At no time since men have dwelt upon the earth have their notions about the universe undergone so great a change as in the century of which we are now approaching the end. Never before has knowledge increased so rapidly; never before has philosophical speculation been so actively conducted, or its results so widely diffused. It is a characteristic of organic evolution that numerous progressive tendencies, for a long time inconspicuous, now and then unite to bring about a striking and apparently sudden change; or a set of forces, quietly accumulating in one direction, at length unlock some new reservoir of force and abruptly inaugurate a new series of phenomena, as when water rises in a tank until its overflow sets whirling a system of toothed wheels. It may be that Nature makes no leaps, but in this way she now and then makes very long strides. It is in this way that the course of organic development is marked here and there by memorable epochs, which seem to open new chapters in the history of the universe. There was such an epoch when the common ancestor of ascidian and amphioxus first showed rudimentary traces of a vertebral column. There was such an epoch when the air-bladder of early amphibians began to do duty as a lung. Greatest of all, since the epoch, still hidden from our ken, when organic life began upon the surface of the globe, was the birth of that new era when, through a wondrous change in the direction of the working of natural selection, Humanity appeared upon the scene. In the career of the human race we can likewise point to periods in which it has become apparent that an immense stride was taken. Such a period marks the dawning of human history, when after countless ages of desultory tribal warfare men succeeded in uniting into comparatively stable political societies, and through the medium of written language began handing down to posterity the record of their thoughts and deeds. Since that morning twilight of history there has been no era so strongly marked, no change so swift or so far-reaching in the conditions of human life, as that which began with the great maritime discoveries of the fifteenth century and is approaching its culmination to-day. In its earlier stages this modern era was signalized by sporadic achievements of the human intellect, great in themselves and leading to such stupendous results as the boldest dared not dream of. Such achievements were the invention of printing, the telescope and microscope, the geometry of Descartes, the astronomy of Newton, the physics of Huyghens, the physiology of Harvey. Man's senses were thus indefinitely enlarged as his means of registration were perfected; he became capable of extending physical inferences from the earth to the heavens; and he made his first acquaintance with that luminiferous ether which was by and by to reveal the intimate structure of matter in regions far beyond the power of the microscope to penetrate.

It is only within the present century that the vastness of the changes thus beginning to be wrought has become apparent. The scientific achievements of the human intellect no longer occur sporadically: they follow one upon another, like the organized and systematic conquests of a resistless army. Each new discovery becomes at once a powerful implement in the hands of innumerable workers, and each year wins over fresh regions of the universe from the unknown to the known. Our own generation has become so wonted to this unresting march of discovery that we already take it as quite a matter of course. Our minds become easily deadened to its real import, and the examples we cite in illustration of it have an air of triteness. We scarcely need to be reminded that all the advances made in locomotion, from the days of Nebuchadnezzar to those of Andrew Jackson, were as nothing compared to the change that has been wrought within a few years by the introduction of railroads. In these times, when Puck has fulfilled his boast and put a girdle about the earth in forty minutes, we are not yet perhaps in danger of forgetting that a century has not elapsed since he who caught the lightning upon his kite was laid in the grave. Yet the lesson of these facts, as well as of the grandmother's spinning-wheel that stands by the parlour fireside, is well to bear in mind. The change therein exemplified since Penelope plied her distaff is far less than that which has occurred within the memory of living men. The developments of machinery, which have worked such wonders, have greatly altered the political conditions of human society, so that a huge republic like the United States is now as snug and compact and easily manageable as the tiny republic of Switzerland in the eighteenth century. The number of men that can live upon a given area of the earth's surface has been multiplied manifold, and while the mass of human life has thus increased its value has been at the same time enhanced.

In these various applications of physical theory to the industrial arts, countless minds, of a class that formerly were not reached by scientific reasoning at all, are now brought into daily contact with complex and subtle operations of matter, and their habits of thought are thus notably modified. Meanwhile, in the higher regions of chemistry and molecular physics the progress has been such that no description can do it justice. When we reflect that a fourth generation has barely had time to appear on the scene since Priestley discovered that there was such a thing as oxygen, we stand awestruck before the stupendous pile of chemical science which has been reared in this brief interval. Our knowledge thus gained of the molecular and atomic structure of matter has been alone sufficient to remodel our conceptions of the universe from beginning to end. The case of molecular physics is equally striking. The theory of the conservation of energy, and the discovery that light, heat, electricity, and magnetism are differently conditioned modes of undulatory motion transformable each into the other, are not yet fifty years old. In physical astronomy we remained until 1839 confined within the limits of the solar system, and even here the Newtonian theory had not yet won its crowning triumph in the discovery of the planet Neptune. To-day we not only measure the distances and movements of many stars, but by means of spectrum analysis are able to tell what they are made of. It is more than a century since the nebular hypothesis, by which we explain the development of stellar systems, was first propounded by Immanuel Kant, but it is only within thirty years that it has been generally adopted by astronomers; and among the outward illustrations of its essential soundness none is more remarkable than its surviving such an enlargement of our knowledge. Coming to the geologic study of the changes that have taken place on the earth's surface, it was in 1830 that Sir Charles Lyell published the book which first placed this study upon a scientific basis. Cuvier's classification of past and present forms of animal life, which laid the foundations alike of comparative anatomy and of palÆontology, came but little earlier. The cell-doctrine of Schleiden and Schwann, prior to which modern biology can hardly be said to have existed, dates from 1839; and it was only ten years before that the scientific treatment of embryology began with Von Baer. At the present moment, twenty-six years have not elapsed since the epoch-making work of Darwin first announced to the world the discovery of natural selection.

