OF HIGH liEFEANGIBlLITY UPON GASEOUS MATTER. 
335 
synchronism here suggests itself. These shorter waves are effectual because their motion 
is stored up. Their infinitesimal impulses, because imparted at the proper intervals, accu- 
mulate and finally become intense enough to jerk asunder the atoms with whose periods 
they are in accordance. 
§ II- 
The investigation which I have now the honour to offer to the Iloyal Society is in a 
certain sense complementary to those referred to at the outset of this paper. It deals 
with the relations of gaseous matter to the most refrangible rays of the spectrum. It 
treats of the chemical energies of such rays as exerted upon such matter. If we 
except the combination of chlorine and hydrogen by light, and the decomposition of 
carbonic acid by the solar rays in the leaves of plants, which latter, however, may not 
he the decomposition of a gas , no fact I believe has hitherto been known to exist in 
which light, or heat in the radiant form, acts chemically upon a gas or vapour*. By 
this inquiry the range of radiant energy as a chemical agent is considerably extended ; 
the phenomena resulting from that energy are exhibited in a new and exceedingly 
impressive form, and they prompt reflections regarding the possible influence of solar 
radiation on the gases, vapours, and effluvia of our atmosphere which could not previously 
be entertained. 
The inquiry was started thus : — It is known to the Society that the experiments on 
radiant heat already referred to, were for the most part performed in tubes of brass or 
glass, called for the sake of distinction “experimental tubes.” It is also known to the 
physical members of the Society that a difference f exists between my eminent friend 
Professor Magnus J and myself with regard to the deportment of aqueous vapour towards 
radiant heat. Last autumn, and in reference to the reasons assigned by him for this 
difference, I scrutinized the appearance of my experimental tubes during the entrance 
into them of various gases and vapours. The vapours were carried into the tubes by dry 
air which had been permitted to bubble through their liquids. I watched carefully, and 
with the aid of magnifying-lenses, for any signs of the precipitation of moisture either 
upon the surface of the experimental tube itself or upon the plates of rock-salt em- 
ployed to close it, keeping at the same time my eyes open to any other action which 
the intensely concentrated beam employed in the inquiry might reveal. 
On the 9th of October, 1868, while thus engaged upon the vapour of the nitrite of 
amyl, I observed a curious cloudiness in the experimental tube when the beam was sent 
through the vapour. For a moment this appearance troubled me; for it required a 
little reflection to assure me that in my previous publications I had not sometimes 
ascribed to pure cloudless vapour actions which were really due to such nebulous matter 
as was then before me. The appearance, however, immediately declared itself to my 
mind as a product of chemical action then and there exerted on the vapour. 
* Professor Stokes reminds me tliat Phosgen gas derives its name from its formation under the influence of 
light. — [J. T., July 1870.] f To be still cleared up. 
t Unhappily lost to science since these words were written. — [J. T., July 1870.] 
2 y 2 
