rate of more than twenty miles per second. Since he made this discovery a telescope better suited for the work has been placed in his hands by the Royal Society, and with this he has recognised motions of recession or approach in the other bright stars, some of these motions taking place at the rate of more than fifty miles per second.

In another chapter I shall describe certain peculiarities which characterise the stellar motions, and in particular (1) the evidence which the star motions afford as to the motion of our own bright particular star,' the sun, with his scheme of dependent worlds, and (2) the evidence of certain drifting motions among particular star groups.

THE DRIFTING STARS.

IN former chapters I have compared man to the May-fly, and his sonceptions of the universe, or what he calls the universe, to the ideas which a reasoning May-fly might form of the objects amidst which his brief career is passed. And surely there is no subject of research which suggests such a comparison more forcibly than the study of star movements. A child is born into the world, grows to manhood, becomes, perchance, what we call great, lives to the threescore years and ten, or even to those fourscore years which bring with them weariness of life; and during all those years the great universe of stars which encompasses us on every hand remains to ordinary perceptions unchanged. Let the heavens be studied on the first night after that man was born, and let them again be studied on the first night after his death, and no change in the distribution of the stars shall be perceived.

And yet during all the years which have elapsed every one of those orbs which seem so steadfast has been rushing onwards at a rate compared with which the swiftest forms of motion with which we are acquainted—

the speed of the express train, the flight of the bird, even the rush of the missiles which we poor ephemera employ to destroy our fellow-creatures—are as absolute rest. In every second yon busy star which seems so still has urged its way thirty or forty miles upon its wide and as yet undetermined career. Not for a moment does it rest, even when unseen by human eyes; and yet the career of the most long-lived of our race passes while that star remains to all ordinary perceptions in an unchanging position.

Yet our short-lived race, puny and feeble though it appears compared with the wondrous orbs amidst which the earth on which we live exists, has deliberately undertaken and not unsuccessfully carried out, the daring scheme of determining according to what laws the stars move, and in particular (for in reality this scheme is the most daring of all) of ascertaining from the seeming motions of the stars how the sun, that vast orb of which our earth is a minute dependent upon whose surface man is a most minute moving creature, is moving through star-bestrewn space.

We owe to Sir W. Herschel the first conception of the method by which the star motions were to be analysed for the detection of the motion of our own sun. It is clear that if all the stars were at rest, and our sun were moving in their midst, then the other stars would appear to be affected by motions corresponding to the real motions of the sun. If the sun were travelling on a great

level plain, upon which lay all the other stars, we might say that the stars to right and left of him would appear to be moving backwards, precisely as the trees, houses, and other objects at rest on either side of the track of a moving carriage seem to be travelling backwards. But as the stars do not lie on a plane surface, but are scattered throughout the length and breadth and depth of space, we cannot so describe their apparent motions. Nevertheless it is clear that stars on all sides of the sun must appear to travel backwards if he is travelling in any direction forwards.

It is common to find it stated that the stars of the region towards which the sun is travelling would appear to open out, just as the trees of a forest seem to open out from each other as the traveller advances towards them; and that the stars of the region which the sun is leaving would seem to draw closer together. But no such effect could be expected to be recognisable, because the distances of the stars are so great. Precisely as when we are travelling in a carriage the objects on either side are those chiefly affected by apparent motion, so with the stars: those on every side of the course of the advancing sun would be more affected than those lying in regions towards which, or from which, he is moving.

But a difficulty is introduced in the case of the sun which does not appear in the case of some traveller moving onwards amidst a number of objects at rest. We only infer that the sun is moving because we have seen

that the stars are moving. And we cannot for a moment suppose that all the star motions are merely apparent, and due in reality to the sun's motion. For why should the sun, which is only one among many hundreds of thousands of suns, be the only one which is moving? Apart from this, the motions of the stars are altogether too diverse in character to be ascribed to any such simple cause as the motion of the sun alone, even if that were in itself a reasonable or likely supposition. So that the astronomer who wishes to learn in what direction the sun is moving has not the same sort of evidence to guide him which is afforded to one travelling amidst a number of objects at rest. The sun is surrounded by a multitude of moving objects, and, to make the determination of his motion infinitely more difficult, those objects lie at unknown distances, are moving in unknown directions, and have unknown velocities.

Very wonderful is it, therefore, that Sir W. Herschel first, and afterwards several other astronomers have, by the careful study of the stars' movements, ascertained, with what amounts practically to absolute certainty, that our sun, with his whole family of planets, is moving towards the part of the heavens occupied by the constellation Hercules. Every investigation of the evidence has led to the same general result in this respect. But as to the rate of the sun's motion, which is not uncommonly presented as though it rested on the same footing, the evidence is very much less convincing. It has been said.