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My object on this occasion is, in itself, a very simple one. I desire to give some illustrations of the vastness of the visible creation, as made known by modern astronomy. I say emphatically modern astronomy, for some knowledge of this science is probably nearly as old as the world itself. Almost from the first issuing of the great decree that the sun and moon should serve for signs, and for seasons, and for days, and for years, men have been careful to observe the heavens ; for the Great Creator had so written that decree upon the heavens themselves that men have not been slow to read the lesson thus visibly inculcated. I would observe, moreover, that the objects of astronomical research, with very trifling exceptions, are, of all others, with which we have to do, the most unalterable. It is almost exactly true that the very constellations which we now see were gazed upon by the antedeluvian patriarchs; were in full view of Noah when the great flood of waters was upon the earth; met the upturned eye of Abraham when he was led out by Divine command to behold in them the symbol of the promise; guided the ancient Greeks in navigation, and still serve the modern astronomer as so many guide-points in the heavens.

My purpose, as already indicated, is to illustrate, not to demonstrate. To accomplish the latter in a single lecture would not be practicable ; and certainly of astronomy, above all other sciences, it is true that it may throw itself on its character for veracity when it requests that its conclusions should be received as reliable. A science which can trace a comet in its course, where no eye has had even a telescopic view of it for three-quarters of a century, and bring it back by computation correctly almost to a day, or which can predict an eclipse a century hence as readily as one that will occur this year, and to whose accuracy experience throughout bears such abundant testimony—such a science may fearlessly throw itself on its character for veracity. Before I proceed, however, to elucidate the subject, let me call attention for a moment to an old-fashioned problem, whose bearings upon the subject will, I trust, be presently seen. I allude to the problem of the price of a horse, in which a farthing was allowed for the first nail in his shoes, two for the second, four for the third, and so on. There were thirty-two nails in all, and yet, from the small beginning of a farthing, owing to this doubling thirty-one times, the value of the horse was only to be computed in millions of pounds. Now, with reference to the subject of astronomy, we shall have occasion to see that, though commencing with a comparatively moderate unit, we shall advance upon a similar plan, but much more rapidly. Keeping, then, in view the illustration already given, you will at once see how gigantic, after a very few steps, must

be the last result compared with the first. Our first object to-night will be to gain some idea of the size of the earth itself, on which we stand. The half diameter of the earth is the

measuring unit with which to compare the distance of the earth from the sun, and thus obtain a new unit with which afterwards to compare the distances of the other planets. To give a just idea of the size of the earth we will avail ourselves of the largest tangible measure attainable, that is, the highest mountain on the earth's surface. The highest mountains are the Himalayas, their altitude being five and a half miles. Now, we do not exaggerate when we say that, if we could uncover the base of one of those mountains, it would cover four times the original area of the District of Columbia, or the surface of one of the ordinary counties of our States, rising above that surface to the height of five and a half miles, about equal to the height of Chimborazo added to that of the highest of the Alps. This shall be our standard of comparison with regard to the magnitude of the earth. Such a mountain is rather more than 14to of the earth's diameter or about 727 of its radius. In making the comparison, after the ordinary mode, two difficulties present themselves. It is said that, if you represent the earth by a globe, the highest mountain on its surface may be represented by a small grain of sand. You thus proceed from the greater to the less, whereas, in nature, we must proceed from the less to the greater. Besides, a grain of sand is too small to give an adequate idea of the matter to be illustrated. To avoid this we shall make use of a scale sufficiently large to present the mountain distinctly, and shall proceed in the natural order from the less to the greater. This diagram before me is thirty-nine feet six inches in length, and is intended to represent two radii of the earth opening to the extent of one degree. At the further end of it is a blue band, representing the atmosphere, and immediately beneath which is a small row of mountains. Their heights, on this scale, is a trifle less than two-thirds of an inch, and their actual height, as compared with the real half diameter of the earth, is as two-thirds of an inch compared with thirty-nine and a half feet, and doubling the half diameter we shall have the ratio of two-thirds of an inch to seventy-nine feet. Below the row of mountains you have a dark blue band, representing the ocean.

