200 FRAGMENTS OF SCIENCE. 



these molecules not as absorbers, but as radiators, not as 

 the recipients, but as the originators of wave motion. That 

 is to say, we must figure them vibrating and generating in 

 the surrounding ether undulations which speed through it 

 with the velocity of light. Our object now is to inquire 

 whether the act of chemical combination, which proves so 

 potent as regards the phenomena of absorption, does not 

 also manifest its power in the phenomena of radiation. For 

 the examination of this question it is necessary, in the first 

 place, to heat our gases and vapors to the same tempera- 

 ture, and then examine their power of discharging the 

 motion thus imparted to them upon the ether in which 

 they swing. 



A heated copper ball was placed above a ring gas- 

 burner possessing a great number of small apertures, the 

 burner being connected by a tube with vessels containing 

 the various gases to be examined. By gentle pressure the 

 gases were forced through the orifices of the burner against 

 the copper ball, where each of them, being heated, rose in 

 an ascending column. A thermo-electric pile, entirely 

 screened off from the hot ball, was exposed to the radiation 

 of the warm gas, and the deflection of a magnetic needle 

 connected with the pile declared the energy of the radia- 

 tion. 



By this mode of experiment it was proved that the self- 

 same molecular arrangement which renders a gas a power- 

 ful absorber, renders it in the same degree a powerful 

 radiator — that the atom or molecule which is competent to 

 intercept the calorific waves is in the same degree compe- 

 tent to generate them. Thus, while the atoms of element- 

 ary gases proved themselves unable to emit any sensible 

 amount of radiant heat, the molecules of compound gases 

 were shown to be capable of powerfully disturbing the sur- 

 rounding ether. By special modes of experiment the same 

 was proved to hold good for the vapors of volatile liquids, 



