selves forming the centre of a remarkable group of lucid stars. This group, numbering more than 2,500 orbs, covers one half of the southern heavens. It sweeps in a mighty spiral* around the greater Magellanic Cloud. It gathers its host of lucid orbs so densely along one part of its course that that region of the heavens alone suffices to light up the southern skies as with the light of a young moon. It presents, in fine, phenomena which leave little room for question that it

The Milky way regarded as a Spiral.

forms a great and distinct system, within whose bounds are included all the characteristic features of the sidereal system itself, if indeed we are not to regard it as forming the noblest half of that portion of the universe of which we have hitherto become cognisant.

The features here referred to are very strikingly exhibited in the isographic maps of the northern and southern heavens accompanying the second edition of my Other Worlds. These maps show all the stars visible to the naked eye (in white on a black ground) truly distributed

area for area.

It is not without a purpose that I have thus directed the reader's attention to the vast southern star-system which constitutes the most striking and instructive feature of the heavens. If there is no feature of the northern heavens which to ordinary vision seems to correspond to this southern star-system, yet statistical research reveals the fact that the southern region has its true analogue in our northern heavens. The widely extended group of stars surrounding the projection of the Milky Way in Cepheus, and including within its limits the singularly rich portion of the Milky Way in Cygnus, has not only well-defined limits, but presents a well-marked superiority to the rest of the northern heavens as regards richness of star-distribution. Though smaller in extent, it is not less rich on the average than the great southern rich region. corresponds also with that region in some other and rather peculiar respects. It covers a region where the Milky Way throws out projections, and shows vast vacuities. The Milky Way reaches it on one side as a single stream, on the other as a double stream; and, further, the brightest portions of the Milky Way, in the northern and southern heavens, lie near these two rich regions, and both also towards that edge of the rich region whence the double stream of milky light extends.

It

Now, I would invite attention to the circumstance that the Sun's proper motion, according to the best estimates hitherto made, is carrying him from the borders of the southern rich region towards the borders of the northern

rich region. He is passing away from the neighbourhood of Canis Major, Columba, and Lepus (not to define too precisely the as yet scarcely determined path along which he travels), and he is urging his way with inconceivable velocity towards the region between Hercules and Lyra. Of the true habitudes of those regions of space through which he is bearing, and has lately borne, his family of planets we know little. But as we look back along the extended track he has pursued, and see the richness of those regions he has left, and as we look onwards and trace his course in imagination towards the borders of that rich region whose glories gather into their chiefest splendour in Cygnus, the conception is suggested that he is now winging his way through a relatively barren region, that he has left and will again visit more glorious stardepths than those through which he now pursues his

course.

And here we may pause for a moment to consider the nature of that path along which we ourselves are borne as the Earth sweeps on her course round the Sun.

Let the foreshortened circle in fig. 88 represent the path of the Earth about the Sun, the globe NS representing on a large scale the slope of the Earth's axis throughout her annual revolution. When the Earth is at it is mid-winter; when she is at it is spring; at it is summer; and lastly, when she is at T it is autumn. Then the path of the Sun has the position indicated in the figure, being inclined some 53 degrees to the plane of the Earth's orbit, and some 15 degrees in advance

of . Along this path the Sun pursues his course w.* at a rate which has been estimated at about 150 millions of miles, or five-sixths of the diameter of the Earth's orbit in each year. Hence, since the Earth's orbit-plane is carried along at this rate, while the Earth circles around that orbit once in each year, it follows that the actual path pursued by the Earth in

space † is such as is indicated in fig. 89. It is in fact a skew spiral or helicoidal path.‡

* Its projection on the ecliptic, that is, lies in longitude 285°, or

thereabouts.

Or rather within the sidereal system, which itself doubtless has some motion-perhaps an inconceivably rapid motion.

Some persons have expressed great anxiety lest, if the Sun is really travelling so swiftly through space, he should leave the Earth behind. There is not the least fear of this, any more than there is that the Earth should leave the Moon behind. Whatever forces have caused the Sun to follow his present career have acted upon the Earth and all the planets with equal effect. And as the Sun's course through

The other members of the planetary system pursue paths of different figures. The coils of the helicoids traversed by Mercury and Venus lie relatively close together; those of Mars are not so near as the coils of the Earth's path. The asteroidal helicoid pathsamazingly complicated they must be-are yet more drawn out (so to speak). But it is when we pass beyond the asteroidal orbits that we get the most ex

tended helicoids. Jupiter is carried some 1,700,000,000 miles onward with the advancing Sun, while he circuits once around his orbit of less than 1,000,000,000 miles in diameter; Saturn sweeps on through some 4,400,000,000 miles, while circuiting his orbit, less than 1,850,000,000 miles in diameter; and the paths

space becomes modified by the varying attractions to which he may be subjected, every planet in the solar system, every satellite, meteor, planetary comet, and asteroid, will experience the same influences, and accompany the Sun just as faithfully as at present.