Experiments and Observations on the Solar Rays. 33 
thickness of the body, or, what is the same thing, the color re- 
flected to the eye, is complementary to that which has been de- 
tained by the particles of the body, while the light is passing and 
repassing through a thickness terminated by the reflecting surfa- 
ces,” g&c.* 
The arguments advanced by this philosopher, in support of the 
opinion that the particles of bodies exercise a specific attraction 
over the particles of light, are forcible and convincing ; but that 
part of his theory, which has for its object the determination of 
the manner in which the colored light is discharged from colored 
opaque bodies, will not, it appears to me, bear a thorough exami- 
nation. When he says that “the color reflected to the eye is 
complementary to that which has ‘been detained by the particles 
of the body, while the light is passing and repassing through a 
thickness terminated by the reflecting surfaces,” he means, I pre- 
sume, that the colored light is reflected to the eye from the se- 
cond iorfand of a thin transparent stratum, the complementary 
light having been detained by the particles composing this stra- 
tum. According to this theory, the thinnest strata of all colored 
Opaque bodies are transparent. But this is by no means certain. 
There is reason to believe that the thinnest film which can be 
formed of any metal is opaque. Gold leaf, it is true, transmits a 
portion of colored light, but, when it is examined by the solar 
microscope, it is said that innumerable rents can be perceived 
within it; wherefore, it is probablesthat the light which is trans- 
mitted pastes through openings which have been caused by a for- 
cible separation of the particles. The gold which covers the sil- 
ver of which gold wire is formed, is vastly thinner than gold leaf. 
According to the computation of Dr. Haury, the ten thousandth 
part of a grain of gold covers a piece of wire one eighth of an 
inch in length, “and yet, though the gold with which such 
wire is coated is stretched to such a degree, so intimately do its 
parts cohere, that there is not any appearance of the silver under- 
neath.”+ Even supposing a colored opaque body, a piece of gold 
for instance, to be composed of thin transparent strata, still, it is 
difficult to conceive how there can be any reflection except from 
the first surface of the gold, unless it be supposed that the layers 
* Life of Newton, chap. v11 
t Greg. Dict. of Arts and cl. Articles Ductility and Wire. 
Sxconp Srnizs, Vol. I, No. 1.—Jan. 1846. 5 
