RADIATION OF HEAT BY GASEOUS AND LIQUID MATTER. 
219 
Carbonic oxide . ® 28’0 
Carbonic acid 33-6 
Nitrous oxide 44 '5 
Olefiant gas 68-0 
Its proximity to the pile, and the fact of its having to cross but one plate of salt, 
makes the action of the second chamber much greater than that of the first. 
Each of the Tables exhibits the fact that as the length of the chamber increases the 
dynamic radiation of the gas contained in it increases, and as the length diminishes the 
radiation diminishes. We also see how powerfully the gas in the second chamber 
acts upon the radiation from the first. With carbonic oxide, the presence of the gas in 
the second chamber reduces the deflection from 13 0, 7 to 6°‘3 ; with carbonic acid it is 
reduced from 16-8 to 6‘6 ; with nitrous oxide it is reduced from 19-5 to 6’2. Now this 
residual deflection, 6 0, 2, is not entirely due to the transparency of the gas, to heat emitted 
by the gas. No matter how well polished the experimental tube may be, there is always 
a certain radiation from its interior surface when the gas enters it. With perfectly 
dry air this radiation amounts to 8 or 9 degrees. Thus the radiation is composite, in 
part emanating from the molecules in the first chamber, and in part emanating from 
the surface of the tube. To these latter, the gas in the second chamber would be 
much more permeable than to the former ; and to these latter, I believe, the residual 
deflection of 6 degrees, or thereabouts, is mainly due. That this number turns up so 
often, although the radiations from the various gases differ considerably, is in harmony 
with the supposition just made. In the case of carbonic oxide, for example, the deflec- 
tion is reduced from 13 0, 7 to 6°*3, while in the case of nitrous oxide it is reduced from 
19°*5 to 6°-2 ; in the case of olefiant gas it is reduced from 59° to 10°*4, while in other 
experiments (not here recorded) the deflection by olefiant gas was reduced from 44° 
to 6°. 
As may be expected, this radiation from the interior surface augments with the 
tarnish of the surface, but the extent to which it may be increased is hardly sufficiently 
known. Indeed the gravest errors are possible in experiments of this nature if the 
influence of the interior be overlooked or misunderstood. An experiment or two will 
illustrate this more forcibly than any words of mine. 
A brass tube 3 feet long, and very slightly tarnished within, was used for dynamic 
radiation. Dry air on entering the tube produced a deflection of 12 degrees. The 
tube was then polished within, and the experiment repeated ; the action of dry air was 
instantly reduced to 7-5 degrees. 
The rock-salt plate at the end of the tube was then removed, and a lining of black 
paper 2 feet long was introduced within it. The tube was again closed, and the experi- 
ment of allowing dry air to enter it repeated. The deflections observed in three successive 
experiments were 
80°, 81°, 80°. 
This result might be obtained as long as the lining continued within the tube. 
