100 Prof. Tyndall on the Absorption and Radiation 



The gases, it will be observed, exhibit a gradually increasing 

 power of dynamic radiation from carbonic oxide up to olefiant 

 gas. This is most clearly illustrated by reference to the results 

 obtained in the respective cases with the first length of the 

 second chamber. They are as follows : — 



o 



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 pre- 

 sence of the gas in the second chamber reduces the deflection 

 from 13°* 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°*2, is not entirely due to the transpa- 

 rency 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 mole- 

 cules in the first chamber, and in part emanating from the sur- 

 face of the tube. To these latter, the gas in the second cham- 

 ber 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 con- 

 siderably, is in harmony with the supposition just made. In 

 the case of carbonic oxide, for example, the deflection is reduced 

 from 13°*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 o, 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. 



