Radiation of Heat by Gases and Vapours. 279 



Fig. 1. 



observed, and the limit of the arc through which its needle was 

 urged was noted. It is needless to remark that the ball was 

 entirely hidden by the screen from the thermo-electric pile, 

 and that, even were this not the case, the mode of neutraliza- 

 tion 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 6 



Oxygen 



Nitrogen .... 



Hydrogen .... 



Carbonic oxide . . 12 



Carbonic acid . . . 18 



Nitrous oxide ... 29 



Olefiant gas ... 53 



The radiation from 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, hydro- 



* I have also rendered these experiments on radiation visible to a large 

 audience. They may be readily introduced in lectures on radiant heat. 



