In the preceding chapters we have dealt with the gigantic bodies which form the chief objects in what we know as the solar system. We have studied mighty planets measuring thousands of miles in diameter, and we have followed the movements of comets, whose dimensions are to be told by millions of miles. Once, indeed, in a previous chapter, we have made a descent to objects much lower in the scale of magnitude, and we have examined that numerous class of small bodies which we call the minor planets. It is now, however, our duty to make a still further, and this time a very long step, downwards in the scale of magnitude. Even the minor planets must be regarded as colossal objects, when compared with those little bodies whose presence is revealed to us in a most interesting, and sometimes in a most striking manner.

These small bodies compensate in some degree for their minute size, by the enormous profusion in which they exist. No attempt, indeed, could be made to tell in figures the myriads in which they swarm throughout space. They are probably of very varied dimensions, some of them∧ being many pounds or perhaps tons in weight, while others seem to be not larger than pebbles, or even than grains of sand. Yet, insignificant as these bodies may seem, the great sun himself does not disdain to accept their control. Each particle, whether it be as small as the mote in a sunbeam or as mighty as the planet Jupiter, will perform its path around the sun in conformity with the laws of Kepler.

Comparing the methods now available for astronomical inquiries with those in use thirty years ago, we are at once struck with the fact that they have multiplied. The telescope has been supplemented by the spectroscope and the photographic camera. Now this really involves a whole world of change. It means that astronomy has left the place where she dwelt apart in rapt union with mathematics, indifferent to all things on earth save only to those mechanical improvements which should aid her to penetrate further into the heavens, and has descended into the forum of human knowledge, at once a suppliant and a patron, alternately invoking help from, and promising it to each of the sciences, and patiently waiting upon the advance of all. The science of the heavenly bodies has, in a word, become a branch of terrestrial physics, or rather a higher kind of integration of all their results. It has, however, this leading peculiarity, that the materials for the whole of its inquiries are telescopically furnished. They are such as the unarmed eye takes no, or a very imperfect cognisance of.

Spectroscopic and photographic apparatus are simply additions to the telescope. They do not supersede, or render it of less importance. On the contrary, the efficacy of their action depends primarily upon the optical qualities of the instrument they are attached to. Hence the development, to their fullest extent, of the powers of the telescope is of vital moment to the progress of modern physical astronomy, while the older mathematical astronomy could afford to remain comparatively indifferent to it.

We have now to consider labours of a totally different character from those of Sir William Herschel. Exploration and discovery do not constitute the whole business of astronomy; the less adventurous, though not less arduous, task of gaining a more and more complete mastery over the problems immemorially presented to her, may, on the contrary, be said to form her primary duty. A knowledge of the movements of the heavenly bodies has, from the earliest times, been demanded by the urgent needs of mankind; and science finds prosperity, as in many cases it has taken its origin, in condescension to practical claims. Indeed, to bring such knowledge as near as possible to absolute precision has been defined by no mean authority as the true end of astronomy.

Several causes concurred about the beginning of the present century to give a fresh and powerful impulse to investigations having this end in view. The rapid progress of theory almost compelled a corresponding advance in observation; instrumental improvements rendered such an advance possible; Herschel's discoveries quickened public interest in celestial inquiries; royal, imperial, and grand-ducal patronage widened the scope of individual effort. The heart of the new movement was in Germany. Hitherto the observatory of Flamsteed and Bradley had been the acknowledged centre of practical astronomy; Greenwich observations were the standard of reference all over Europe; and the art of observing prospered in direct proportion to the fidelity with which Greenwich methods were imitated.

The progress of astronomy during the last hundred years has been rapid and extraordinary. In its distinctive features, moreover, the nature of that progress has been such as to lend itself with facility to untechnical treatment. To this circumstance the present volume owes its origin. It embodies an attempt to enable the ordinary reader to follow, with intelligent interest, the course of modern astronomical inquiries, and to realise (so far as it can at present be realised) the full effect of the comprehensive change in the whole aspect, purposes, and methods of celestial science introduced by the momentous discovery of spectrum analysis.

Since Professor Grant's invaluable work on the History of Physical Astronomy was published, a third of a century has elapsed. During the interval, a so-called “new astronomy” has grown up by the side of the old. One effect of its advent has been to render the science of the heavenly bodies more popular, both in its needs and in its nature, than formerly. More popular in its needs, since its progress now primarily depends upon the interest in, and consequent efforts towards its advancement of the general public; more popular in its nature, because the kind of knowledge it now chiefly tends to accumulate is more easily intelligible–less remote from ordinary experience–than that evolved by the aid of the calculus from materials collected by the use of the transit-instrument and chronograph.

Johann Hieronymus SchrÖter was the Herschel of Germany. He did not, it is true, possess the more brilliant gifts of his rival. Herschel's piercing discernment, comprehensive intelligence, and inventive splendour were wanting to him. He was, nevertheless, the founder of descriptive astronomy in Germany, as Herschel was in England.

Born at Erfurt in 1745, he prosecuted legal studies at Göttingen, and there imbibed from Kästner a life-long devotion to science. From the law, however, he got the means of living, and, what was to the full as precious to him, the means of observing. Entering the sphere of Hanoverian officialism in 1788, he settled a few years later at Lilienthal near Bremen, as “Oberamtmann,” or chief magistrate. Here he built a small observatory, enriched in 1785 with a seven-foot reflector by Herschel, then one of the most powerful instruments to be found anywhere out of England. It was soon surpassed, through his exertions, by the first-fruits of native industry in that branch. Schrader of Kiel transferred his workshops to Lilienthal in 1792, and constructed there, under the superintendence and at the cost of the astronomical Oberamtmann, a thirteen-foot reflector, declared by Lalande to be the finest telescope in existence, and one twenty-seven feet in focal length, probably as inferior to its predecessor in real efficiency as it was superior in size.