REPORT ON RADIANT HEAT. 263 
glasses, &c. The whole experiment was very unsatisfactory. 
Edinb . Journal of Science , N.S. vol. vi. p. 297.) 
c.) Effect of the nature of surfaces on the emission of simple 
heat. 
1. ) Count Rumford {Nicholson's Journal , ix. 60,) employed 
two similar vessels of hot water of the same temperature; one 
naked, the other coated with linen, glue, black or white paint, 
or smoked with a candle : the results were, 
Naked vessel cooled 10° in 55 m 
Coated-- 10 — 36\ 
Mr. Murray supposes a relation between radiating and con¬ 
ducting powers. (,System of Chem. i. 326, 33 4. See Phil. 
Trans . 1804, p. 90, &c.) 
2. ) The most complete investigation of this and other parts 
of the subject has been made by Professor Leslie in his Inquiry 
into the Nature and Propagation of Heat, 1804. 
He first used hot water in a globe of tin, in which the in¬ 
serted thermometer fell a given quantity, with the tin bright, 
in 156 ra ; with the tin coated with lamp-black, in 81 m . 
The difference was greatest in still air, and diminished with 
the violence of its motion: 
Time of Cooling. 
Wind. Bright. Blackened. 
Gentle . 44 m . 35 m 
Strong . 23 . 20\ 
Violent . 9| . 9 
Hence the effect is different from conduction by air. 
3.) The most exact series of experiments was that in which 
he used conjugate reflectors, a differential thermometer having 
one bulb in the focus, and a cubical tin canister of hot water 
(the temperature of which was seen by the projecting stem of 
a thermometer,) and each side of which could be coated with a 
different substance, and presented successively towards the re¬ 
flector. 
The following results collected together afford the best view 
of the general nature of the conclusions relative to the influence 
of the state of the surface on the radiation of heat. ( Inquiry , 
pp. 81, 90, 110.) 
Lamp-black . 100* 
Water (estimated) .. 100 
Writing-paper . 98* 
