upon Radiant Heat. 367 
contained in the following Table, to construct which it was 
necessary to connect by new experiments the results exhibited 
separately in the foregoing Tables, and to reduce them after- 
wards to a common standard. 
2 | 
By : 2 3 8 
a 8 s 5 3 = 
3 ia etc i Sau is =) aS Kcr a. A 
Diathermanous 2 ne 5 I 5 3 g g a|3)/Sd] 2] 2 
2 ° > S =) = t <j a olus s s 
bo 2 =| 3 = a = N ° So] el a 
ys C=] o 5 = 5 a =| aq 
31 a “4 1S) b a 
I =| rs) oS 5 
E| = =| 2 
P =] 4 o 
Yellow glass..| 100: 65) 73 | 72 | 65 | 72 |. 66 | 65 | 65 71 | 65} 65 | 70/ 65 
Blue glass ...| 100: 40) 39 | 40 | 40 | 40 | 40 | 40 | 40 | 40 | 40/ 40 | 39/ 40 
Red glass ...|100:51) 55 | 55 | 51 | 55 | 52 | 51 | 51 | 54 | 51) 51 | 52/51 
Green glass...) 100:17| 16 | 16 | 17 | 17 | 17 | 17 | 17 | 16 | 17) 17 | 17/17 
The results recorded in this Table are regarded by M. Knob- 
lauch as placing beyond doubt the following proposition :— 
that certain metals, as gold, silver, mercury, copper, brass, alter the 
calorific rays (as coloured bodies alter those of light); while 
other metals, as platinum, iron, tin, zine, lead, an alloy of lead and 
tin (similar to colourless transparent bodies as regards light), 
do not change the calorific rays by reflexion. 
M. Knoblauch also shows, in a very convincing manner, that 
the results obtained could not be due to the heat emitted by the 
metals themselves after they had been warmed by the sun’s rays. 
We have seen that reflexion from certain metals can alter the 
quality of the heat; but the heat made use of in the experi- 
ments had been actually reflected from the mirror of the helio- 
stat. It was necessary therefore to examine whether the variety 
of the sun’s rays was not altered by this first reflexion. The 
heliostat made use of was that of Silbermann, and its mirror 
was of highly polished speculum metal. 
M. Knoblauch first examined the influence of a steel mirror 
upon the calorific rays, and found it absolutely nothing; which, 
indeed, was to be inferred from the deportment of the rough 
iron surface already recorded. He then set a heliostat of 
August, which possessed a steel mirror, in the place of that of 
Silbermann, and compared the heat reflected from the mirror 
of the latter with that reflected from platmum. He knew from 
the observations already recorded, that platinum produced no 
change whatever in the calorific rays reflected from it. For the 
sake of making the conditions of the two experiments as much 
alike as possible, the heat reflected from platinum was preferred 
to the direct heat. The following Table gives the ratios of the 
heat incident upon, to that transmitted by the coloured glasses 
in the case of both metals :— 
