EADIATION OF HEAT BY GASES AND VAPOUES. 
31 
and that even were this not the case, the mode of neutralization adopted would still 
give us the pure action of the gas. 
The results of the experiments are given in the following Table, the figure appended 
to the name of each gas marking the number of degrees through which the radiation 
from the latter urged the needle of the galvanometer * : — 
Air .... 
. . . 0 
Oxygen . . . 
. . . 0 
Nitrogen 
. . . 0 
Hydrogen . . 
. . . 0 
Carbonic oxide 
... 12 
Carbonic acid . 
... 18 
Nitrous oxide . 
... 29 
Olefiant gas 
... 53 
The radiation fr-om air, it will be remembered, was neutralized by the large Leslie’s cube, 
and hence the 0° attached to it merely denotes that the propulsion of air from the gas- 
holder through the argand burner did not augment the effect. Oxygen, hydrogen, and 
nitrogen, sent in a similar manner over the ball, were equally ineffective. The other 
gases, however, not only exhibit a marked action, but also marked differences of action. 
Their radiative powers follow precisely the same order as their powers of absorption. 
In fact, the deflections actually produced by their respective absorptions at 5 inches 
tension are as follow : — 
Air 
A fraction of a degree 
Oxygen .... 
?? 
Nitrogen . . 
?? 5 ? 
Hydrogen . 
99 99 
Carbonic oxide 
O 
GO 
Carbonic acid . . 
... 25° 
Nitrous oxide . . 
. . . . 44° 
Olefiant gas 
... 61° 
It would be easy to give these experiments a more elegant form, and to arrive at 
greater accuracy, which I intend to do on a future occasion, but my object now is simply 
to establish the general order of their radiative powers. An interesting way of exhi- 
biting both radiation and absorption is as follows: — When the polished face of a 
Leslie’s cube is turned towards a thermo-electric pile the effect produced is inconsider- 
able, but it is greatly augmented when a coat of varnish is laid upon the polished surface. 
Instead of the coat of varnish, a film of gas may be made use of. Such a cube, con- 
taining boding water, had its polished face turned towards the pile, and its effect on 
* I have also rendered these experiments on radiation visible to a large audience. They may be readily 
introduced in lectures on radiant heat. 
