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LIV. On the Influence of the Adhesion of Vapour in Experiments 

 on the Absorption of Heat. By G. Magnus*. 



PROFESSOR TYNDALL published in 1861, simultane- 

 ously with myself, an investigation of the transmission 

 of heat through various gases. Both investigations, made inde- 

 pendently of each other and by different methods, yielded the 

 result that gases differ, in their capacity of transmitting heat, so 

 far, that certain of them enclosed in a tube a metre in length 

 transmit less than half the incident heat, while atmospheric air 

 under the same circumstances scarcely interferes with the trans- 

 mission. In this respect the results we obtained agree in gene- 

 ral; but as regards air saturated with aqueous vapour, they ex- 

 hibit the greatest difference. Professor Tyndall found that it 

 absorbs heat to an extraordinary degree, so that, as he expresses 

 itf, comparing a single atom of oxygen or of nitrogen with a single 

 atom of aqueous vapour, the latter absorbs 16,000 times as much 

 heat as one of the former. He afterwards says J that moist air 

 contained in a tube 4 feet in length absorbs 4*2 to 6 per cent, 

 of the total heat which enters the tube. I, on the contrary, had 

 found that no difference can with certainty be established be- 

 tween the absorptive power of air saturated with moisture, and 

 of perfectly dry air at the temperature of the room. 



Prof. Tyndall has since then drawn several conclusions, impor- 

 tant for meteorology, from the great absorptive power of aqueous 

 vapour; and other physicists have followed him in this respect. 

 But it is not merely on account of these conclusions that the 

 question of absorption is important ; for they would still hold, 

 if, instead of transparent aqueous vapour, or aqueous vapour in 

 the proper sense of the word, they referred to aqueous vapour 

 partially deposited, or the nebulous vapour into which transparent 

 vapour changes on the least diminution of temperature. It is 

 in and for itself important to know whether the absorption of 

 heat by moist air is in fact so very much greater than that by 

 dry air. Moreover Prof. Tyndall has doubtless worked with the 

 greatest conscientiousness, which I also am conscious of having 

 done ; and if, in spite of this, there are such extreme differences in 

 our results, the inference is obvious, that circumstances hitherto 

 unknown or disregarded have operated in our experiments. 

 Hitherto we have both of us in vain endeavoured to find any. 

 We were therefore compelled to fortify the results found by new 

 experiments, starting from a different point of view. Thus in 

 the beginning of the year 1866 I published a paper " On the In- 



* Translated from Poggendorff's Annalen for June 1867, No. 2, p. 207. 

 t Phil. Mag. S. 4. vol/xxv. p. 203. % Ibid. vol. xxvi. p. 36. 



