British Association for the Advancement of Science. 297 



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 two distinct sorts of heat, or two 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. 



Abstract of a Paper on the Phcenomena usually referred to the Ra- 

 diation 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- 

 ter was heated 10 or 12 degrees beyond the temperature of the 

 room. The effects were now found to vary according to the di- 

 stance of the canister from the mirror. At a short distance it acted 

 as a cold body, and the varnished side most efficient; on increasing 

 the distance, the effect diminished, and at a certain point altogether 

 ceased ; the thermometer marking zero, whether the Varnished or 

 metallic side was towards it ; but on increasing the distance, the 



Third Series. Vol. 7. No. 40. Oct. 1835. 2 Q 



