Prof. Magnus on the Propagation of Heat in Gases. I 1 



It follows from these numbers that hydrogen really conducts 

 heat in a manner similar to the metals ; for the temperature 

 which a thermometer placed in it ultimately assumes is higher 

 as the gas is denser. 



Of all gases this is only the case with hydrogen, with all the 

 others the temperature is higher when they are more rarefied. 

 It follows therefore that these gases oppose a hindrance to the 

 transmission of radiant heat, and that they are athermanons to 

 such an extent that their athermancy exercises a greater resist- 

 ance than their capacity to conduct heat. This property is, 

 however, not entirely absent ; for, apart from other reasons already 

 adduced by Dalton and Biot, which speak for a conductibility of 

 heat by gases, it would be contrary to all other known laws if 

 we assumed that the capacity of conducting heat was confined to 

 hydrogen. But it is certainly very remarkable that this gas, the 

 lightest of all, possesses the greatest conductibility. 



This surprising result has led me to undertake a few experi- 

 ments with a view of removing, as far as possible, any doubt as to 

 conductibility. For as the upper part of the side of the vessel 

 A B in the neighbourhood of C also became gradually heated, 

 it might be supposed that although the temperature of this side 

 decreases from above downwards, yet that currents are produced 

 in the gases contained in A B, and that the differences of tempe- 

 rature observed only arise from these currents. This assumption 

 is indeed refuted by the fact that, owing to currents, the tempera- 

 tures in an exhausted space cannot be higher than in one filled 

 with air. In order to remove every objection, I repeated the ex- 

 periments just mentioned in such a manner that the apparatus 

 AB, or an entirely similar one, was filled with a light substance, 

 with feathers or eider-down, or with cotton wool. It then ap- 

 peared that the denser the light substance, the higher was the 

 temperature which the thermometer assumed. This higher tem- 

 perature was therefore certainly not produced by a motion of the 

 air. When the air among the cotton was removed as completely 

 as possible, the thermometer did not attain the same temperature 

 as before, when the interstices were filled with air. The small 

 difference might be caused by an alteration in the density which 

 the cotton had experienced on exhausting the air in the neigh- 

 bourhood of the thermometer ; for the various observations made 

 with the same quantity of cotton gave similar deviations. But 

 when hydrogen was introduced among the cotton, the thermo- 

 meter always rose higher than when the space was filled with 

 atmospheric air. Hydrogen produced the same effect, whether 

 eider-down or cotton wool was used. The following are a few of 

 the numbers : — 



