COAL AS A RESERVOIR OF POWER. 743 



equal to lifting 1,729,200 pounds one foot high. "We are raising every 

 year about 110,000,000 tons of coal from our coal-beds, each ton of 

 coal being about a square yard. The beat of that coal is equal to a 

 mechanical lifting power which it is scarcely possible to convey to the 

 mind in any thing approaching to its reality. If we say it is 190,212,- 

 000 millions we merely state an incomprehensible number. We may 

 do something more than this, if we can convey some idea of the mag- 

 nitude of the mass of coal which is raised annually in these islands. 



The diameter of this globe is 7,926 miles, or 13,880,760 yards; 

 therefore the coal raised in 1870 would make a solid bar more than 

 eight yards wide and one yard thick, which would pass from east to 

 west through the earth at the equator. Supposing such a mass to be 

 in a state of ignition, we can perhaps imagine the intensity of its heat, 

 and its capability, if employed in converting water into steam, of ex- 

 erting the vast force which we have endeavored to indicate. It was 

 intimated last year in the House of Commons by a member of the coal 

 commission that the decision of that body, after a long and laborious 

 inquiry, would be that there existed in our coal-fields a supply for 

 about one thousand years at our present rate of consumption. We 

 have therefore to multiply the above computation by 1,000 to arrive 

 at any idea of the reserved power of our British coal-fields. What 

 must it have been ei*e yet our coal deposits were disturbed ! At the 

 time of the Roman occupation coal was used in this country. In the 

 ruins of Roman Uriconium coal has been found. Certainly up to the 

 present time a quantity of not less than three thousand million tons of 

 coal has been dug oivt of our carboniferous deposits and consumed. 

 All this enormous mass of matter has been derived from vegetable or- 

 ganizations which have been built up by sunshine. The sun-rays 

 which compelled the plants to grow were used by the plant, absorbed, 

 imprisoned in the cells, and held there as an essential ingredient of the 

 woody matter. The heat, light, actinism, and electricity, which are 

 developed when we burn a lump of coal, represent exactly the quantity 

 of those forces Avhich were necessary to the growth of the vegetable 

 matter from which that coal was formed. The sunshine of infinitely 

 remote ages becomes the useful power of the present day. 



Let it not, however, be supposed that we employ all the heat which 

 is available in our coal. All our appliances, even the very best, are 

 so defective that we lose far more than we use. A pound of pure coal 

 should evaporate thirteen pounds of water ; in practice a pound of coal 

 does not evaporate four pounds, even in the most perfectly-constructed 

 steam-boilers, with the most complete steam-engines, such as have 

 been constructed for pumping water for the Chelsea and the other wa- 

 ter-works upon the Thames. 



Numerous attempts have been made to burn our coal so as to se- 

 cure a more effective result than this. There has been some advance, 

 the most satisfactory being in the regenerative furnace of Mr. Siemens. 



