278 
SECOND REPORT - 1832 . 
Rise of Thermometer in 1 min. centig. 
Source of Heat. 
. fVessel of mercury, 
’ \ temp. 180° cent. 
Q j Vessel of mercury, 
boiling, 346° . . 
3. Iron, 427 c 
4. Copper, 960° (1.) 
5. Ditto (2.) 
g J Argand lamp—no 
’ p chimney . . 
^ f Argand lamp- 
' \ chimney . . 
c ~—-- 
No Screen. 
3°*94 . . 
16 -33 . . 
32 *8 
38 *97 . . 
71 *54 . . 
21 -12 . . 
23 *44 . . 
Transparent Blackened 
Screen. Screen. 
. 0°-22 .... 0°-07 
. 1 *36 .... 0 -17 
. 4 -70 .... 0 -31 
. 11 -83 .... 0 *40 
. 21 -41 .... 0 *73 
. 7 *29 .... 0 -21 
. 12 -82 .... 0 *23 
The two first experiments of this series have been already 
considered. The 3rd, or iron at 427° centig., was at a red 
heat, its temperature of luminosity in the dark being about 
400°. This, therefore, and the subsequent part of the series 
are affected by the consideration that light was emitted, which 
materially alters the case, as we shall presently observe. 
De la Roche infers from these experiments, that a portion of 
simple radiant heat is transmitted directly in the w 7 ay of radia¬ 
tion through glass; and that this increases as the temperature 
is raised. 
A thick glass, though very transparent, stops heat more than 
a thin glass less so; the difference is less as the temperature 
is raised. 
A portion of the heat having been intercepted by one screen, 
a proportionally much less diminution is caused by the introduc¬ 
tion of a second; hence he infers that the rays emitted of a hot 
body are of several kinds, possessing different degrees of power 
to pass through glass. 
He views the results, when the source of heat is raised to the 
temperature of luminosity, as forming one connected series w r ith 
those below that point, and thus conceives a gradual advance 
in the radiant matter or agent, from the state of simple heat 
towards that of light or “ luminous heat.” 
6.) The theory adopted by De la Roche, as well as by Biot 
(Traite de Phys. iv. 640,) and Leslie, is that of one simple 
agent, which, as the temperature of the source is raised, is 
gradually brought more into the state of light, which on ab¬ 
sorption is reconverted into heat. At low temperatures it is 
wholly or nearly all stopped by transparent screens. At in- 
