This work is not presented to the reader as a treatise on astronomy, although the different phenomena pertaining to that splendid science are reviewed with some detail, and the established facts bearing upon the subjects discussed are briefly cited in the very words of the great writers upon whose authority they rest. A considerable experience in chemistry, electricity, and the other allied physical sciences long since convinced the author of this work that some simple and uniform principle must control the production of the physical phenomena of astronomy,—some general law capable of being extended in its application to the widest, as well as applied to the narrowest, limits of that science. Knowing the absolute certainty of a magnetic and electrical connection between the sun and the earth, as evidenced by the reflected energy of sun-spots, auroras, etc., and that no known cause except electricity could account for some, at least, of the cometic phenomena, it seemed that any comprehensive law must at all events include this mode of energy as an effective cause, and that if the law be uniform in its application, it must equally exclude all others which may be either antagonistic or not necessary. A careful investigation was therefore made of those less generally known principles concerned in the generation and transformations of electrical energy, in order to determine the sufficiency or insufficiency of this agency in the grander operations of nature (for, of course, mere currents of electricity could play no part in these phenomena), with the result that every line of research led irresistibly to the conclusions presented in this work. These investigations, specifically directed, at first, to the source and mode of the solar energy of our own system alone, were found to be equally applicable to others, and were successively extended to the whole sidereal, nebular, and cometic field, and finally to space itself, for all the phenomena of which it seemed to furnish an adequate and harmonious interpretation. The fact, when once demonstrated, that the true source of solar energy is not to be found in the sun itself, but in the potential energy of space, served as a guiding principle, and, by its continuously extended application, was found to cover perfectly the source and mode of all solar energy. Every step of the investigation has been based on the established facts of science and the observations of eminent astronomers as laid down by the best authorities; and the quotations herein made from their works are full and fair, and are properly credited in every case, and taken from books easily accessible to the general reader. It is hoped that further attention may be directed to this field of research by far more capable investigators than the author of this work, so that systematic astronomy may no longer bear the reproach that it is largely an empirical science, but that it may henceforth be based upon rational and comprehensive principles, capable of universal extension and of general scientific application.

The authorities cited in this work include many illustrious names: Proctor, Tyndall, Helmholtz, Langley, Huggins, Newcomb, Young, Flammarion, Balfour Stewart, R. Kalley Miller, Herschel, Nichol, Lord Rosse, Urbanitsky, Crookes, Fraunhofer, Ball, and many others, all of whom are known throughout the world as among the master minds of science. From them we have drawn the rich stores of knowledge of the phenomena with which this work deals, and which we have so fully and freely cited, as the basis of the splendid superstructure which astronomy to-day reveals. No one will venture to controvert the statements of fact made by these eminent men, and, where conflict of opinion has arisen among them, we have quoted all parties, so that the reader can form his own conclusion, in each case, for himself. So diverse, apparently, are the phenomena reviewed that they present the aspect of a great picture-gallery, in which the paintings totally differ from each other in subject, in treatment, and in origin, their only common qualities being those of grandeur and fidelity to truth and to the principles of art. But they are not merely paintings, they are the moving panorama of creation, and, diverse as they may appear, they will be found to show the same “handling,” which reveals the same universal artist; they have, in truth, a common mode of development and a common principle of construction, obscure as these may seem to be.

For thousands of years “Natural History,” so called, was studied and taught; zoÖlogy was a well-known science far back in old historic times. But it was left for modern biological research to turn from these fixed and fully-developed forms of life, and go back to trace their primal development through what is now the science of embryology, and thus we have learned that nature traverses the same paths in forming a man as in producing a frog or a bird. The process is carried further along in one case than in another, but the lines of development are almost identical; and the tracing out of these common lines and their subsequent divergencies has shed a flood of new light upon these dark and hitherto unknown places, so that we are now fairly on the true highway of physical life at last. When adult forms were alone compared, animal with animal, no common ground of origin or development could be discerned; nature was believed to work by “special creations,” and vast cataclysms were devised to utterly destroy the organic life of one terrestrial epoch after another, leaving a few hardy accidental survivors, or “types,” perchance, to trace back their lines of descent beyond such periods of cyclical destruction. All this is now changed, and these views, so recently held and taught, have been abandoned forever, and continuously operative natural processes of development, modified by environment and heredity, have taken their place, and biology now has a future as well as a past. And so it must be with the less complex, but far more extended, creations and transformations in the vast fields of astronomical science with which this book is concerned. Hitherto we have here, too, dealt with “special creations” and cataclysms; henceforth we must follow the uniform and eternal laws of progressive development.

