40 FKAGMENTS OF SCIENCE. 



in the most unexpected manner the influence of chemi- 

 cal combination. Thus the elementary gases, oxygen, 

 hydrogen, and nitrogen, and the mixture atmospheric 

 air, prove to be practical vacua to the rays of heat ; 

 for every ray, or, more strictly speaking, for every 

 unit of wave-motion, which any one of them inter- 

 cepts, perfectly transparent ammonia intercepts 5,460 

 units, olefiant gas 6,030 units, while sulphurous 

 acid gas absorbs 6,480 units. What becomes of the 

 wave-motion thus intercepted ? It is applied to the 

 heating of the absorbing gas. Through air, oxygen, 

 hydrogen, and nitrogen, the waves of ether pass with- 

 out absorption, and these gases are not sensibly changed 

 in temperature by the most powerful calorific rays. The 

 position of nitrous oxide in the foregoing table is 

 worthy of particular notice. In this gas we have the 

 same atoms in a state of chemical union, that exist 

 uncombined in the atmosphere ; but the absorption of 

 the compound is 1,800 times that of air. 



5. Formation of Invisible Foci. 



This extraordinary deportment of the elementary 

 gases naturally directed attention to elementary bodies 

 in other states of aggregation. Some of Melloni's re- 

 sults now attained a new significance. This celebrated 

 experimenter had found crystals of sulphur to be highly 

 pervious to radiant heat ; he had also proved that 

 lamp-black, and black glass, (which owes its blackness 

 to the element carbon) were to a considerable extent 

 transparent to calorific rays of low refrangibility. These 

 facts, harmonising so strikingly with the deportment of 

 the simple gases, suggested further enquiry. Sulphur 

 dissolved in bisulphide of carbon was found almost per- 



