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we were for the first time introduced to this glorious earth with its balmy atmosphere-its pure and translucent waters-the life and beauty of its animal and vegetable kingdoms-with its attraction upon the matter of our own bodies just sufficiently great to give them the requisite stability, and yet not so great as to deprive them of the power of free and rapid motion-with its intervals of light and darkness, giving an alternation of labor and rest nicely corresponding with our muscular power-with its grateful succession of seasons, and its moderate extremes of temperature, so justly suited to our organization: with all this fitness before us, could we hesitate to infer that such a place must have been provided expressly for our habitation? If, then, the discoveries of modern science disclose to us in each planet, which, like our own, rolls in regulated periods round the sun, provisions in all respects similar-if they are proved to be habitations similarly built, ventilated, warmed, illuminated, and furnishedsupplied with the same alternations of light and darkness by the same expedient-with the same pleasant succession of seasons-the same geographical diversity of climates-the same agreeable distribution of land and water-can we doubt that such structures have been provided as the abodes of beings in all respects resembling ourselves? The strong presumption raised by such proofs is converted into a moral certainty, when it is shown from physical analogies of irresistible force that such bodies are the creation of the same Hand that raised the round world and launched it into space. Such, then, is the nature of the evidence which science offers on this interesting question. Let us endeavor to strip it of such technical forms of language and reasoning as are intelligible only to the scientific, and to present it so as to be easily and agreeably comprehended.

If we look at a plan of the solar system, the first glance will impress us with an idea that the earth is an individual of a class; that that class is the planets; that the sun is an object provided for different purposes, and the same may be said of the satellites. We take this impression from the simple fact that the planets, including the earth among the number, move round the sun as a centre in circles all in the same direction, and nearly in the same plane; while the satellites or moons (in a manner which we shall hereafter notice) revolve respectively round the planets. The impression is irresistible that the planets, including the earth, form a class; but let us see the purposes in the economy of nature which are fulfilled by this common character given to the motion of the planets and the position of the sun. We find, upon considering the qualities of organized bodies, and especially the species of the animals and vegetables upon the earth, that the maintenance of their physical well-being is essentially dependant on the uniformity and regularity with which they are supplied with the two great physical principles of light and heat. Should these, or either of them, be subject to any extreme variations, such vicissitudes would be incompatible with the organization of the species. There is a cold on one hand and a heat on the other, under which no organized body could continue to exist, and there are still narrower limits within which it is necessary to confine the temperatures they are exposed to in order to secure the perfection of their physical health. There are also degrees of light, the intensity of which would be incompatible with the continued perfection of the organs of vision.

We see, then, how essential to the well-being of the infinite varieties of creatures that people this globe, a uniform regulation of light and heat is. How, then, is this great and important end attained? If we had a fire which at once supplied light and heat in our neighborhood, and that circumstances obliged us continually to shift our position in regard to it, but at the same time so to order our movements as to receive from it a uniform intensity of light and heat, how

should we move? Should we not take care to keep always at the same distance from it? And to accomplish this, should we move in any other path than that of a circle, having the fire in the centre? This, however, is precisely what is accomplished by the annual motion of the earth. It traverses its course round the central fire of the system, keeping always nearly at the same distance from the inexhaustible fountain of light and warmth. By this simple expedient of observing a circular path, with the sun in the centre, this necessary object is attained.

Now, in examining the movements of all the other planets, we find that the same expedient is provided: that they severally, in their periodical courses, like the earth, preserve uniform distances from the sun-moving round that body in circles, of which it is the common centre.

Seeing, then, that this motion in the case of the earth is a means whereby an important end is attained, analogy justifies the conclusion that it is to be regarded likewise as a means for the attainment of a similar end in each of the planets. But it will probably be said that the planets are at different distances from the sun; that the most remote of them is nearly twenty times farther from that luminary than the earth, while the nearest of them is little more than one third the earth's distance; therefore, that although it must be admitted that each planet (considered per se) is supplied uniformly with light and warmth by this circular motion; yet the intensity of these principles to which the several planets are exposed, comparing one with another, is so extremely different ast to destroy all analogy between them.

In answer to this, we are, however, to consider that the influence of light and The heat upon a planet does not depend solely on its distance from the sun. heat, as is well known, produced by the solar rays, depends on the density of the air which surrounds the objects affected by it. Thus we find the temperature, at great elevations in our own atmosphere, considerably lower than at the mean surface of our globe; because at these elevations the air becomes so thin as to be incapable of collecting and retaining the sun's heat. We can therefore easily imagine, provided the existence of their atmospheres be conceded, that their density has been so regulated, that the nearest planets to the sun, which receive the greatest intensity of its rays, may not, after all, be more heated than the most remote ones, which are exposed to the least intensity of its rays just as we find that the temperature of the summits of lofty mountains at the tropics is as low as the temperature of some of the polar latitudes. It is plain, then, how the effects of the various distances of the planet from the sun may be equalized and compensated. The means of accomplishing this are provided in the form of atmospheres, as we shall presently see.

