seen four different comets. Encke, however, showed that their observations could apply only to four returns of the same revolving body, and he calculated beforehand its re-appearance in the southern part of the heavens in 1822. A material difference, however, was found to prevail between its calculated and observed places in that year, and also again in 1825 and 1828. These differences were, doubtless, partly attributable to that disturbing force from the action of the planets which, as we have already seen, they exercise upon each other. But the effect of these causes has been calculated with great care, and after due allowance for them has been made, the result has been to bring to light a 'residual phenomenon,' as Sir John Herschel expresses it, from which we arrive at the inference of a resisting medium. The effect of the obstruction arising from this fluid has been to diminish the time of the revolution of this comet by two days since the period when it was first discovered; and it is now no less than ten days in advance of the place which it would have reached, had no such resistance narrowed its orbit. It must, therefore, eventually be absorbed in the sun, however remote the period may be when that event shall take place. But we may borrow language more powerful than our

own

'The same medium,' says Mr. Whewell, which is thus shown to produce an effect upon Encke's comet must also act upon the planets, which move through the same spaces. The effect upon the planets, however, must be very much smaller than the effect upon the comet, in consequence of their greater quantity of matter.

'It is not easy to assign any probable value, or even any certain limit, to the effect of the resisting medium upon the planets. We are entirely ignorant of the comparative mass of the comets and of any of the planets;* and hence cannot make any calculation founded on such a comparison. Newton has endeavoured to show how small the resistance of the medium must be, if it exist. The result of this calculation is, that if we take the density of the medium to be that which our air will have at two hundred miles from the earth's surface, supposing the law of diminution of density to go on unaltered, and if we suppose Jupiter to move in such a medium, he would in a million years lose less than a millionth part of his velocity. If a planet revolving about the sun were to lose any portion of its velocity by the effect of resistance, it would be drawn proportionably nearer the sun, the tendency towards the centre being no longer sufficiently counteracted by that centrifugal force which arises from the body's velocity. And if the resistance were to continue to act, the body would be drawn perpetually nearer and nearer to the centre, and would describe its revolutions quicker and quicker, till at last it would reach the central body, and the system would cease to be a system.

The comparative masses of the planets, inter se, are however well known.

† Principia, b. iii. prop. x.

'This result is true, however small the velocity lost by resistance; the only difference being, that when the resistance is small, the time requisite to extinguish the whole motion will be proportionably longer. In all cases the times which come under our consideration in problems of this kind are enormous to common apprehension. Thus Encke's comet, according to the results of the observations already made, will lose in ten revolutions, or thirty-three years, less than one-thousandth of its velocity; and if this law were to continue, the velocity would not be reduced to one-half its present value in less than seven thousand revolutions, or twenty-three thousand years. If Jupiter were to lose one-millionth of his velocity in a million years, (which, as has been seen, is far more than can be considered in any way probable,) he would require seventy millions of years to lose one-thousandth of the velocity; and a period seven hundred times as long to reduce the velocity to one-half. These are periods of time which quite overwhelm the imagination; and it is not pretended that the calculations are made with any pretensions to accuracy. But at the same time it is beyond doubt that, though the intervals of time thus assigned to these changes are highly vague and uncertain, the changes themselves must sooner or later take place in consequence of the existence of the resisting medium. Since there is such a retarding force perpetually acting, however slight it be, it must in the end destroy all the celestial motions. It may be millions of millions of years before the earth's retardation may perceptibly affect the apparent motion of the sun; but still the day will come (if the same Providence which formed the system should permit it to continue so long) when this cause will entirely change the length of our year and the course of seasons, and finally stop the earth's motion round the sun altogether. The smallness of the resistance, however small we choose to suppose it, does not allow us to escape this certainty. There is a resisting medium; and, therefore, the movements of the solar system cannot go on for ever. The moment such a fluid is ascertained to exist, the eternity of the movements of the planets becomes as impossible as a perpetual motion on the earth.'-Whewell, pp. 197–200.

