of our Earth than on the general subject of solar physics, yet illustrate in a significant manner the work which the Sun has been appointed to do. I may premise, indeed, that we have no means of determining what the Sun's influence on the other planets may be, however clear it may appear to us that we are not the only, nor even the chief, recipients of those stores of force he lavishes so abundantly. It is on this account that while I give to this treatise a title indicating the Sun's position in the solar system, I deal only in this chapter-the sole one bearing on the Sun's officewith his position as our fire, light, and life. If in the considerations I am about to urge the Earth only seems concerned, it is none the less probable that results affecting the economy of the whole planetary scheme are in truth illustrated. We are accustomed to look upon the Earth as an inexhaustible storehouse whence all our wants may be supplied. Year after year we till the soil, and still there is no lack in the growth of all the vegetable productions needed by man; nor do our flocks and herds diminish, notwithstanding the enormous supplies of flesh-meat we are continually consuming. Taking the whole Earth, it is probable that the yearly produce of agricultural and pastoral labours increases at even a higher rate than that at which the human race is increasing, so that were man content, as in old times, to draw upon the Earth's stores for the supply of his ordinary wants, there would be little fear of that store being ever exhausted. But of late a change has passed over the aspect of the world. On every side a multitude of new inventions, and with them a multitude of new wants, are making their appearance. The stores which had been garnered up during long past ages of the Earth's history are being consumed with a rapidity which has already begun to alarm our men of science. It is true, indeed, that there is as yet little room for fearing that the terrestial storehouse will soon be cleared of its contents. Even if the coal-mines of the world should be exhausted, there are still other force supplies; and doubtless the present rate of consumption might be continued, or even an increased rate maintained, for a period which seems indefinitely long when compared with the short span of life allotted to man. But, after all, what are a thousand years, or even several thousand years, when viewed with reference to the history of the globe on which we live? If it could be shown that within two or three thousand years man will have exhausted all the stores of force which exist within the Earth, it surely might be urged with fairness that the present rate of consumption is unduly -selfishly great; that the wants of future races should be considered, and that a check should be put upon those processes of over-rapid advance on which we are in the habit of priding ourselves. Precisely as we should hold it to be blameworthy that a rich man should use, merely for purposes of luxury or convenience, that which could be shown to be absolutely essential to the existence of a large number of his fellow-men, so D D it might fairly be held to be wrong for the present inhabitants of the Earth to exhaust, in contrivances intended to add to the luxuries or conveniences of life, those stores which are absolutely necessary to the wellbeing of future races. In dealing, for example, with the question of terrestrial coal supplies, it will not suffice to point out that for a thousand or several thousand years they may be drawn upon as at present, or even more largely, without exhaustion. The thousand or thousands of years will pass as surely as those which have already passed, and the wants entailed by our wastefulness will be felt none the less, that for so many years there had been no failure in the supplies contained within the great terrestrial storehouse. What must be done, then, is to show that by the progress of that very course of events which results in the rapid use of those stores, the means will spring into existence of obtaining fresh and inexhaustible supplies. This is no idly speculative view, but the plain and obvious duty of the scientific world. Precisely as the superiority of civilised races over barbarous tribes is shown in nothing more clearly than in the fact that the former are not content, as the latter are, merely to supply the wants of the moment, or of a few days, but seek to make provision, not only for future years, but for the wants of their immediate descendants, so it behoves the leaders of the great movement which during the last few years has so greatly changed the aspect of the human race, to show the superiority of the new order of things by a careful provision for, and anticipation of, the wants of the races which will inhabit the Earth thousands of years hence. Without discussing the various forms of work which are being done upon the Earth, or considering the various agents employed in producing the motive power by which those forms of work are set in action, it may be simply stated that at present nearly all our motive force is obtained from stored Sun-force. It would be difficult to point to a single work accomplished by the aid of modern scientific appliances which has not resulted in exhausting to a greater or less degree the force which the Earth has been garnering up in long-past ages for our use. It is in this all-important respect that the more modern forms of machine-work differ from other forms of work. I refer, of course, to machines driven by inanimate motive powers, and not to those worked by the direct action of animal force. The machine draws upon the Earth's garnered stores, while the living worker draws upon the Earth's periodical supplies of force. In the former case, that is being used up which cannot be replaced; in the latter, what is consumed will be restored in the ordinary course of nature. In one case it is our force-principal,' in the other it is our 'force-income' we are consuming. The distinction is all-important. * Those appliances in which advantage is taken of the action of the wind, rainfall (rivers), tidal action, and a few other natural processes, are to be excepted. Modern invention, however, is but seldom directed to the utilisation of these old-fashioned force-supplies. This is not the place to enter into a discussion of the methods by which the great problem-a problem not requiring immediate solution, but which in the long run will surpass all others in interest and importance is to be solved. But I may indicate what is, I take it, the direction in which a solution will be found. We are now utilising what Professor Tyndall calls the Sun of the Carboniferous Epoch: our descendants will have to employ the Sun of their own epoch. The heat of the solar rays-mayhap also their light and their actinic energy-must one day be applied to work our machinery. Already men have felt the advantage of thus employing solar energy. They have not, indeed, as yet applied the direct action of the Sun systematically to their purposes. But in an indirect manner they have utilised solar energy. The ships which sail upon our seas, the mills which are turned by water or by wind-these and many other devices of man have been contrived to utilise a portion of the Sun's heat. But the proportion thus utilised is almost indefinitely small by comparison with that which is actually available. It is only necessary to translate some of the ordinary phenomena of nature into the language of the familiar forces in order to see that this is so. For instance, the amount of energy involved in the production of rain is startlingly great * Ericsson has constructed a machine in which the solar rays supply the primary motive force. It has not, however, yet been demonstrated (though I have not the least doubt it will be at some future epoch) that the solar heat can be employed in a profitable—that is, a mechanically advantageous,' manner. |