on the Production of Light and Heat. 281 
may condense its parts, and diminish its capacity for heat or 
light. There is, however, a strong analogical argument for 
the transparency of the gold : every body whatever, when 
extremely thin, is pervious to light in such quantity as to be 
perceptible to our eye-sight : thus gold, perhaps the most 
opake of all bodies, platina excepted, when beaten into leaf 
gold, is so pervious to the green rays, that, if held close to the 
eye, all objects are seen through it with considerable distinct- 
ness, appearing of a deepish green hue. Now the particles of 
matter in the gold plate being much separated from one ano- 
ther, if not more regularly arranged, by the heat; and the in- 
tensity of the light in the explosion of the grains of gun- 
powder being so great ; it is not improbable that some few 
rays may be transmitted through the gold. 
After some reflection upon the curious result of experiment r, 
I am inclined to think, that the blackened cylinder does not 
begin to shine at so low a temperature as the polished one ; 
and, consequently, that the commencement of ignition is not, in 
all cases, a certain indication of a particular temperature. For, 
when the two cylinders were removed from the ignited cru- 
cible (see Fig. 1.) the blackened one looked of a brighter red 
than the polished, and yet, in the course of cooling, disappeared 
in about two-thirds of the time that the polished one conti-. 
nued to shine, without any apparent reason for its cooling at 
a faster rate. Should it not, therefore, seem that it requires a 
greater heat to make it shine ? 
I am well aware, that these appearances may be differently 
explained ; and, to determine this point, I would propose the 
following experiment. Put larger cylinders into the tube ; and, 
having made them red hot, drop them separately, each at the 
