COAL AS A RESERVOIR OF POWER. 741 



principally carbonic acid, which result from this combustion. This 

 carbonic acid is inhaled by the plant ; and, by its vital power, excited 

 by sunshine, it is decomposed ; the carbon forms the ligneous structure 

 of the plant, and the oxygen is liberated to renew the healthful con- 

 dition of the atmosphere. Here we see a sequence of changes analo- 

 gous to those which have been shown to be a law of electricity. 



Every equivalent of matter changing form in the sun sends forth 

 a measured volume of sunshine, charged with the organizing powers 

 as potential energies. These meet with the terrestrial matter which 

 has the function of living, and they expend themselves in the labor of 

 producing a quantity of wood, which represents the equivalent of 

 matter which has changed form in the sun. The light, heat, chemical 

 and electrical power of the sunshine have produced a certain quantity 

 of wood, and these physical energies have been absorbed used up 

 in the production of that quantity. Now, we learn that a cube of 

 wood is the result of a fixed measure of sunshine ; common experience 

 teaches us that, if we ignite that wood, it gives out, in burning, light 

 and heat ; while a little examination proves the presence of actinism 

 and electricity in its flame. Philosophy teaches us that the powers 

 set free in the burning of that cube of wood are exactly those which 

 were required for its growth, and that, for the production of it, a 

 definite equivalent of matter changed its form on a globe ninety mill- 

 ions of miles distant from us.. 



Myriads of ages before man appeared the monarch of this world 

 the sun was doing its work. Vast forests grew, as they now grow, 

 especially in the wide-spread swamps of the tropics, and, decaying, 

 gathered into thick mats of humus-like substance. Those who have 

 studied all the conditions of a peat-morass, will remember how the 

 ligneous matter loses its woody structure in depth depth here rep- 

 resenting time and how at the bottom a bituminous or coaly matter 

 is not unfrequently formed. Some such process as this, continued 

 through long ages, at length produced those extensive beds of coal 

 which are so distinguishingly a feature of the British and American 

 coal-fields. At a period in geological time, when an Old Red Sand- 

 stone land was washed by ocean-waves highly charged with carbonic 

 acid, in which existed multitudinous animals, whose work in Nature 

 was to aid in the building up masses of limestone-rock, there prevailed 

 a teeming vegetation from which have been derived all the coal-beds of 

 the British Isles. Our space will not allow of any inquiry into the 

 immensity of time required for the growth of the forests necessary for 

 the production of even a single seam of coal. Suffice it to say that, 

 within one coal-field, we may discover coal-beds to the depth of G,000 

 feet from the present surface. The section of such a coal-field will 

 show us coal and sandstone, or shale, alternating again and again a 

 yard or two of coal and hundreds of feet of shale or sandstone until 

 we come to the present surface every one of those deeply-buried 



