RADIATION. 35 



tion of every pipe and string, so does the inter-stellar 

 ether accommodate itself to the requirement of light and 

 heat. Its waves mingle in space without disorder, each 

 being endowed with an individuality as indestructi- 

 ble as if it alone had disturbed the universal re- 

 pose. 



All vagueness with regard to the use of the terms 

 ' radiation ' and ' absorption ' will now disappear. Ra- 

 diation is the communication of vibratory motion to 

 the ether; and when a body is said to be chilled by 

 radiation, as for example the grass of a meadow on a 

 starlight night, the meaning is, that the molecules of 

 the grass have lost a portion of their motion, by im- 

 parting it to the medium in which they vibrate. On 

 the other hand, the waves of ether may so strike against 

 the molecules of a body exposed to their action as to 

 yield up their motion to the latter; and in this transfer 

 of the motion from the ether to the molecules consists 

 the absorption of radiant heat. All the phenomena 

 of heat are in this way reducible to interchanges of mo- 

 tion; and it is purely as the recipients or the donors of 

 this motion, that we ourselves become conscious of the 

 action of heat and cold. 



3. The Atomic Theory in reference to the Ether. 



The word * atoms ' has been more than once em- 

 ployed in this discourse. Chemists have taught us that 

 all matter is reducible to certain elementary forms to 

 which they give this name. These atoms are endowed 

 with powers of mutual attraction, and under suitable 

 circumstances they coalesce to form compounds. Thus 

 oxygen and hydrogen are elements when separate, or 

 merely mixed, but they may be made to combine so as 



