upon Radiant Heat. 365 
The question now is, whether the calorific rays which have 
been diffusely reflected from metallic surfaces possess the same 
power of penetrating the coloured glasses as those which have 
not been thus reflected. 
A rough surface of gold was first made use of. Express- 
ing the action of the heat reflected from this surface, and falling 
direct upon the pile by 100, the proportional quantities which 
pees through the coloured glasses are given in the following 
able :— 
Yellow glass. Blue glass. Red glass. Green glass. 
100:73 | 100:37 100 : 55 100 : 17 
It is here unmistakeable that a more copious passage takes 
place through the yellow glass than in the case where the heat 
was unreflected. The ratio in the latter case is only 66 : 100, 
while in the case now before us it is 73: 100. Through the red 
glass also the transmission has been more copious, the ratio in- 
creasing from 51 : 100 to 55 : 100. 
When the gold plate was exchanged for a rough plate of silver, 
or for a dull surface of platinum, the following ratios were ob- 
tained :— 
Yellow glass. Blue glass. Red glass. Green glass. 
Silver .2.<:<ee- | 100 : 72 100 : 38 100 : 55 100 : 17 
Platinum......| 100: 66 100 : 38 100: 51 100; 18 
Here we observe that the heat reflected from silver shows 
the same deportment as that reflected from gold. The rays 
in both cases are more capable of passing through the yellow and 
red glasses than the unreflected rays. The heat reflected from 
the platinum surface, on the contrary, is not to be distinguished 
in its action from the direct rays. The small difference which 
shows itself in the case of the blue glass, lies within the limits of 
the errors of observation. 
Hence the same metals (that is, gold and silver) that alter 
the properties of the calorific rays which pass through them, 
exert also an influence upon the rays diffusely reflected from 
their surfaces, while platinum in both cases leaves the rays un- 
changed. # 
Other metals were next examined; the results are given in 
the following Table :— 
