Radiation of Heat by Gaseous Mattei\ 423 



memoir on the Transmission of Heat through Gases*. The 

 published notices of my experiments, commencing in May 1859, 

 had escaped his attention, and his work is therefore to be regarded 

 as independent of mine. Considering the very different methods 

 which we have pursued, the general agreement between us must 

 be regarded as remarkable. 



The starting-point of Professor Magnus's investigation was the 

 interesting experiment of Mr. Grove, in which a platinum wire 

 raised to whiteness by an electric current is suddenly cooled by 

 an atmosphere of hydrogen. This action, which we have hitherto 

 been disposed to attribute to the mobility of hydrogen, and its 

 consequent high convective power, Professor Magnus was led to 

 regard as an effect of conduction ; and the thought induced him 

 to examine the conductivity of gases generally. The mode of 

 experiment adopted led him, not I think to the establishment of 

 gaseous conductivity, but to results substantially the same as 

 those that I had previously obtained. In fact the very experi- 

 ments devised to show conductivity showed in a very striking 

 manner the existence of athermancy, or opacity to radiant heat, 

 in the case of a considerable number of gases. 



The experiments on radiation, where obscure heat was made 

 use of, were thus conducted. Two glass vessels, one much 

 larger than the other, had their bottoms fused together; the 

 larger one being turned upside down, the smaller one stood 

 upright on the top of it. The mouth of the larger vessel was 

 ground down, so that it could be placed like an ordinary receiver 

 on the plate of an air-pump and exhausted, while through proper 

 openings different gases could be afterwards admitted into it. 



To the plate of the air-pump on which the above vessel was 

 placed, was attached a thermo-electric pile with wires leading 

 from it, through the plate, to a galvanometer ; the axis of the 

 pile was vertical, one face of it being turned downwards towards 

 the plate, and the opposite face turned upwards towards the 

 common surface of the two vessels which had been fused together. 



Water was placed in the uppermost vessel, and caused to boil 

 by conducting hot steam through it. Its under surface became 

 thus heated to a temperature of 100° C. But this under surface 

 constituted the upper surface of the vessel underneath. This 

 latter, therefore, possessed a temperature of 100° C. ; and it 

 formed the source of heat made use of in the experiments. 



Here Professor Magnus had a radiating surface of glass — a 

 good radiator — kept at a constant temperature by the hot water 

 above it; at a distance from this surface and turned towards it 

 was the thermo-electric pile, defended from the radiation of the 



* PoggendorfFs Annalen, reprinted in Philosophical Magazine, S. 4, 

 vol. xxii. p. 85. 



