9,6 Mr. Brande on the composition and analysis 
sible to the hand, and in depressing and elevating the flame 
by means of a regulating stopcock, corresponding effects were 
produced upon the thermometer : the lens itself, which was a 
thick one, did not become heated. 
These experiments coincide in result with those of Dr. 
Maycock, and of M. Delaroche,* and show that the calo- 
rific rays emanating from common combustibles, are capable 
of passing through transparent media like those of the sun. 
10. There are certain substances, the chemical relations of 
which are singularly affected by the influence of direct solar 
rays. Among these, the mixture of chlorine and hydrogen 
is most remarkable : if kept in common daylight, but out of 
direct sunshine, the gases do not act upon each other ; but 
the moment the mixture is placed in the sunshine, the muriatic 
acid begins to be formed. I therefore hoped that this property 
might be applicable in certain photometrical experiments. I 
exposed a mixture of equal volumes of chlorine and hydrogen, 
in a tube inverted over water, capable of holding about four 
cubical inches, and blown into a thin bulb at its upper ex- 
tremity, to the brilliant focus produced by a large olefiant 
gas flame; it was exposed for 15', but underwent no other 
change than a slight increase of bulk, acting as an air ther- 
mometer. 
11. It now occurred to me to try how far any effect would 
be produced by the more intense light of the Voltaic battery, 
and I placed the tube containing the mixed gases in a darkened 
room, within about an inch of the charcoal points connected 
with an apparatus of one hundred pairs of plates highly 
* Murray’s System of Chemistry, Vol. I. p. 336. 4th. Edition. 