The inference from the discovery of the resisting medium* is, therefore, not only that Encke's comet will eventually be destroyed, but also that Mercury, Venus, the Earth, and the rest of the planets,

The zodiacal light may be seen any very clear evening soon after sunset, about the months of April and May, or at the opposite season before sunrise, as a cone or lenticular shaped light, extending from the horizon obliquely upwards, and following generally the course of the ecliptic, or rather that of the sun's equator. It is extremely faint and ill-defined, at least in this climate, though better seen in tropical regions, but cannot be mistaken for any atmospheric meteor, or aurora borealis. It is manifestly in the nature of a thin lenticularly-formed atmosphere, surrounding the sun, and extending at least beyond the orbit of Mercury, and even of Venus, and may be conjectured to be no other than the denser part of that medium, which, as we have reason to believe, resists the motion of comets; loaded, perhaps, with the actual materials of the tails of millions of those bodies, of which they have been stripped in their successive perihelion passages, and which may be slowly subsiding into the sun.'-Sir J. Herschel's Treatise on Astronomy, pp. 407-8. c 2

must

must be successively precipitated on the Sun, and effaced from the universe. It is of no consequence whatever to the truth of the argument, that these are events which require for the natural period of their accomplishment millions of years, a period of which we can form no conception. Nor is it necessary that we should. Our faculties are suited to the purposes of a short existence on a particular planet. The higher intelligences must look upon us as mere ephemera or rather the beings of a moment. Can we count the objects which the microscope discloses to our view? Have we yet, after the observations of nearly four thousand years, been able to number the stars? How then shall we calculate the years still remaining to be accomplished by the solar system? But the difficulty which we have in doing this, or rather its impossibility, has no effect upon the discovery, which shows that however remote the day, yet a day is undoubtedly assigned when the solar system shall cease to be. The consequence admits of no question. That system which is destined to decay cannot be eternal. As it is to have an end, it must have had a beginning. The time was when it did not exist. The time is yet to come when it will exist no more. It must then have been of necessity created by some Power, which is competent to such a prodigious work-a power unlimited in its attributes, and thus we return once more by unerring steps to the existence of an Omnipotent Creator, to whose view our millions of years calculated by revolutions round the sun are but the results of a law which is unknown in eternity.

We are in the habit sometimes of contrasting the transient destiny of man with the permanence of the forests, the mountains, the ocean, -with the unwearied circuit of the sun. But this contrast is a delusion of our own imagination; the difference is after all but one of degree. The forest tree endures for its centuries and then decays; the mountains crumble and change, and perhaps subside in some convulsion of nature; the sea retires and the shore ceases to resound with the everlasting voice of the ocean; such reflections have already crowded upon the mind of the geologist, and it now appears that the courses of the heavens themselves are not exempt from the universal law of decay; that not only the rocks and the mountains, but the sun and the moon, have the sentence" to end" stamped upon their foreheads; that they enjoy no privileges beyond man, except a longer respite. The ephemeron perishes in an hour; man endures for his three score years and ten; an empire or a nation numbers its centuries, it may be its thousands of years; the continents and islands which its dominion includes have perhaps their date, as those which preceded them have had; and the very revolutions of the sky by which centuries are numbered, will at last languish and stand still.'-Whewell, pp. 202, 203. These reflections lead us to the conclusion, that the district of

