14 REPORT—1840. 
1. Heat from ice. 
2. ———— the hand. 
3. ———— boiling water. 
4. — avesselof mercury underits boiling temperature. 
5. ————— metal smoked ;—wholly non-luminous in the 
dark, heated by an alcohol-lamp behind it. 
6. Heat from incandescent platina (over a spirit-lamp). 
: an oil-lamp (direct). 
8. Otl-lamp heat transmitted by common mica. 
a glass (argand lamp). 
10. ——_—__——_———————-. citric acid. 
Vl. —_—_ —_——— alum. 
12. ———— ice. 
Melloni having shown that a portion of the heat from a lumi- 
nous source is transmitted through certain screens, which are 
wholly opake to light, it became natural to inquire whether the 
rays so passed possessed the properties of heat from dark sources. 
This he found to be partly the case, and partly not. 
The direct test of examining the refrangibility of the heat- 
rays issuing from the screen occurred to Prof. Forbes, who found 
that opake glass and mica act as clear glass and mica do in ele- 
vating the mean refrangihbility of the transmitted heat, an ac- 
tion analogous to that of yellow glass upon light. (See 3rd 
Series, Art. 73, 81, &c.) 
But in all this there was nothing exactly equivalent to the 
action of red glass; this, however, was discovered by Melloni, 
by the happy suggestion of covering the surface of rock salt 
with smoke. 
These remarks introduce more clearly the main object of 
Prof. Forbes in following up the inquiry. In the present paper 
the details of many series of experiments are given, and the 
more precise results now established may be stated as follows : 
I. The peculiar character of the film of smoke on the surface of 
a diathermanous medium, analogous to redness in glass for light, 
was found to be possessed by—1. The simple powder of char- 
coal. 2. Some other dull earthy powders. 3. Surfaces simply 
dull, or devoid of polish. 4. Surfaces irregularly furrowed, as 
with emery or sand-paper. 5. Polished surfaces, on which fine 
distinct lines have been drawn. 6. Transparent mica, when 
mechanically laminated, which, as a continuous medium, pos- 
sesses opposite properties. 
I]. All kinds of heat (i.e. of all refrangibilities) seem affect- 
ed indifferently by the following media :— 
1. The thinnest leaf-gold, which is impervious to any kind of 
heat. 
2. Fine metallic gratings, which transmit all kinds of heat 
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