TRANSACTIONS OF THE SECTIONS. 
9 
On certain 'points connected with the recent Discoveries relative to 
Radiant Heat. By Professor Powell. 
In this communication the author expressed his particular satis¬ 
faction in finding that M. Melloni (in his second memoir) describes 
a repetition of the experiment originally made by him, and recorded 
in the Philosophical Transactions, 1825, with perfect success, by 
means of his extremely delicate apparatus. The confirmation is 
the more complete, as the experiment was made by M. Melloni with 
a different view. 
It is thus now established beyond question, that luminous hot 
bodies are sending out tw r o distinct sorts of heat, or tw T o distinct 
heating agents, at the same time, differing in their properties and 
mode of operation. 
Hence the whole series of results of M. Melloni must be inter¬ 
preted with reference to this distinction, and possibly the considera¬ 
tion of it may remove some of the apparent anomalies. 
Another question of importance which has occurred to the author 
is this,—Whether, in the polarization apparatus, supposing one glass 
or pile of mica heated, it will radiate the same quantity of heat to 
the other in the two rectangular positions. The question is purely 
a mathematical one, and has been in some degree considered, at the 
author’s suggestion, by Mr. Murphy, of Cambridge. The integra¬ 
tion has not been completed, but Mr. Murphy thinks it clear that 
there will be a difference. 
On the Phenomena usually referred to the Radiation of Heat. By 
Henry Hudson, M.D ., M.R.I.A ., Dublin. 
For the purpose of repeating Leslie’s experiments with variations 
of the temperatures of the surface of the.mirror and of the thermo¬ 
meter, the author procured a parabolic zinc mirror with a hollow 
back, so that its surface could be heated or cooled by filling it with 
hot or cold liquids. 
The following are the results obtained : 1st, Whatever be the tem¬ 
perature of the room, if the mirror and canister be at the same tem¬ 
perature also, there is no effect produced by either the metallic or 
the varnished side of the canister. 2nd, If the canister (alone) be 
above the temperature of the air, the varnished side produces a 
greater heating effect than the metallic side, in the proportion of 
about 12 : 1. 3rd, If the canister (alone) be below the temperature 
of the room, the varnished side produces a greater cooling effect 
than the metallic in the same proportion of about 12 : 1. 4th, If the 
mirror be heated considerably (say to 200° Fahr.), and the thermo¬ 
meter so arranged that both balls are equally warmed by the mir¬ 
ror (one of them being in the focus), a canister (at the same tem¬ 
perature as the room) produces a cooling effect on the focal ball, 
and the varnished side displays its superior efficiency. 5th, The 
mirror and thermometer being as in the last experiment, the canis- 
