30 Experiments and Observations on the Solar Rays. 
ternal parts of the body would be instantaneous, contrary to what 
is observed to occur. 
Since coal and all black opaque bodies appear to have the pow- 
er of separating the intromitted white light from the caloric, of 
detaining the former and rendering it latent, and allowing the 
latter to exist within the pores in a free state, and since white 
opacity is the reverse of black opacity, it seems rational to infer 
that the action of white bodies upon light is the reverse of that 
of black bodies, that their particles attract and detain the caloric, 
but, having little affinity for the white light, a large proportion of 
the latter exists within the pores in a free state, and then escapes 
by radiation. 
“Those bodies which possess the power of reflection in the 
highest degree, such as white metals, chalk and plaster of Paris, 
never reflect more than one half of the light which falls upon 
them; and coal reflects from its first surface only one twenty 
fifth of the white light.”* Now, supposing that black paper pos- 
sesses the same absorptive power as charcoal, and that the rays 
which pass into the substance of white paper are disposed of in 
the same manner as those which pass into the substance of black 
paper, it follows, that a condensation of rays equal to 122 upon 
white paper, should produce the same heating effect as a conden- 
sation of rays equal to 1 upon black paper. But it has already 
been shown, that, when the rays are condensed sixteen times as 
forcibly on white as on black paper, less tendency to combustion 
is produced in the former than in the latter. How can the dis- 
appearance of so much caloric be accounted for, unless it be sup- 
posed that the particles of the white paper attract and detain it, 
in the same manner that those of coal and other black bodies do 
the intromitted white light ? 
The opacity of blackness was ascribed by Sir Isaac Newron 
to an inability in black bodies to reflect light, owing to the ex- 
treme smallness of their particles. But it is now well known 
that black bodies reflect a considerable quantity of light. Coal 
reflects one twenty fifth of the rays which fall upon it, and other 
black bodies of greater density appear to reflect a larger quantity 
than this. Black marble or any dense black body, when highly 
polished, possesses sufficient reflecting power to form a tolerably 
* Brewster's Life of Newton, chap. vit. 
