40 FRAGMENTS 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 intercepts, per- 

 fectly transparent ammonia intercepts 5,460 units, 

 olefiant gas 6,030 units, while sulphurous acid gas ab- 

 sorbs 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 without absorption, 

 and these gases are not sensibly changed in tempera- 

 ture 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 trans- 

 parent 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- 



