44 FRAGMENTS OF SCIENCE 



quantities of heat are imparted to the two faces, the needle 

 points to zero. Let any gas be now permitted to enter the 

 exhausted tube; if its molecules possess any power of in- 

 tercepting the calorific waves, the equilibrium previously 

 existing will be destroyed, the compensating source will 

 triumph, and a deflection of the magnetic needle will be 

 the immediate consequence. Prom the deflections thus 

 produced by different gases we can readily deduce the 

 relative amounts of wave-motion which their molecules 

 intercept. 



In this way the substances mentioned in the following 

 table were examined, a small portion only of each being 

 admitted into the glass tube. The quantity admitted in 

 each case was just sufficient to depress a column of mer- 

 cury associated with the tube one inch: in other words, 

 the gases were examined at a pressure of one-thirtieth of 

 an atmosphere. The numbers in the table express the 

 relative amounts of wave-motion absorbed by the respec- 

 tive gases, the quantity intercepted by atmospheric air 

 being taken as unity. 



Radiation through Gases 



Relative 

 Name of gas absorption 



Air . . . ;" '!' ;; : : ~"'. ... i 



Oxygen . . ; ' . . ; ' . . . . 1 



Nitrogen . . f ..'.,.. . . . 1 



Hydrogen 1 



Carbonic oxide . . . x . . . . . 750 



Carbonic acid 972 



Hydrochloric acid * .1,005 



Nitric oxide 1,590 



Nitrous oxide 1,860 



Sulphide of hydrogen 2,100 



Ammonia . . .... 5,460 



Oleflant gas .... 6,030 



Sulphurous acid . ... 



