60 Royal Society :— 
while little or no chemical action took place in the battery ; on heating 
the potassa, the character of the stratifications gradually changed, and 
suddenly a remarkably brilliant white discharge, also stratified, was 
observed ; intense chemical action was at the same time perceptibly 
taking place in the battery, and on breaking the circuit, the usual vivid 
electrical flame-discharge was developed at the point of disruption. 
The continuation of these experiments will necessarily occupy much 
time, involving, as they do, the charging of so extended a series of 
the nitric acid battery, and with the requisite care necessary for 
the proper insulation of each cell. Other phenomena were observed 
which require further verification ; but I hope that after the recess the 
result which I hope to obtain may be of sufficient interest to form the 
subject of a future communication. 
“Note on the Transmission of Radiant Heat through Gaseous 
Bodies.” By John Tyndall, Ph.D., F.R.S. &e. 
Before the Royal Society terminates fits present session, I am 
anxious to state the nature and some of the results of an investiga- 
tion in which I am now engaged. 
With the exception of the celebrated memoir of M. Pouillet on Solar 
Radiation through the atmosphere, nothing, so far.as I am aware, 
has been published on the transmission of radiant heat through 
gaseous bodies. We know nothing of the effect even of air upon 
heat radiated from terrestrial sources. 
The law of inverse squares has been proved by Melloni to be 
true for radiant heat passing through air, whence that eminent 
experimenter inferred that the absorption of such heat by the atmo- 
sphere, in a distance of 18 or 20 feet, is totally inappreciable. 
With regard to the action of other gases upon heat, we are not, so 
far as I am aware, possessed of a single experiment. 
Wishing to add to our knowledge in this important particular, I 
had a tube constructed, 4 feet long and 3 inches in diameter, and 
by means of brass terminations and suitable washers, I closed per- 
fectly the ends of the tube by polished plates of rock-salt. Near to 
one of its extremities, a T-piece is attached to the tube, one of 
whose branches can be screwed to the plate of an air-pump, so as to 
permit the tube to be exhausted ; while the gas to be operated on is 
admitted through the other branch of the T-piece. Such a tube 
can be made the channel of calorific rays of every quality, as the 
rock-salt transmits all such rays with the same facility. 
I first permitted the obscure heat emanating from a source placed 
at one end of the tube, to pass through the latter, and fall upon a 
thermo-electric pile placed at its other end. The tube contamed 
ordinary air. When the needle of a galvanometer connected with 
the pile had come to rest, the tube was exhausted, but no change in 
the position of the needle was observed. A similar negative result 
was obtained when hydrogen gas and a vacuum were compared. 
Here I saw, however, that when a copious radiation was employed, 
and the needle pointed to the high degrees of the galvanometer, to 
cause it to move through a sensible space, a comparatively large 