But let us turn to the consideration of the solar light. The intensity of the sun's light varies with his distance exactly in the same proportion as that of his heat; and the brightness of a day in the most remote planet would be less than that of a day in the nearest in the same proportion as the sun's heat would be less. It may therefore be objected that there might be scarcely daylight enough in the planet Herschel to serve the purposes of social and civil life. Such might undoubtedly be the case if we were to deny the possibility of any variation, however minute, in the organs of vision; but without denying this, let us consider how the matter would stand. The perception which the eye of any creature acquires of light, depends (cæteris paribus) upon the magnitude. of the circular aperture or foramen, in front of the eye, called the pupil, which has, externally, the appearance of a circular black spot; but which is, in reality, a circular hole through which the light is admitted to the interior of the chamber of vision, there to affect the membranous coating which transmits its influence to the brain and causes the sensation. It must be evident, even to

the least informed, that the brightness of light will then depend upon the magnitude of this foramen. Granting that there are two eyes, in one of which the pupil is twice as large as it is in the other, the organ being in all other respects the same, then it is evident that one would admit twice as much light as the other. If, then, the large pupil was exposed to light of only one half the intensity or brightness of that to which the smaller one is exposed, then the two lights would appear to these eyes of the same brilliancy, although in fact, one would be only half as bright as the other. What, then, shall we say of the planets? Grant that the pupils of the eyes of all creatures endowed with vision upon them are enlarged in their opening according as the planets are more removed from the sun and diminished as they are nearer to that luminary, and the whole difficulty arising from the varying intensity of light will vanish. The inhabitants of all the planets will, in fact, enjoy days of the same brightness, notwithstanding the extreme difference of their distances from the sun. In considering closely the physical powers of locomotion and strength conferred upon animals on the surface of the earth, we find that they have certain limitations; that animals are capable of exercising the powers of locomotion for certain periods of time, varying, it is true, among individuals, but still in the main comprised within certain narrow limits. We find that after the lapse of certain intervals, bodily repose is wanted. But besides the disposition to activity and locomotion and the alternate want of rest, animals in general have also other physical wants and capabilities of enjoyment which are periodical. Thus they are capable of wakefulness for certain periods, after which recurs the physical want of sleep.

Now upon a general survey of the creation, it is found that the average periods which must regulate the intervals of labor and rest, of wakefulness and sleep, corresponds in the main with those which regulate the alternations of light and darkness. In the vegetable kingdom we find prevailing also periodical functions, certainly not so obvious and apparent, but not on that account the less interesting, which are ascertained to have the same close alliance with the period that regulates the returns of light and darkness.

Plants undergo certain changes and suffer certain effects, in the presence of solar light, which are different from, and in some respects contrary to, those which they undergo in its absence. These changes are essential to the vegetable health of the creature; without them the tribes of plants would be extinct. The duration of these operations is just as essential as their alternations. Light must be present a certain time and neither more nor less; and its absence must be equally regulated by limits, otherwise the plant must perish. There is, then, it is evident, an essential relation between the functions and qualities of the vegetable kingdom-between the power of activity, the susceptibility of enjoyment and the physical wants of animals, and the periods which separate light from darkness; but what are those periods? What is the mechanical expedient to which He has resorted to accomplish his inscrutable purposes, who divided the light from the darkness, and "saw that it was good." Nothing can be more simple. Nothing can be more beautiful. Nothing can be more admirably perfect. While the globe of the earth makes its annual course round the sun, it has at the same time a spinning motion, on a certain diameter, as an axis, in virtue of which it successively exposes all parts of its surface to the light and warmth of the sun. Each complete rotation is accomplished in the space which we call twenty-four hours; subject to a variation which we shall notice hereafter. All points on our earth are alternately exposed to and withdrawn from the solar light; the average intervals being twelve hours.

Now when we reflect on the close, the exact correspondence between these

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intervals and the indispensable wants of all organized creatures, can we for a moment doubt that the earth was made to turn upon its axis in that particular time rather than any other, because it was more conducive than otherwise to the well being of the countless myriads of species, the production of the Divine hand, for whose enjoyment the earth was made? Had the time of rotation been materially less than it is, our periods of activity and labor would be too short to prepare us for the return of darkness, and had the time of rotation been greater, we should have needed rest before the return of the natural epoch designed for it. As it is, the natural vicissitudes are nicely adapted to our wants; and yet our organization is in no way connected physically with the rotation of the earth, by any relation of the nature of cause and effect, and to suppose such an adaptation fortuitous, would be an outrage upon all principles of probability. This mutual fitness is, then, another of the many proofs which offer themselves that the earth as a dwelling, and man as a dweller, has been each expressly designed for the other.

