368 Prof. Knoblauch on the Influence of Metals 
Yellow glass.| Blue glass. Red glass. } Green glass. 
Polished speculum metal..| 100: 66 100: 35 100 : 50 100: 16 
IBIS ee. ecucrssteeeses= 100 : 66 100 : 35 100: 50 100: 16 
From this it is plain that the heat is in no way changed by 
its reflexion from the mirror of Silbermann’s heliostat. 
In all the observations hitherto recorded, the source of heat 
was the sun’s rays. M. Knoblauch repeated the same experi- 
ments, making use of the lamp of Locatelli with square wick. 
The experiments were made exactly in the manner already de- 
pevibed, and the following Table contains a summary of the 
results :-— 
3 J 
vo » 
5 gd] 5] 8 FE: E 
- = 
H . - o mm a 
Diathermanous 2 ra ile] Se) ap doops, [Sec lense Naas eins 
odies 2 9 = s = 2 a Ral a = 3| £) 3 
; Ss |S|a)/ 2) 8128 S/§|4/538] 8] € 
I alte | a 33 AI 
p 4 o 
Yellow glass..| 100:35) 39 | 35 | 35 | 35 | 35 | 35 | 35 | 35 | 35 | 35 | 34) 35 
Blue glass ...| 100: 29| 30 | 30 | 30 | 30 | 30 | 30 | 30 | 31 | 30 | 30 |31)|30 
Red glass ...| 100: 37| 39 | 37 | 36 | 37 | 37 | 387 | 37 | 38 | 87 | 37 | 39/37 
Green glass...| 100: 14) 14 | 13 | J3 | 14 | 13 | 14 | 14 | 13 | 14 | 14 {13/14 
This Table shows in what different degrees the heat of the sun 
and that of a Locatelli lamp are transmitted through the co- 
loured glasses; and it also shows that when the lamp is used, 
the differences of transmission by the same glass, when heat re- 
flected from different metals is made use of, almost vanish. In 
fact, of all the results obtained with the sun’s rays, the only one 
that continues to assert itself here, is the more copious trans- 
mission of the heat diffusely reflected from gold through the 
yellow glass. 
When, instead of the Locatelli lamp, a metal cylinder heated 
to 110° C. was made use of as the source of heat, the peculi- 
arity observed in the case of gold also disappeared, and the heat 
reflected from it, like that reflected from the other metals, was 
not to be distinguished from the unreflected rays. 
M. Knoblauch next examined the influence of the state of the 
surface on the heat reflected from it. A rough surface of gold 
was compared with a polished surface of the same metal, and the 
heat reflected from both was found to be acted upon in precisely 
the same manner by the coloured glasses. When, however, dif- 
ferent thicknesses of the metal were precipitated by electrolysis 
on a plate of copper, it was found that the heat reflected from 
