348 FRAGMENTS OF SCIENCE 



The rays emitted by the current of hot air already referred 

 to were permitted to fall upon one of the faces of the pile; 

 and an extremely slight movement of the needle showed 

 that the radiation from the hot air, though sensible, was 

 extremely feeble. Connected with the ring-burner was a 

 holder containing oxygen gas; and by turning a cock, a 

 stream of this gas was permitted to issue from the burner, 

 strike the copper ball, and ascend in a heated column in 

 front of the pile. The result was, that oxygen showed 

 itself, as a radiator of heat, to be quite as feeble as at- 

 mospheric air. 



A second holder containing olefiant gas was then con- 

 nected with the ring-burner. Oxygen and air had already 

 flowed over the ball and cooled it in some degree. Hence 

 the olefiant gas labored under a disadvantage. But on 

 permitting the gas to rise from the ball, it cast an amount 

 of heat against the adjacent face of the pile sufficient to 

 impel the needle of the galvanometer almost to 90. This 

 experiment proved the vast difference between two equally 

 invisible gases with regard to their power of emitting ra- 

 diant heat. 



The converse experiment was now performed. The 

 thermo-electric pile was removed and placed between two 

 cubes filled with water kept in a state of constant ebulli- 

 tion; and it was so arranged that the quantities of heat 

 falling from the cubes on the opposite faces of the pile 

 were exactly equal, thus neutralizing each other. The 

 needle of the galvanometer being at zero, a sheet of oxy- 

 gen gas was caused to issue from a slit between one of the 

 cubes and the adjacent face of the pile. If this sheet of 

 gas possessed any sensible power of intercepting the ther- 

 mal rays from the cube, one face of the pile being de- 



