EADIATION OF HEAT BY OASEOUS MATTEE. 
77 
The paradox ah’eady referred to is here solved, and the explanation given of the extra- 
ordinary effect observed in the case of the alcohol and ether vapours when dry air 
entered the experimental tube. Dynamic radiation, moreover, and dynamic absorption 
go hand in hand ; and if we compare both with Table III., we shall find the order of the 
substances precisely the same, although one set of results are obtained with a source of 
heat external to the gaseous body, and the other with a source of heat and cold within 
the body itself. Had I snfiicient time at my disposal, I could develope this subject with 
advantage. The results just recorded constitute my first regular series of experiments, 
and no doubt augmented experience will enable me to attain more perfect results. 
I could not well obtain half an inch of my most energetically acting vapour, namely, 
boracic ether ; but one-tenth of an inch admitted into the tube and dynamically heated 
and chilled, gave — 
Eadiation. Absorption. 
66° 28° 
Seeing the astonishing energy with which some of these vapours absorb and radiate 
heat, it may be asked how far the quantity of vapour may be reduced before its action 
becomes insensible. At present I will not venture to answer this question fully ; 
certainly we should be dealing at least with millionths of our smallest weights. But I 
will here lay before the Society an account of one experiment, the result of which can 
hardly fail to excite astonishment. The experimental tube being exhausted, one-tenth 
of an inch of boracic ether vapour was admitted into it ; the barometer stood at 30 inches 
at the time, hence the tension of the vapour within the tube was of an atmo- 
sphere. 
Dynamically heated by dry air, the radiation of this vapour’ produced a deflection 
of 66°. 
The tube was then exhausted to 0’2 of an inch, and the quantity of vapour reduced 
thereby to y^th part of its first amount ; the needle was allowed to come to zero, and 
the residue of vapour was djTiamically heated as before : its radiation produced a deflec- 
tion of 42°. 
The pump was again worked till a vacuum of 0’2 of an inch was obtained, this residue 
containing of course y^th of the quantity of ether present in the last. On dynamically 
heating this residue, its radiation produced a deflection of 20°*. 
Two additional exhaustions, succeeded by dynamic heating, gave the deflections 14° 
and 10° respectively. 
Tabulating the results so as to place each deflection beside the vapour-tension which 
produces it, we have the following -view of the experiment : — 
♦ This is less than the truth ; my assistant having executed three or four strokes of the pump inadvert- 
ently while the dry air was not shut off, removing thereby a considerable proportion of the vapour which 
ought to be present at this stage of the experiment. 
