aggregation) would be formed. Here there would be still abundance of material, but the great reduction of velocity at this distance (whether matter arriving at its journey sunwards were considered or matter voyaging away after close passage round the sun) would give a gathering mass the power to capture more matter, and so by growing rapidly to acquire fresh influence, and soon to become pre-eminent among all the subordinate aggregations.

Here, then, we should have the giant planet of the universe-not so far from the sun that the matter travelling hither and thither would be too greatly reduced, but so far away that such matter would not move too rapidly to be readily captured.

Outside this great secondary aggregation there would be aggregations smaller and smaller, owing to a reduction in the quantity of matter not compensated by the now slow reduction of the velocities. For while in the sun's neighbourhood a distance of 200 millions of miles reduces the velocity from 380 miles per second to eighteen miles per second, the velocity at Jupiter's distance is eleven miles per second, at Saturn's eight, at Uranus' six, and at Neptune's nearly five miles per second, a very much smaller proportionate reduction.

And I think that the general features of the system within the orbit of Jupiter are fairly accounted for by the theory of meteoric aggregation. For close to the sun the great velocities would enormously overbalance the great excess of material here. We should see then the least

member of the inner family nearest to the sun. There would be a gradual increase of size and importance until a maximum was attained in the case of the earth, and then as gradual a falling off towards the zone of asteroids-the region, on this view, where the influence of Jupiter on the one hand and the sun on the other would each operate to prevent the formation of a subordinate aggregation, though not preventing a cloud or flight of relatively insignificant aggregations from forming.

6

I do not enter further here into the details of this theory, because I have already considered them fully in my Other Worlds.' I must, however, note one point. It may seem at a first view that this theory of the evolution of the solar system is inconsistent with the views I have enunciated as to the formation of the larger comets by eruption from suns, and of minor comets by eruption. from the major planets. But it is not to be supposed that in the earlier stages of the history of our system matters were as they are now, and even now it may well be believed that enormous quantities of as yet ungathered materials are moving hither and thither throughout space. Growth and decay go on pari passu.

To revert to the tree which has already afforded so many illustrations of evolution theories--and illustrations so just in my opinion-we see that trees are continually throwing out matter, in leaves, buds, bloom, and fruit, which, falling eventually from the tree, is in a sense lost from its substance. This may be compared to the erup

tion or other emission of matter from the sun, and probably from the major planets of the system, as well in the present time as in long past ages. But this does not prevent us (and should not prevent a reasoning race of ephemera) from believing that the tree has grown continually even while such processes of throwing-off or loss have continued. Indeed, so constantly do we find the continuous gain of bulk which we call growth accompanied by as continuous a loss of matter, that it would be almost a fatal objection to any theory of the evolution of our system if it should fail in presenting this analogy to other known forms of growth.

But, indeed, it would be a mistake to suppose that we have gone back to the beginning of our system's history in showing how its present condition was probably evolved from a former condition. To quote words which I used two years ago in my book on the sun, 'In thus looking back at the past history of our system, we have passed after all but a step towards that primal state whence the conflict of meteoric matter arose. We are looking as into a vast abysm, and as we look we fancy we recognise strange movements, and signs as if the depths were shaping themselves into definite forms. But in truth these movements show only the vastness of the abysm, these depths speak to us of far mightier depths within which they are taking shape. Lo! these are but a portion of His ways; they utter but a whisper of His glory!'

OUR DAILY LIGHT.

God said, Let there be light, and there was light.-GENESIS i. 3.

WE are in the habit of regarding the sun as a constant source of light and heat, to which we may always trust, day after day, year after year, and century after century. And yet if we follow the only evidence which we have upon the subject-apart, of course, from that continual supply of light and heat which the sun has afforded during past ages—we might well be disposed to feel doubt on the subject. When we consider the stars, and remember that they are suns like our own, we may look to them for information as to the general laws according to which the suns which people space exist-our own included. If we find among the stars the signs of change, some stars growing fainter, others growing brighter, some fading altogether from view, and others which had been invisible becoming conspicuous objects, we should be led to doubt whether the light of our sun may not one day wane or wax in lustre, whether he may not lose so much of his brightness as no longer to supply the wants of the creatures living upon the different planets of his system,

or, on the other hand, blaze forth with so surpassing a splendour as to destroy those creatures by his excessive glory.

Now, although the stars do not teach us in this way to regard the sun's light and heat as likely to change very remarkably in the course of a moderate interval of time, yet changes sufficiently remarkable take place among them to show that we cannot place absolute reliance on the permanence of our sun's light and heat. I propose to consider a few instances of such changes.

Everyone knows the group of stars called Charles's Wain, consisting of seven conspicuous stars, three of which have been compared to the horses, while the remaining four indicate the outline of the wain or waggon. We have it on the authority of the most ancient records respecting the stars that these seven stars were once nearly equal in brightness. And in star lists made rather more than two hundred years ago we find that each of the seven was recorded as a star of the second magnitude.

We know further that Bayer, who assigning the Greek letters to the stars of a constellation followed as nearly as he could judge the order of brightness, gave to the middle star of the seven the fourth letter of the Greek alphabet, Delta. Now anyone who looks at that star group can see at once that this middle star of the set of seven is very inferior to the others in brightness. It is, in fact, now ranked as a star of the fourth magnitude, which implies, according to the best modern measurements