upon Radiant Heat. 363 
tative differences which subsequently showed themselves would 
not have appeared. 
It is also known, that if to the heat passing through the aper- 
tures in the silver, that of the silver itself had been added, the 
resulting heat would be different in quality from that falling 
upon the silver. But the heat in the above experiments showed 
no such difference of quality, and hence no sensible portion of it 
can have been derived from the silver. 
But supposing the thin metallic layer to be warmed and con- 
verted into a source of heat; the heat thus radiating from a 
less intense source must have passed through the coloured glasses 
in less quantity than the solar rays alone. Now the experiments 
show the reverse of this to be the case; for while of the direct rays 
only 20 in 100 pass through the yellow glass, of the rays which 
have passed through the layer of gold 54 out of 100 are trans- 
mitted. 
M. Knoblauch next examined the heat which was reflected 
from the anterior surface of the layer of gold; an experiment 
was also suggested by the fact of his possessing a piece of 
glass (G) which had served to illustrate Goéthe’s theory of 
colours. This glass transmitted yellow light, and reflected a 
bluish light. It was therefore antithetical to the gold, which 
transmitted a bluish light, but reflected yellow. 
The solar-rays were permitted to pass through the glass lens 
and to enter the dark room, where they were reflected from the 
dull surface of gold, and afterwards permitted to fall upon the 
thermo-electric pile. We will call the quantity of heat thus mea- 
sured by the deflection of the galvanometer 100. A yellow glass 
was now placed in the path of the rays, and a quantity of heat 
expressed by the number 70 passed through the glass. When, 
however, the heat passed through the gold, only 14 parts out of 
100 were capable of passing through the yellow glass. The 
other glasses were used in the same manner, with the following 
results :— 
Yellow glass.| Blue glass. | Red glass. | Green glass. 
Heat reflected from gold ...... 100: 70 100: 45 100:56 | 100:19 
Heat transmitted through gold.| 100: 19 100: 31 100:14 | 100:26 
The experiments illustrate the extraordinary difference exist- 
arate ie the heat reflected by gold and the heat transmitted 
y it. 
In the next place, the rays were suffered to fall upon the glass 
already mentioned. Calling the quantity reflected from the 
glass (G) and falling on the pile, 100; when the yellow glass was 
