Radiation of Heat by Gases and Vapours. 



185 







Table V.— Sulphuric Ether. 







Unit-measure T £ n tn of a cu 



bic inch. 







Absorption . 



Measures. 



Absorption. 



Measures. 



Observed 



> 

 Calculated. 



i 

 Observed. 



Calculated. 



1 



5-0 



4-6 



17 



655 



77-2 



2 



10-3 



9-2 



18 



68-0 



83-0 



4 



19-2 



18-4 



19 



70-0 • 



87-4 



5 



24-5 



23-0 



20 



720 



92-0 



6 



29-5 



27-0 



21 



73-0 



967 



7 



34-5 



32-2 



22 



73-0 



101-2 



8 



38-0 



36-8 



23 



73-0 



1053 



9 



440 



41-4 



24 



77-0 



110-4 



10 



46-2 



46-2 



25 



78-0 



1150 



11 



50-0 



50-6 



26 



78-0 



1196 



12 



52-8 



55-2 



27 



800 



124-2 



13 



55-0 



59-8 



28 



80-5 



128-8 



14 



57-2 



64-4 



29 



81-0 



133-4 



15 



59-4 



69-0 



30 



810 



1380 



16 



62-5 



73-6 









We here find that the proportion between density and absorp- 

 tion holds sensibly good for the first eleven measures, after which 

 the deviation gradually augments. 



I have examined some specimens of ether which acted still 

 more energetically on the thermal rays than those above recorded. 

 No doubt for smaller measures than y^th of a cubic inch the 

 above law holds still more rigidly true ; and in a suitable loca- 

 lity it would be easy to determine with perfect accuracy ^th of 

 the absorption produced by the first measure ; this would corre- 

 spond to - * th of a cubic inch of vapour. But on entering 

 the tube the vapour had only the tension due to the temperature 

 of the laboratory, namely 12 inches. This would require to be 

 multiplied by 2*5 to bring it up to that of the atmosphere. 

 Hence the -L t h of a cubic inch, the absorption of which I have 

 affirmed to be capable of measurement, would, on being diffused 

 through a tube possessing a capacity of 220 cubic inches, 

 have a tension of ^ x i x jJ^—^th part of an atmo- 

 sphere ! 



I have now to record the results obtained with thirteen other 

 vapours. The method of experiment was in all cases the same 

 as that just employed in the case of ether, the only variable ele- 

 ment being the size of the unit-measure ; for with many sub- 

 stances no sensible effect could be obtained with a unit volume 

 so small as that used in the experiments last recorded. With 

 bisulphide of carbon, for example, it was necessary to augment 

 the unit-measure 50 times to render the measurements satisfac- 

 tory. 



PhiL Mag. S. 4. Vol. 22. No. 146. Sept. 1861. O 



