RADIANT HEAT, AND ITS CONVERSION THEREBY INTO SOUND. 
297 
over a heated surface of polished silver, the radiation from that surface was augmented 
as it might have been by a coating of isinglass or lampblack. 
A surmise has been mentioned regarding new allotropic conditions, as occurring to 
me amid the perplexities of my earlier experiments. In one instance—that of electro¬ 
lytic oxygen—the surmise proved correct. My first experiments indicated that the 
modicum of ozone which went forward with the oxygen, exerted four times the 
absorption of the gas in which it was diffused.* Subsequently, by changing the appa¬ 
ratus, and taking pains to augment the quantity of ozone, the multiple rose succes¬ 
sively from 4 to 20, 35, 47, 85, ascending finally to 136.t The behaviour of ozone 
was thus proved to be similar to that of molecules composed of heterogeneous atoms. 
Hence the conclusion, drawn at the time, that the molecule of ozone was formed of 
oxygen atoms so grouped as to render their action upon radiant heat virtually that 
of a compound body. This, it is needless to say, is the constitution now assigned 
to ozone. 
With the view of including corrosive gases and vapours among the number of those 
examined, and for other reasons, the brass experimental tube was displaced by a tube 
of glass of the same diameter and nearly 3 feet long. The source of heat was also 
changed from a Leslie’s cube, containing boiling water, to a plate of copper against 
which a sheet of flame was permitted to play. Extraordinary precautions were found 
necessary to insure perfect steadiness on the part of the flame. With this arrange¬ 
ment the practical inability of the elementary gases to absorb radiant heat was further 
illustrated and confirmed. Chlorine gas and bromine vapour, for example, were 
proved to be highly diathermanous. 
At the pressure of an atmosphere it was found that the diathermic range of 
colourless gases extended from 1 to about 1000. The portion of gas first entering 
the experimental tube, having the whole heat to act upon, produced, as might be 
expected, the greatest effect, the increment of absorption, after a certain quantity ol 
gas or vapour had entered, being infinitesimal.^ It was therefore interesting to 
* Philosophical Transactions, Vol. 151, p. 8. 
f Ibid., Vol. 152, pp. 84, 85. 
t This is well illustrated by an experiment on sulphuric ether vapour recorded in the Bakerian Lecture 
for 1861:— 
Pressure. Absorption. 
1 inch 214 
2 „ 282 
3 „ 315 
4 „ 330 
5 „ 330 
The absorption of air being taken as unity, that of sulphuric ether vapour at 1 inch mercury pressure 
is here shown to be 214. When, however, vapour corresponding to a pressure of 4 inches was already in 
the experimental tube, the addition of another inch did not sensibly augment the absorption. 
MDCCCLXXXII. 0 
2 Q 