Many practical examples may be given of this correspondence between the time of rotation of the earth upon its axis and the periodical functions of the organized world. Thus, Linnæus proposed the use of what he termed a floral clock, which was to consist of plants which opened and closed their blossoms at particular hours of the day. Thus, the day-lily opens at five in the morning, the common dandelion at six, the hawkweed at seven, the marigold at nine, and so on; the closing of the blossoms marking corresponding hours in the afternoon. Nor was this to be regarded as a specific effect of light upon the plants, for when the flowers were introduced into a dark chamber they were found to open and close their blossoms at the same times.

The necessity of observing a correspondence between the intervals of activity and repose, the taking of food, &c., and the period of light and darkness, was practically shown in the case of voyages made to the north pole, where navigators attained those latitudes in which the sun never rises for several weeks, in which cases it was found necessary to make the crews of the ships adhere with the utmost punctuality to the habit of retiring at nine o'clock and rising at a quarter before six. Under these circumstances they enjoyed a state of salubrity very remarkable, notwithstanding the trying severity of climate to which they were exposed.

Seeing then, that the expedient of making the globe of the earth turn upon its axis in twenty-four hours is one productive of such multifarious benefits, and so intimately related to the organized species of our globe, that were it to turn otherwise than it does, in a greater or less time, an entire derangement of the animal or vegetable economy would ensue,-it becomes an interesting question to ascertain whether the other planets are provided with a similar expedient; and if so, to what extent the application of such expedient corresponds with the case of the earth. We accordingly find that all the planets without exception have a motion of rotation on certain diameters as an axis while they make their periodical revolutions round the sun, and that the diameter in which they so rotate has been selected in such a manner as to secure to each of them regular alternations of light and darkness in every part of their surfaces; in fact, they, like the earth, have days and nights. But are those days and nights regulated by the same intervals as ours? for that is an important question; such intervals being, as we have shown, a key to the organizations and functions of the creatures upon them respectively.

We shall on another occasion show that the planets consist of two groups which, although characterized by common qualities, are still distinct in several particulars. The inner group consists of Mercury, Venus, Mars, and the Earth; the outer group consists of Jupiter, Saturn, and Herschel. There are circum

stances which prepare us to expect some discrepancies in the provisions made in these two groups; but everything leads us to anticipate a uniformity in each of them respectively. We shall on another occasion show that the three planets, Mercury, Venus, and Mars, which with our own form the inner group, do all turn on their axes; that they have all a diurnal motion completed in the same time, or very nearly so, as that of the earth. Thus these several planets not only have days and nights, but have days and nights precisely similar to our own. They are regulated by the same average duration; and He that gave them those alternations has seen it good to "divide the light from the darkness" after the same fashion.

If, then, the duration of our days and nights be evidently regulated with a view to the accommodation and well-being of the organized creatures to which the earth has been appropriated, we are surely warranted by all analogy in concluding that the adaptation of the same expedients in the planets, Mercury, Venus, and Mars, have been directed to the same beneficent purposes, and that the creatures upon them, as upon the earth, are so organized as to require the same intervals of labor and rest, of activity and repose, of wakefulness and sleep.

In the outer group the times of rotation are different, yet among them a similar uniformity prevails. Jupiter and Saturn revolve on their axes in about ten hours. The telescope has not informed us of the time of rotation of Herschel; but it is probably not different from the two cognate planets. It appears then that the intervals of light and darkness in these remote bodies, instead of being regulated by intervals of twelve hours, is determined by average intervals of five hours. A corresponding difference of organization and functions may of course be inferred to prevail upon them; but still it will be observed that the difference between them and the inner group, lies merely in the duration of intervals of light and darkness; those intervals being in the main preserved. There is no planet, then, in which are not provided days and nights.

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In considering the expedient by which days and nights are secured to the planets, it is interesting to contemplate the particular position of the diameters on which they have been made to turn. There are a great variety of different diameters upon which the earth might have spun while it revolves round the It might, for example, have turned on a diameter at right angles to its annual orbit. If it had been so we should have had equal days and nights throughout the entire year, and at every part of the earth. It might again have turned upon a diameter lying in the plane of its annual orbit. In such a case we should not have had alternations of days and nights at all; we should have had the sun constantly visible for six months, and absent for other six months, modified in a very complex manner, however, by other vicissitudes; in fact we should have had changes of light and darkness utterly unfit for our wants. In the first case we should have been deprived of seasons and of the means of maintaining any convenient chronology. Thus, in either case, we should be stripped of many of the benefits and utilities arising from the present arrangement. Again, the earth might have turned upon an axis nearly perpendicular to the plane of its annual orbit; or in nearly that plane; it might, in fact, be inclined in any position, between those extremes. Had it stooped down nearly to the ecliptic, consequences would have ensued almost as fatal as those which any position in the plane of the ecliptic would have inferred. We find, however, in fact, that a position has been given to this axis slightly inclined from the perpendicular. In virtue of this inclination the northern hemisphere leans toward the sun during one half of the year, and the southern hemisphere during the other. We enjoy the grateful succession of seasons; it is thus that spring, summer, autumn, and winter, follow each other with pleasant variety, marking in their

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