364 Prof. Knoblauch on the Influence of Metals 
interposed, 59 parts out of the 100 passed through it. When 
the heat, instead of being reflected by the glass (G), was sent 
through it, 80 parts out of 100 passed through the interposed 
yellow glass. The other glasses were afterwards tried: the 
results are stated in the following Table :— 
Yellow Blue Red Green 
glass. glass. glass. glass. 
Heat reflected from glass (G) ...... 100:59} 100:44) 100: 44] 100: 20 
[eat transmitted through glass (G).| 100: 80} 100:51] 100: 64] 100: 19 
Here also the deportment of the reflected heat towards the 
coloured glasses is very different from that of the transmitted heat. 
The antithesis existing between the gold and the blue-yellow 
glass will also be remarked. While, in the case of gold, the 
reflected rays are more capable of passing through the yellow, 
blue, and red glass, and less capable of passing through the green 
glass than the transmitted rays; in the case of Goéthe’s glass 
the reflected heat was less capable of passing through the yellow, 
blue, and red glass, and more capable of passing through the 
green than the transmitted heat. 
il. 
Twelve years ago M. Knoblauch had treated the question, 
whether, by its reflexion from rough metallic surfaces, radiant 
heat was so changed as to be distinguishable from unreflected heat. 
Melloni entertained the opinion that metallic surfaces behaved 
towards radiant heat as white bodies towards light. M. Knob- 
lauch believed that he had confirmed this view; but since then 
MM. Provostaye and Desains have made experiments with 
metals, from which the authors conclude that different kinds of 
heat are unequally reflected from metallic surfaces. As to the 
properties of heat diffusely reflected from different metals, no- 
thing further is known ; but now that in the case of three metals 
differences in the heat transmitted by them have been detected, 
the examination whether changes occurred in the reflected heat 
could be undertaken with greater hope of success. 
The beam reflected from the heliostat was first permitted to 
fall direct upon the thermo-electric pile, and the consequent 
effect was denoted by 100. The yellow, blue, red, and green 
glasses were then interposed successively in the path of the rays : 
the relative quantities of heat which passed through the glasses 
are given in the following Table :— 
Green glass. 
100: 18 
Red glass. 
100: 51 
Yellow glass. 
100 : 66 
Blue glass. 
100 : 36 