Below that again a darker portion still, representing that portion of the earth's crust through which you must go to find a red heat, and beyond that you have the red color continued until it passes into whiteness; it indicates the depth at which we would probably arrive at a white heat.

[It would be impossible, in a wood-cut, to do justice to the illustration here explained by the lecturer. The explanation itself will doubtless be sufficient.]

The diameter of the earth is, then, a very large unit in comparison with the height of the highest mountain. The circumference, of course, is more than three times the diameter. If you should attempt to walk around the earth at the rate of twenty miles a day, three years and five months would be spent in completing the circuit; and if you should fly around it at the rate at which the steam car travels, say thirty miles an hour, you would accomplish its circuit in thirty-four and a half days; but, if its circumference be great in comparison with ordinary standards, its surface in comparison with that of a sphere of ordinary size must be still more enormous. The illustrations, I would

remark, that I give you here, are most of them originally devised, and the results in all cases verified by actual computation. We could not pass over the surface of the earth and take a good look at the surface at a more rapid rate than that of twenty square miles a day, and yet this would occupy us a period of 27,000 years. To view that portion of the earth which is inhabited, if we should estimate it at but onefourth of the whole, would, at the same rate of progress, require 6,750 years; or to view the habitable portion of the surface of the earth would require, in the case of the same individual, provided he could live so long, more than the time from the creation of man down to the present day to walk. If the surface of the earth be so large, its capacity, of course, compared with an ordinary standard, will be found to be to it in a still greater ratio. The largest tangible measure, as I have said, is the largest mountain on the earth's surface. Suppose such a mountain to be regularly shaped, and to have a diameter of twenty miles at the base, it would then contain 576 cubic or solid miles of material. Make use of that huge body as the unit of measurement of the bulk of the earth, and the bulk of the earth would contain it 450,000,000 of times, and even more. How can we appreciate so large a number? We find it even difficult to form an idea how large a number a million js; we may obtain some idea of the vastness of numbers, such as those in question, by ascertaining the time required to count them. If, then, you should count at the rate of two per second, continuing the work for eight hours a day, twenty-one years and five months would be spent in counting the number which expresses the bulk of the earth in comparison with that of the mountain. Perhaps I do not exaggerate the matter when I say, that the most accurate idea of a bulk so vast may be obtained by regarding the image which we frame to ourselves when we attempt to form an idea of infinite space. cannot grasp infinity this image must have a dim and misty outline; but it may be that it approaches more nearly than anything else to presenting an adequate idea of the actual size of the earth.

Having obtained some idea of the size of the earth let us proceed a step further, not in the way of doubling, but much faster. In so doing we next notice the distance of the earth from the moon, which is represented here on a much smaller scale than that employed in our first figure. The distance from the centre of the earth to the centre of the moon is about sixty radii, or thirty diameters of the earth. The magnificent appendage of Saturn compares very well in size with this, its diameter being about twenty times that of the earth. We pass from this to the diameter of the sun, which is about one hundred and twelve times that of the earth, and, of course, the surface is more than ten thousand times the surface of the earth. The scale we have at first adopted we should find to be inadequate to compare the earth with the sun. No ordinary apartment could contain the necessary illustration. The scale has therefore been reduced a thousand times, instead of being that of a hundred miles to a foot. This diagram is constituted on a scale of 100,000 miles to a foot. On it the earth has shrunk down to 1oof an inch in diameter. This, then, [pointing to the figure,] is the relative size of the sun, 112 diameters of the earth being equal to the diameter of the sun. The liveliest imagination, however exer

As we

cised, can form no adequate idea of the size of this magnificent luminary of the day. Its surface occupies an area greater than that of twice ten thousand oceans, each larger than the Pacific. And this surface is tossed into waves of intense brilliancy, beneath which the Himalayas would be buried and “melt with fervent heat ;” and whether we regard him as issuing from the chambers of the east, he commences like a giant to run his course; or whether in unveiled meridian splendor, he almost seems to pause a moment to gaze upon a world rejoicing in his presence, or enwrapped in robes of surpassing magnificence he sinks to rest at night; under any and all these points of view, he is at once the fitting representative and chosen emblem of all that is good and beautiful.