In the cycle of studies which are immediately concerned with the career of mankind, the rate of progress has been no less marvellous. The scientific study of human speech may be said to date from the flash of insight which led Friedrich Schlegel in 1808 to detect the kinship between the Aryan languages. From this beginning to the researches of Fick and Ascoli in our own time, the quantity of achievement rivals anything the physical sciences can show. The study of comparative mythology, which has thrown such light upon the primitive thoughts of mankind, is still younger,—is still, indeed, in its infancy. The application of the comparative method to the investigation of laws and customs, of political and ecclesiastical and industrial systems, has been carried on scarcely thirty years; yet the results already obtained are obliging us to rewrite the history of mankind in all its stages. The great achievements of archÆologists—the decipherment of Egyptian hieroglyphs and of cuneiform inscriptions in Assyria and Persia, the unearthing of ancient cities, the discovery and classification of primeval implements and works of art in all quarters of the globe—belong almost entirely to the nineteenth century. These discoveries, which have well-nigh doubled for us the length of the historic period, have united with the quite modern revelations of geology concerning the ancient glaciation of the temperate zones, to give us an approximate idea of the age of the human race[1] and the circumstances attending its diffusion over the earth. It has thus at length become possible to obtain something like the outlines of a comprehensive view of the history of the creation, from the earliest stages of condensation of our solar nebula down to the very time in which we live, and to infer from the characteristics of this past evolution some of the most general tendencies of the future.

All this accumulation of physical and historical knowledge has not failed to react upon our study of the human mind itself. In books of logic the score of centuries between Aristotle and Whately saw less advance than the few years between Whately and Mill. In psychology the work of Fechner and Wundt and Spencer belongs to the age in which we are now living. When to all this variety of achievement we add what has been done in the critical study of literature and art, of classical and Biblical philology, and of metaphysics and theology, illustrating from fresh points of view the history of the human mind, the sum total becomes almost too vast to be comprehended. This century, which some have called an age of iron, has been also an age of ideas, an era of seeking and finding the like of which was never known before. It is an epoch the grandeur of which dwarfs all others that can be named since the beginning of the historic period, if not since Man first became distinctively human. In their mental habits, in their methods of inquiry, and in the data at their command, "the men of the present day who have fully kept pace with the scientific movement are separated from the men whose education ended in 1830 by an immeasurably wider gulf than has ever before divided one progressive generation of men from their predecessors."[2] The intellectual development of the human race has been suddenly, almost abruptly, raised to a higher plane than that upon which it had proceeded from the days of the primitive troglodyte to the days of our great-grandfathers. It is characteristic of this higher plane of development that the progress which until lately was so slow must henceforth be rapid. Men's minds are becoming more flexible, the resistance to innovation is weakening, and our intellectual demands are multiplying while the means of satisfying them are increasing. Vast as are the achievements we have just passed in review, the gaps in our knowledge are immense, and every problem that is solved but opens a dozen new problems that await solution. Under such circumstances there is no likelihood that the last word will soon be said on any subject. In the eyes of the twenty-first century the science of the nineteenth will doubtless seem very fragmentary and crude. But the men of that day, and of all future time, will no doubt point back to the age just passing away as the opening of a new dispensation, the dawning of an era in which the intellectual development of mankind was raised to a higher plane than that upon which it had hitherto proceeded.

As the inevitable result of the thronging discoveries just enumerated, we find ourselves in the midst of a mighty revolution in human thought. Time-honoured creeds are losing their hold upon men; ancient symbols are shorn of their value; everything is called in question. The controversies of the day are not like those of former times. It is no longer a question of hermeneutics, no longer a struggle between abstruse dogmas of rival churches. Religion itself is called upon to show why it should any longer claim our allegiance. There are those who deny the existence of God. There are those who would explain away the human soul as a mere group of fleeting phenomena attendant upon the collocation of sundry particles of matter. And there are many others who, without committing themselves to these positions of the atheist and the materialist, have nevertheless come to regard religion as practically ruled out from human affairs. No religious creed that man has ever devised can be made to harmonize in all its features with modern knowledge. All such creeds were constructed with reference to theories of the universe which are now utterly and hopelessly discredited. How, then, it is asked, amid the general wreck of old beliefs, can we hope that the religious attitude in which from time immemorial we have been wont to contemplate the universe can any longer be maintained? Is not the belief in God perhaps a dream of the childhood of our race, like the belief in elves and bogarts which once was no less universal? and is not modern science fast destroying the one as it has already destroyed the other?

Such are the questions which we daily hear asked, sometimes with flippant eagerness, but oftener with anxious dread. In view of them it is well worth while to examine the idea of God, as it has been entertained by mankind from the earliest ages, and as it is affected by the knowledge of the universe which we have acquired in recent times. If we find in that idea, as conceived by untaught thinkers in the twilight of antiquity, an element that still survives the widest and deepest generalizations of modern times, we have the strongest possible reason for believing that the idea is permanent and answers to an Eternal Reality. It was to be expected that conceptions of Deity handed down from primitive men should undergo serious modification. If it can be shown that the essential element in these conceptions must survive the enormous additions to our knowledge which have distinguished the present age above all others since man became man, then we may believe that it will endure so long as man endures; for it is not likely that it can ever be called upon to pass a severer ordeal.

All this will presently appear in a still stronger light, when we have set forth the common characteristic of the modifications which the idea of God has already undergone, and the nature of the opposition between the old and the new knowledge with which we are now confronted. Upon this discussion we have now to enter, and we shall find it leading us to the conclusion that throughout all possible advances in human knowledge, so far as we can see, the essential position of theism must remain unshaken.