COAL FIELDS. 263 



To this statement there is but a single exception, and that an insig- 

 nificant one. When the tide rises highest upon the land, some little 

 portion of it can be arrested, and detained by dams and gates suitably 

 located. By opening the gates when the tide turns, the head of water 

 which has been secured can for a few hours turn wheels, grind grain, 

 saw lumber and execute other like offices. This force is, however, limited 

 to a very small portion of the earth's surface and is of small account at 

 the best. 



But every other form of force that men utilize, is directly or indirectly 

 referable to the sun. 



The wind is one of the natural forces that men learned to use long 

 ago in their migrations and their mechanical work, but it is the heat of 

 the sun that is the cause of every movement in the atmosphere. The 

 entire power of the winds is borrowed directly from the sun. 



The force of running water, applied also to transportation and 

 mechanical work, has been of larger service than the force of the wind. 

 What gives the running water its force? It is gravitation, as the water 

 descends the mountain side or the continental slope to the sea. But 

 how came the water upon the mountain side or the continental slope ? 

 Every drop that we find above the ocean level was lifted from the great 

 reservoir by the heat of the sun and borne to its destination by winds 

 that had the same origin. 



But the earliest force that man learned to use in the improvement 

 of his condition was the power of muscle. To the power of 

 his own muscle he soon added the patient strength of the animals 

 that he was able to subdue. 



From what source is muscular power derived? The animal world 

 is, in the last analysis, wholly dependent on the vegetable world and the 

 vegetable world is, in warp and woof, the direct product of the sun's 

 rays. All vital or living force can therefore be traced directly back to 

 the sun. 



But what of the great powers that are making over the world in our 

 time, viz., steam and electricity? Do not these forces of the modern 

 world come from a new source? By no means. It is the sun's power 

 that works in and originates both. The changing of water into steam 

 is the work of fuel, and as fuel is always organic in its origin, it must be 

 accounted for by the sun's rays as shown in the preceding paragraph. 

 For electricity, every current that we can utilize takes its rise either in 

 motion produced by steam or in the chemical changes of certain elements 

 and compounds, all of which are based ultimately on some form of carbon 

 derived from the vegetable world and therefore from the sun. 



How does this power of the sun become available to us? By what 

 process is the solar energy transformed into the power of muscle, steam 

 and electr'city? 



