294 THE ADDRESSES, LECTURES, ETC., OF 



which our life-sustaining food, both vegetable and animal, could 

 not be produced. 



When for our comfort and our use we resort to a fire either of 

 wood or coal, we know now by the light of modern science that 

 we are utilising only solar rays that have been stored up by the aid 

 of the process of vegetation in our forests or in the forests of 

 former geological ages, when our coal-fields were the scenes of rank 

 tropical growth. The potency of the solar ray in this respect was 

 recognised even before science had discovered its true signifi- 

 cance by clear-sighted men such as the late George Stephenson, 

 who, when asked what in his opinion was the ultimate cause of 

 the motion of his locomotive engine, said that he thought it went 

 by " the bottled-up rays of the sun." 



With the exception of our coal-fields and a few elementary 

 combustible substances such as sulphur and what are called the 

 precious metals, which we find sparsely scattered about, our earth 

 consists essentially of combined matter. Thus our rivers, lakes 

 and oceans are filled with oxidised hydrogen, the result of a most 

 powerful combustion ; and the crust of our earth is found to 

 consist either of quartz (a combination of the metal silicon with 

 oxygen) or limestone (oxidised calcium combined with oxidised 

 carbon), or of other metals, such as magnesium, aluminium, 

 or iron, oxidised and combined in a similar manner. 

 Excepting, therefore, the few substances before enumerated, we 

 may look upon our 'earth, near its surface at any rate, as a huge 

 ball of cinder, which, if left to itself, would soon become intensely 

 cold, and devoid of life or animation of any kind. 



It is true that a goodly store of heat still exists in the interior 

 of our earth, which according to some geologists is in a state of 

 fusion, and must certainly be in a highly heated condition ; but 

 this internal heat would be of no avail, owing to the slow rate 

 of conduction, by which alone, excepting volcanic action, it could 

 be brought to us living upon its surface. 



An estimate of the amount of heat poured down annually upon 

 the surface of our earth may be formed from the fact that it 

 exceeds a million times the heat producible by all the coal raised, 

 which may be taken at 280,000,000 tons a year. 



If then we depend upon solar radiation for our very existence 

 from day to day, it cannot be said that we are only remotely in- 



