The impression that the mechanics of the universe presented in the future fewer chances for discovery or advance in knowledge than in the past, could only have sprung from ignorance and underappreciation of the magnitude of the problems confronting astronomy and still to be worked out on the broader stage, not merely of the next century, but of the next millennium.

To begin, we must get down to some elementary definitions and make some sharp but fundamental distinctions as to the nature of astronomy which are ordinarily overlooked by the layman in science. All that I can do now is to show how vast is the domain which astronomy has yet to cover in its survey and how puerile is the notion that its methods have exhausted the subjects for their application, and that it has reached its term as a perfect science, or is in any respect devitalized.

First, as to definition and distinctions. Astronomy merely has to do with the positions and motions of the heavenly bodies, and its sole aim is to be able to predict these for any future time. This sums up the whole science, and we must not wander from it. The physical constitution of the past, present, or future conditions of the sun, the planets and their satellites, the stars, and the nebulas, are absolutely out of the range of its consideration. Astronomically, these are of no interest. They belong to the science of physics. Purely and simply, astronomy is the science of celestial mechanics.

Now as to its history. Its real beginning is much more recent than is ordinarily supposed. The first faint dawn of a real astronomy appears among the Arabs in the Middle Ages, but the distinct beginning of daylight in the science came at the end of the sixteenth century with Tycho and Copernicus. The former, as observer, the latter, as interpreter, by a correct system, of the apparent celestial motions, founded the science of astronomy, as Galileo had done that of astro-physics. Then came Kepler's great empirical discovery of the laws of motion in the solar system, and finally Newton placed the capstone, the law of gravitation, which crowned the structure and bound it together with principle that banished all that was arbitrary and made astronomy a deductive science. Thus with the eighteenth century the true problem of astronomy came to verify, by rigorous comparision with all the known facts of observed motion, the law of Newton as a true law of nature and to ascertain whether it was an all-sufficient explanation, or required supplementing by some other principle to account for the phenomena. Only when this was accomplished could astronomy be regarded as having advanced to the stage of a science of prediction, capable of being used confidently to trace out in advance motions and relations yet unrevealed to observation.

Astronomy is a science both of theory and observation which mutually support and control each other. It might be supposed from their interdependence that they would go hand in hand, and that their natural mode of progress would be simultaneous and equal development. The curious fact is that such contemporaneous advance is exceptional. It is true, however, that the combined efforts of mathematical and observing astronomy during the eighteenth and nineteenth centuries have brought the knowledge of our solar system, from a strictly astronomical point of view, into an extremely perfect condition. There still remain, indeed, very important problems; but it may be said, speaking in a relative way, that the astronomy of the solar system is now under control of mathematical analysis, and that we may confidently anticipate the successful explanation of some minor anomalies that yet remain. So that, if our vision were circumscribed by the solar system and the region in which its attendant comets and meteors circulate, we might look forward to a time within one or two centuries when the account would be closed and astronomy would become a perfect and, therefore, a dead science.

But the solar system is only an atom in the universe. Beyond it, at an almost immeasurable distance, lies the broad expanse of space, filled, to a limit extending beyond all powers of imagination, with an innumerable host of suns and systems. Here the astronomer has hardly begun his work, although he has not been idle. But the labor he has bestowed upon it has to a considerable extent been undertaken for an object quite secondary. He has been obliged to determine as accurately as possible the positions on the face of the sky of a very large number of stars in order to use them as reference points in determining the motions of the bodies belonging to the solar system.

During the nineteenth century a beginning was made in this great sidereal survey. The ground has been staked out, and what is in the nature of a preliminary reconnoissance undertaken. The astronomer has learned that it is highly probable that Newton's law extends to the stars and governs their motions. He infers this important proposition from the relative motions observed in a moderate number of binary stars, and feels sufficiently confident of it, at least, to pursue it as a working hypothesis in further investigation until he meets facts that contradict it, or require its modification. He has also learned by persistent and laborious measurement that a large number of the stars, at least a few thousands out of the enormous number of myriads existing, are not stationary in space. He finds reason to infer that such motions exist generally. Again he has ascertained that the sun is in motion among the stars, and the approximate direction and linear amount this motion. He has succeeded in measuring directly or absolutely the distance of, perhaps, one or two stars from our solar system; and indirectly or relatively has established a superior limit for the distances of a small number of others, perhaps a hundred in all, with more or less certainty. The smallest of these known distances is about 280,000 times the distance of the earth from the sun, but the majority are ten to twenty times greater.

This sums up fairly, I think, in a rather general way, the knowledge obtained by direct measurement. Beyond this we do not know much for certain, but by resort to assumption more or less plausible a number of interesting inferences have been drawn which may prove to be true. But the annals of astronomy are strewn with wrecks of exploded ideas based on what seemed at the time plausible grounds.

I have said enough, perhaps, to indicate the immensity of the problems which now confront astronomy and how foolish is the notion that it is in any sense a complete and perfect science. On the contrary, it has hardly put its foot over the threshold of its kingdom. It has but just begun the solution of the greater problems which must occupy the attention and labor of astronomers for many centuries. It is a labor of self-sacrifice, of sowing that others may reap. The astronomer's satisfaction in it must come from confidence that, if intelligently planned and conscientiously carried into execution, its value lies not in immediate availability but in its long-postponed, ultimate, and enduring usefulness.

From an article by Dr. Seth C. Chandler in Boston Transcript