paper on which the colors of 
the spectrum are painted, be held before a highly polished black 
surface and viewed by reflection, the white paper and all the dif- 
ferent colors will be distinctly seen. Having procured a piece of 
anthracite which possessed a smooth, glossy surface, I concentra- 
ted the sun’s rays with a lens alternately upon the smooth surface 
of the coal, and a piece of white china of very fine grain and 
good polish, and threw the reflected rays upon a piece of black 
paper at a small distance from the focus. ‘The rays which were 
reflected from the black surface, appeared to act upon the paper 
as quickly and as forcibly as those reflected from the china; aco- 
pious emission of smoke, accompanied with the odor of burning 
paper, being the result in each case. Pieces of phosphorus also 
were inflamed as quickly, and apparently at as great a distance, 
by the rays reflected from the coal, as by those reflected from the 
china. Indeed, when the two reflecting surfaces were examined 
by the microscope, the polish of the coal appeared to be inferior 
to that of the china. 
Hence it appears that black bodies possess the power of reflec- 
tion in a high degree. Black opacity, then, cannot be owing to 
an inability in the particles of black bodies to reflect the sun’s 
rays. But, since “coal does not transmit to the eye a single ray 
out of those which enter its substance,”* it must be admitted 
that the phenomenon of blackness is produced by the absence of 
free light from the pores of an opaque body. 
As white opacity is the reverse of black opacity, and as white 
bodies appear to detain the greater part of the solar caloric which 
enters their substance, in the same manner that charcoal and oth- 
er black bodies do the intromitted white light, there is strong rea- 
son to believe, that the white light being but feebly attracted by 
the particles of white bodies, a large proportion of it exists with- 
in such bodies in a free state, and then escapes from their pores 
by radiation, as calorie does from heated bodies, and that this ra- 
diation of free white light from the pores of opaque bodies pro- 
duces the phenomenon of whiteness. That the existence of 
free white light within the pores of an opaque body, even coal, 
would produce whiteness, is admitted by Sir Davin Brewster 
himself. In his refutation of that part of the Newtonian theory 
* Brewster’s Life of Newton, chap. vit. 
