Experiments and Observations on the Solar Rays. 37 
one half of the light which falls upon it. Let a quantity of 
white light equal to two, fall upon a piece of chalk, and another 
quantity of white light equal to twenty five, fall in the same di- 
_ rection on a piece of charcoal of the same size and shape as the 
chalk, and which has the same position. Under these circum- 
stances the charcoal must reflect as much white light as the chalk. 
But the coal will still appear black, while the chalk will preserve 
its whiteness. 
The explanation of white and black opacity given by optical 
writers, must be erroneous; for, the whiteness of chalk is per- 
ceptible in a dark, cloudy night, whereas charcoal appears intense- 
ly black, even though viewed by the direct light of the sun, 
when the sky is cloudless and the ground covered with snow. 
It is asserted by Sir Davin Brewsrer, that “coal does not 
transmit to the eye a single ray out of those which enter its sub- 
stance.” Now, if when an opaque body discharges no light 
whatever from its internal s, we have the phenomenon of 
blackness, even though the quantity of light reflected from its 
external surface is considerable, it must I think be admitted, that 
when such a body possesses a proper color, its color is owing to 
the radiation of colored light from its pores. 
In making a brief recapitulation of the views unfolded in this 
paper, I would say that the particles of all opaque bodies exercise 
over the intromitted rays a specific attractive power. Those of 
coal and other black bodies attract and detain the white light, but, 
having a feeble affinity for the caloric, the latter exists within 
such bodies in a free state, and then escapes from their pores by 
radiation and otherwise ; the particles of white bodies detain the 
calorie, but, having less affinity for the white light, a large pro- 
portion of the latter exists within these bodies in a free state, and 
then escapes from their pores by radiation ; and the particles of a 
body whose color is one of the primary colors of the spectrum, 
attract and detain the light which is complementary to that which 
gives the body its proper color, the latter, being left free, escapes 
from the internal parts of the body, by that self-repellent power of 
its particles which is known to exist, and is the cause of radiation. 
. This theory is one of extreme simplicity ; but it is not for t 
reason the less likely to be true. We are taught by Sir Isaac 
Newron, that “ Nature does nothing in vain, but is simple, and 
delights not in superfluous causes of things.” 
