Radiation of Heat by Gases and Vapours. 183 



For these tensions the absorption of radiant heat by the 

 vapour of sulphuric ether is more than twice the absorption of 

 olefiant gas. We also observe that in the case of the former 

 the successive absorptions approximate more quickly to a ratio 

 of equality. In fact the absorption produced by 4 inches of 

 the vapour was sensibly the same as that produced by 5. 



But reflections similar to those which we have already applied 

 to olefiant gas are also applicable to ether. Supposing we make 

 our unit-measure small enough, the number of rays first destroyed 

 will vanish in comparison with the total number, and for a time 

 the fact will probably manifest itself that the absorption is 

 directly proportional to the density. To examine whether this 

 is the case, the other portion of the apparatus, omitted in the 

 general description, was made use of. K is a small flask with a 

 brass cap, which is closely screwed on to the stopcock c\ Be- 

 tween the cocks c' and c, which latter is connected with the ex- 

 perimental tube, is the chamber M, the capacity of which was 

 accurately determined. The flask k was partially filled with 

 ether, and the air above the liquid removed. The stopcock c 1 

 being shut off and c turned on, the tube S S' and the chamber 

 M are exhausted. The cock c is now shut off, and c' being 

 turned on, the chamber M becomes filled with pure ether vapour. 

 By turning d off and c on, this quantity of # vapour is allowed to 

 diffuse itself through the experimental tube, and its absorption 

 determined; successive measures are thus sent into the tube, 

 and the effect produced by each is noted. Measures of various 

 capacities were made use of, according to the requirements of the 

 vapours examined. 



In the first series of experiments made with this apparatus, I 

 omitted to remove the air from the space above the liquid; each 

 measure therefore sent in to the tube was a mixture of vapour 

 and air. This diminished the effect of the former; but the 

 proportionality, for small quantities, of density to absorption 

 exhibits itself so decidedly as to induce me to give the observa- 

 tions. The first column, as usual, contains the measures of 

 vapour, the second the observed absorption, and the third the cal- 

 culated absorption. The galvanometric deflections are omitted, 

 their equivalents being contained in the second column. In 

 fact as far as- the eighth observation, the absorptions are merely 

 the record of the deflections. 



