tons one hundred feet, or 732,000,000 pounds one foot. I said, if wholly utilized, for, although we are able to make use of the whole energy in the form of heat, we have not yet succeeded in applying more than about one-twentieth of it to mechanical work. But still the energy exists stored up for use in every foot of wood or coal, and is ready to be set free when the fuel is burnt. When standing before a grand conflagration, witnessing the display of mighty energies there in action, and seeing the elements rushing into combination with a force which no human energy can withstand, does it seem as if any power could undo that work of destruction, and rebuild those beams and rafters which are melting into air? Yet, in a few years thay will be rebuilt. This mighty force will be overcome; not, however, as we might expect, amid the convulsions of Nature or the clashing of the elements, but silently in a delicate leaf waving in the sunshine. As I have already explained, the sun's rays are the Ithuriel wand, which exerts the mighty power, and under the direction of that unerring Architect, whom all true science recognizes, the woody structure will be rebuilt, and fresh energy stored away to be used or wasted in some future conflagration.

My friends, this is no theory, but sober, well-established fact. How the energy comes and how it is stored away, we attempt to explain by our theories. Let these pass. They may be true, they may be mere fancies; but, that the energy comes, that it is stored away, and that it does reappear, are as much facts as any phenomena which the sun's rays illuminate. I know of no facts in the whole realm of Nature more wonderful than these, and I return to them in the annual round of my instruction with increasing wonder and admira

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tion, amazed at the apparent inefficiency of the means, and the stupendous magnitude of the result. In another course of lectures in this place I endeavored to show what weighty evidence these facts give in support of the argument that all the details have been arranged by an intelligent Designer.' The plan of this course does not give me time to do more than allude to this point, and I only refer to it here to ask for the argument your own careful consideration.

There is still another point, in connection with this subject, to which also I can only barely allude. The crust of our globe consists almost wholly of burnt material. Our granite, sandstone, and limestone rocks, are the cinders of the great primeval fire, and the atmosphere of oxygen the residue left after the general conflagration-left because there was nothing more to burn. Whatever of combustible material, wood, coal, or metal, now exists on the surface of the earth, has been recovered from the wreck of the first conflagration by the action of the sun's rays. One-half of all known material consists of oxygen, and, on the surface of the globe, combination with oxygen is the only state of rest. In the process of vegetable growth, the sun's rays have the power of freeing from this combination hydrogen and carbon atoms, and from these are formed the numberless substances of which both the vegetable and animal organisms consist. From the material of these organisms we make charcoal, and Nature makes her coal-beds, and supplies her petroleum-wells. Moreover, with these same materials, man has been able to separate the useful metals from their ores, and, by the aid

1 "Religion and Chemistry; or, Proofs of God's Plan in the Atmosphere and its Elements,” ten lectures by Josiah P. Cooke, Jr., published by Charles Scribner. New York, 1864.

of various chemical processes, to isolate the other elementary substances from their native compounds; but the efficiency of all these processes depends on employing the energy which the sun's rays impart to the carbon and hydrogen atoms to do work. A careful analysis of the conditions will show that it is just as truly the sun's energy which parts the iron from its combination in the ore, as it is solar power which parts the carbon from the carbonic dioxide in the leaf. We have here, however, but a single example of a general truth. All terrestrial energy comes from the sun, and every manifestation of power on the earth can be traced directly back to his energizing and life-giving rays. The force with which oxygen tends to unite with the other elements may be regarded as a spring, which the sun's rays have the power to bend. In bending this spring they do a certain amount of work, and, when, in the process of combustion, the spring flies back, the energy reappears. Moreover, the instability of all organized forms is but a phase of the same action, and the various processes of decay, with the accompanying phenomenon of death, are simply the recoiling of the same bent spring. Amid all these varied phenomena, the one element which reappears in all, and frequently wholly engrosses our attention, is energy; and, if I have succeeded in fixing your attention on this point, my great object in this lecture has been gained. In the early part of this course, I stated that all modern chemistry rests on the great truth that MATTER IS INDESTRUCTIBLE, AND IS MEASURED BY WEIGHT. This evening we have seen glimpses of another great central truth, which, although more recently discovered, is not less far-reaching or important, namely, ENERGY IS INDESTRUCTIBLE, AND IS MEASURED BY WORK. Add to these

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two a third, namely-INTELLIGENCE IS INDESTRUCTIBLE, AND IS MEASURED BY ADAPTATION—and you have, as it seems to me, the three great manifestations of Nature: MATTER, ENERGY, and INTELLIGENCE. These great truths explain and supplement each other. Give to each its due weight in your philosophy, and you will avoid the extremes of idealism on the one side, and of materialism on the other.

LECTURE X.

GUNPOWDER AND NITRO-GLYCERINE.

THERE is one further point in connection with the theory of combustion to which I wish to call your attention, at the outset of my lecture this evening. In the only cases of burning we have studied, the combustible unites with the oxygen of the atmosphere. It is possible, however, to have combustion without atmospheric air, the combustible obtaining the required oxygen from some associated substance. There are several substances in which a large amount of oxygen is so loosely combined, or, in other words, in which the oxygen-atoms are held in combination by such a feeble force, that they will furnish oxygen to the combustible as readily as the atmosphere, and in a vastly more concentrated form. Two of these substances are well known, nitre (potassic nitrate) and chlorate of potash (potassic chlorate). One ounce of this last salt-the quantity in this small crucible-contains enough oxygen to fill a large jar (1.7 gallon), and by simply heating the salt we should obtain that amount of oxygen gas. We have provided also one-third of an ounce of pulverized sugar, and we will now mix the two powders thoroughly together. Consider the conditions in this