which we are a part, has still a multitude of centuries to count, before, in the ordinary course of things, it shall be destroyed. Even with respect to Mercury, the effect of the resisting medium has as yet produced no changes that we can discover. That its influence is therefore very minute, even in thousands of years, we may feel assured; and we also may believe, that as the Creator operates by his own laws, he will permit them to take their course, and accomplish their object without interruption. Our globe must, consequently, be still in the very swaddling clothes of its birth, and man, as to experience, a mere infant. We cannot guess at the susceptibility for further and higher improvements in the sciences and arts, in civilization, and above all, in religion, which may be imparted to him by the new stages of existence that are still to arrive. We cannot look forward to the lapse of even one hundred thousand years, without supposing that, in that time at least, education and Christianity would be universal over the earth. The generations of those distant times would look back upon ours as a period of comparative obscurity and barbarity. War would be unknown to them. All the necessary points of legislation and economy would have been fully arranged. Communications between all nations would have been facilitated in every way that ingenuity could devise. New empires would have arisen, and perhaps new continents have emerged from the bosom of the deep; and reason and knowledge would be found, as uniformly as they ought to be, the friends and not the enemies of faith.

There is, indeed, hardly a circumstance connected with our existence, which, when examined with a little attention, does not yield abundant evidence of the wisdom and beneficence which preside over the universe. We have only to turn up the soil at our feet, to find in it innumerable seeds useful to man.* We have only to look around us upon the surface of the earth, to see it stocked with a variety of animals, conducive not only to our subsistence, but to our convenience and recreation. The sea also, and the air, have their population at our command; and the more deeply we investigate the laws by which the whole system of vegetable and animal life is governed, the more clearly we shall perceive their complete and exclusive adaptation to the planet on which they carry on their operations.

* ' So completely is the ground impregnated with seeds, that if earth is brought to the surface, from the lowest depth at which it is found, some vegetable matter will spring from it. In boring for water lately, at a spot near Kingston-on-Thames, some earth was brought up from a depth of three hundred and sixty feet: this earth was carefully covered over with a hand-glass, to prevent the possibility of other seeds being deposited upon it, yet in a short time plants vegetated from it.'-Jesse's Gleanings in Natural History, pp. 139, 40.

Thus

Thus we find in the internal functions of plants, a complete cycle, which corresponds exactly with our year. Most of our fruit trees, for example, require the spring for the ascent of the sap, the summer and autumn for ripening the fruit, and the winter for hardening the wood which the tree has made during the previous season. Suppose the Earth to be placed where Venus is: its year would then consist of only seven months, a change which would throw the whole of our botanical world into confusion. The tree, after having put forth its leaves, blossoms, and fruit, would be destroyed at once by a winter which would come instead of autumn. Suppose the Earth to be removed to the orbit of Mars its year would then consist of twenty-three months. Six months of continued spring or of summer may very well suit vegetable life in Mars, but to that of Earth, either would be destructive. If the wheat ear were to remain exposed to the sun of a six months' summer, the grain would be reduced to chaff. If it were green during a spring of similar length, it would never come to maturity. Either our vegetables are suited to our year, or our year to them. In either case we see a law of mutual adaptation, which demonstrates the necessity of previous design.

A similar observation applies to the length of our day. There are numerous flowers, such as the day lily, the common dandelion the hawkweed, the marigold, and others, which open and close at certain hours, as anybody who attends to the floral world must have observed. If the day were considerably lengthened or shortened, the clockwork of these productions, if we may use the expression, would require a totally new construction, in order to adjust their hours to the changes in the rising or setting of the sun. Night is for man and almost all animals the period of repose. If the day and night were lengthened to forty-eight hours, his present strength would not enable him to toil for twenty-four hours, even with the intermissions to which he is now accustomed, and it would be impossible for him to sleep more than eight or ten hours at the utmost. The remaining fourteen hours of night would be wholly lost, for he could not turn them to advantage either by mental or bodily occupation. Here is another manifest proof of design, whether we consider the present habits of animal life to be suited to the period of the earth's revolution round its own axis, or that revolution to them.

The force of gravity within the region immediately influenced by the earth depends upon the mass of the earth-and this mass is, as we have seen, one of the elements of the solar system. Our globe might have been as large as Jupiter or Saturn, or as small as Pallas or Ceres, without causing any derangement, apparently, in the general system to which it belongs. But if the earth were

as