Among the multitude of hitherto unsolved problems of astronomy we may enumerate the following: Why sun-spots travel faster around the sun when near his equator than when more distant from it. The physical causes of sun-spots, faculÆ, and solar prominences. Why the number and size of sun-spots seem to affect terrestrial magnetism. The rational interpretation of the eleven-year and the long sun-spot cycles. The origin of the aurora borealis. The causes of the periodicity of regularly variable stars. How to explain, in accordance with the nebular hypothesis, why Algol and its companion, which are not greatly different in mass and volume, and both obviously gaseous, should so differ in character, one being a bright sun and the other a dark planet. Whether there are great, compact, but dark bodies, comparable to suns and planets in magnitude, and unconnected with any solar system, floating about in space. Why double and multiple stars are so frequently of contrasted or complementary colors. Why regularly variable stars are longer in decline than in growth of brilliancy, since such decline is no criterion of loss of heat, but rather the reverse. Why the sun and fixed stars have atmospheres largely composed of free hydrogen, and the planets have atmospheres of free oxygen and nitrogen. Why a small and sometimes even scarcely visible star occasionally is seen to suddenly blaze up, in a few hours, to hundreds of times its normal brilliancy, and then far more gradually fade, through months and years, back to its former state, in which thenceforth it continues to maintain its original lustre. Why comets, when they have tails, always project these appendages radially from the direction of the sun. How to account for the presence of cyanogen, and how for the absence of oxygen and the constant presence of hydrocarbon vapors around the nuclei of comets. Why some comets split up into separate comets and others sometimes show multiple tails. Why comets, when they pass around and behind the sun, in some cases reappear shorn of their splendor and in other cases with their splendor greatly enhanced. Whence comets are derived, where is their permanent abiding-place, and how did they originally reach those distant regions which they occupy before entering our system, if merely the dÉbris left behind from contraction of the mass of plasma out of which our solar system is supposed to have been formed. Why so many of the irresolvable nebulÆ present the appearance of divergent spirals of many different forms. How to account for the annular nebulÆ with hollow centers and for those partially-completed planetary nebulÆ, so called, which afterwards appear to retrograde into diffused gaseous nebulÆ again or gradually disappear. What is the ultimate constitution of interstellar space? Have the fixed stars planetary systems like our own, or not? Must they have such, or merely may they have? What principle of conservation of energy is it possible to apply to the vast quantities of light and heat which constantly disappear in the interstellar realms of space? How to account for this enormous emission of solar energy during the long period of time requisite for the development of the earth during its past geological ages. How to explain why the moon always presents the same face to the earth. Why, if the law of gravity prevails there, there are no visible traces of atmosphere or moisture in the moon. What is the basic principle on which depends the ratio of mean planetary distances, 0, 3, 6, 12, 24, etc., always plus 4? What is the origin of the planetary satellites and the cause of their irregular distribution, and what the origin of Saturn’s rings? How was the belt of asteroids formed between Mars and Jupiter? Why is the orbit of Neptune relatively compressed against that of Uranus? Why is the mass of Neptune out of its proper proportion compared with those of Jupiter, Saturn, Uranus, and Neptune in a diminishing series? What is the rational interpretation and what the origin of the sun’s corona and the cause of the coronal streamers?

There are many other problems equally difficult which are encountered in the study of this noble science, but the above are surely sufficiently striking. Any complete interpretation of these various phenomena, even singly, would seem to be an important step in advance; then how much more so if the explanation of one and all of these is to be found in a single, all-embracing cause, a few simple and uniformly operative principles, as unquestionably operative here as in the other fields of science to which they pertain, and which, once thoroughly comprehended and rigidly applied, will be found to elucidate all the multifarious phenomena of sidereal space so clearly and precisely that any intelligent observer and reasoner can determine each question finally for himself, and solve not only these, but all the other astronomical problems and paradoxes which have from time to time arisen? It is not to be understood that this sublime science and these illimitable realms are to be laid off with the metes and bounds of a farmer’s meadow, for all the lines of the different sciences are linked together at a thousand points, but that the operative principles which nature constantly employs once firmly grasped, the intricacy of each series of phenomena encountered will become gradually lessened, link by link, as observations and deductions are more closely and rationally made along these well-established lines of research, instead of here and there, empirically, and at hap-hazard, as has been the only method hitherto possible to pursue. When the relatively few fixed principles which control the operations of nature in the field of astronomy are thoroughly comprehended, for on this vast panorama she lays her colors with a heavy brush, we can study her phenomena and interpret her processes even more readily than the kindred sciences have enabled us to do in the adjacent fields of biology, wherein the splendid achievements of less than a quarter of a century past have not only aroused the interest and enthusiasm of the world, but already point the way to still grander triumphs yet to come.