\\~n.i.iAM //:.!//:. v\, I-.R.S. 91 



into its elements carbon and oxygen, the oxygen being returned to 

 the atmosphere, and the carbon retained to form the solid substance 

 of the tree. 



Solar Energy in Fwl.The suii thus imparts 11,000,000 units 

 of energy to the tree for the formation of one pound of carbon in 

 the shape of woody fibre, and these 11,000,000 units of energy 

 will be simply resuscitated when the wood is burnt, or again 

 combined with oxygen to form carbonic acid. 



Fuel, then, is derived through solar energy acting on the surface 

 of our earth. 



But what about the stores of mineral fuel, of coal, which we 

 find within its folds ? How did they escape the general combus- 

 tion which, as we have seen, has consumed all other elementary 

 substances ? The answer is a simple one. These deposits of 

 mineral fuel are the results of primeval forests, formed in the 

 manner of to-day through the agency of solar rays, and covered 

 over with earthy matter in the many inundations and convulsions 

 of the globe's surface, which must have followed the early solidifi- 

 cation of its surface. Thus our deposits of coal may be looked 

 upon as the accumulation of potential energy derived directly 

 from the sun in former ages, or as George Stephenson, with a 

 sagacity of mind in advance of the science of his day, answered, 

 when asked what was the ultimate cause of motion of his loco- 

 motive engine, " that it went by the bottled-up rays of the sun." 



It follows from these considerations that the amount of potential 

 energy available for our use is confined to our deposits of coal, 

 which, as appears from the exhaustive enquiries lately made by 

 the Royal Coal Commission are still large indeed, but by no means 

 inexhaustible, if we bear in mind that our requirements will be 

 ever on the increase and that the getting of coal will become from 

 year to year more difficult as we descend to greater depths. To 

 these stores must be reckoned lignite and peat, which, although 

 not coal, are nevertheless the result of solar energy, attributable to 

 a period of the earth's creation subsequent to the formation of the 

 coal beds, but anterior to our own days. These fuels may be made 

 as efficient as coal if properly treated. 



In discussing the necessity of using our stores of fuel more 

 economically, I have been met by the observation that we need 

 Hot be anxious about leaving fuel for our descendants that the 