From the size of the sun we proceed, in the next place, to that of · the diameter of the earth's orbit. But I would observe, in passing, that the relative size of most of the planets is represented in this diagram. Thus, we have that of Mercury, Venus, Mars, Jupiter, Saturn, &c. The moon is represented by a ball, the size of a pea, at

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Upper line-1. Mercury. 2. Venus. 3. Earth. 4. Mars. 5. Moon. 6. Jupiter.

Lower line—7. Saturn and the three largest of his satellites. 8. Uranus, with the two large satellites. 9. Neptune, with his satellites. the place to which I now point, almost touching the sun. resents the comparative size of the moon. The distance from the centre to the surface of the sun is one and two-thirds the distance of the moon from the earth, which itself is thirty diameters of the earth.

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The distance of the earth from the sun is about 12,000 diameters of the earth, or, if we proceed in the other way, multiplying the last unit, we shall find it to be 107 diameters of the sun, vast as is that body in extent. To travel this distance at the rate of thirty miles an hour, going on continually, would occupy three hundred and sixty two years and seven months; and merely to count it at at the rate already mentioned, that of two per second for eight hours of every day, would fully occupy four and a half years ; and yet more than three times this distance the earth travels every year. To turn around but once in a year requires but a very slow angular motion. Imagine the hand of a dial-plate to turn around only once in a year, how large the dial-plate must be in order that we might see the motion at all; yet in completing its circuit the earth travels at the rate of nineteen miles per second; or, while I deliberately say to you, it moves, we are borne nineteen miles. This result cannot be in error by more than its two hundred and thirtysecond part. When nearest to the sun, which is about the last of December, we travel about three-tenths of a mile per second faster than this, and about the first of July three-tenths of a mile slower. Even this excess of velocity is fearful. Who could think of being conveyed, mechanically, over the surface of the earth at the rate of three-tenths of a mile per second.

We are now compelled again to reduce our scale, and, instead of one, one hundred thousand miles to the foot, make use of one, two hundred millions of miles to a foot; and thus the sun, though magnificent in comparison with the earth, shrinks down and becomes no larger than the head of a pin. The orbit of the earth is represented by a white curve, to which the rod now points. Here we have the disturbed regions of the smaller planets, and there we have portions of that of Uranus and the most remote of the known planets, Neptune. This long and complete curve is the orbit of Halley's comet. The distance of the earth from the sun being now taken as our unit, the distance of Neptune will be thirty times that, or thirty times ninetyfive million miles. Of course, to travel it at thirty miles per day continuously would occupy about ten thousand eight hundred and seventy-five years. Five distances of the earth from the sun from the place of Neptune would carry you to the end of the orbit of Halley's comet. The distance from this, again, to the nearest star is, we had almost said, a void of immense extent compared, with that which we have already had to do. It is scarcely worth while to regard miles at all in speaking of the distance of a star; the number becomes so large that we cannot grasp it. We may, however, obtain a speaking illustration of the enormous distance of the nearest of the fixed stars by ascertaining what must represent it in comparison with the small globe which I hold in my hand, which has a diameter of three inches. We must despair any more of illustrating distances so vast by any picture, however large. We are not about to deal in magnificent oriental fiction, but with ascertained facts. Let this globe represent the earth; then one hundred and seventeen thousand five hundred miles will represent the distance of the nearest fixed star.

It is useless, almost, to state how long it would take to count

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