equivalent to the requisite liberation of force necessary to reduce the gases back again to the solid form of ice. A cubic foot of water yields 1,862 cubic feet of the separate gases when at normal condition, and no human device is competent to overcome this expansion by pressure sufficient to reduce them back again to the liquid condition. Upon the evidence of Faraday we have it that "the decomposition of a single drop of water by electricity calls for an expenditure of more electromotive force than would suffice to charge a thunder-cloud."
Our main source of dynamic energy is from the sun. His energy is exhibited in every wind that blows, in every shower that falls, and in the history of every snow-flake—in the glare of gaslights, in the heat of the furnace, in the colors of the rainbow, and in the gorgeous sunset, in the beauty of vegetation and its silent growth. Thus, in an almost infinite variety of physical phenomena we see this transmutation of solar energy. This energy, after doing its allotted work, is in time dissipated into space by radiation. And, were it not for the intermediate position of the vegetable kingdom to check this degradation of energy and raise the elementary constituents from the chemical to the organic plane, man's duration here would be short indeed. The locking up of potential energy in the protoplasmic cell of the plant requires the expenditure of a vast amount of energy, but the solar ray, aided by the subtile alchemy of the leaf, is competent for the task; and, while the chlorophyl of the leaf assists in weaving organic tissues from the air, this outward dissipation of energy is delayed for a while, giving us food for our bodies and fuel for our fires. This final process of combustion once more converts these potential energies into the dynamic form and sets them free to dissipate into space. All the mechanical power which comes from the combustion of fuel and all the muscular force of the animal kingdom is but the transmutation of solar energy through the mediumship of plant-life. Well might we say, as did the pagans of old, "We are children of the sun." This flood of solar force is unceasing. Waves of ether may conduct a store of energies across the universe and invest them in a wealth of carbonaceous flora; these energies may lie dormant in vegetable fossils for untold eras; man may delve in mines and exhume the coal, and enlist the aid of oxygen to break the bonds of chemical affinity, setting free those energies stored away in the countless ages of the past; he may unfold link after link of the great dynamic chain of causation, and subject them to the scrutinizing analysis of the physicist; he may survey the rocks and tell us of their radiations of internal heat, or by his calculus tell us for how long in the past this planet may have been the theatre of life and death; he may tell us, not only of the energies in the atoms of a drop of water, but of a world of atoms—nay, more, of a universe made up of atoms with their energies drifting out into measureless space; but he can tell us naught of that unseen universe into which the energies of the visible creation are ever tending.
