serene night, and now the stars, which the brilliancy of day had eclipsed, shine forth in all their splendor, and perhaps that fairest one of them all, the evening star, adorns the western sky. As we look over the heavens, we notice here and there a group, or as the astronomer calls them, a constellation, with which we have been familiar from childhood. If we look upon the winter sky, we recognize Orion, with his bright belt, and the Pleiades or seven stars, or turning to the north, the great dipper or Charles' wain, being a part of the constellation “ Ursa Major," or the "Great Bear." As the eye wanders over these familiar objects, another sight bursts upon the delighted vision. The full-orbed moon rises majestically over the eastern hills, and in the increasing light, the lesser stars fade away. The evening star, no longer brilliant, is now ready to set below the western horizon, and stars, which at the commencement of night, were to the east of the meridian, are now in the mid heaven. If we turn to the north we find a change there, the cluster or group called the dipper, which we will suppose, at the commencement of our observation was almost parallel with the horizon, as shown in this figure, has moved

Polestar

eastward, and evidently performed a part of a revolution about some unknown centre. If we prolong our observations we find this group, and all the rest of the heavens apparently revolving around one star, which seems not to move at all. This star is called the pole, or polar star, and is nearly in a line with the two bright stars at the end of the dipper as shown at a and b in the above diagram, and about five times their distance, from the nearest one. Meanwhile, the lunar orb, with all its beautiful diversity of

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light and shade, ascends the heavens, reaches the highest point and declines in the west. Star after star sinks beneath the western hills, and new ones rise in the east. Twelve hours pass away, when again the sun, rising with undiminished lustre, calls the busy world once more into bustle and activity.

The phenomena thus presented, convince us that there is no such thing as rest, for the whole heavens seem revolving around us, and the first step towards an accurate knowledge of our earth is, that either we, or the heavenly bodies, are in ceaseless and regular motion.

Suppose that before us the waters of some vast lake or ocean are spread out; far as the eye can reach there seems to be a place where the sky is resting upon the water, called the horizon from a Greek word meaning "to see." As we stand, perhaps wondering how far from us this horizon is, a vessel sails out the harbor and moves steadily from us. Now our first idea is that we are looking out upon a vast plain, and consequently we expect to see the vessel as it moves away, become fainter and fainter, until at last the straining eye will fail to catch the minute image. This appearance is shown in the engraving below.

Instead of this, however, a new and unexpected phenomenon greets the eye. The vessel sails away, and soon arrives at the horizon, and then slowly sinks from view. First the hull disap

pears, then the sails, and at last the flag, presenting the appearance shown in this engraving.

This then is the second step towards obtaining an accurate knowledge of our earth, and we learn that the surface of our lakes, and seas, is not an extended plain, but curved. If we were on a vessel at sea, we would perceive the horizon encompassing us like a vast circle, of which, we would be the centre. And in whatever direction we made an observation, we would find the surface of the water curving or bending from us in that direction. The same phenomenon is observed on land. If we ascend some high elevation, such as a mountain, or lofty monument, the horizon appears in every direction equally distant, or, in other words, a large circle, of which we are the centre. From this we rightly infer that the surface of the earth is convex, like the surface of an apple, or an orange. It becomes an interesting question, after the convexity of the earth is thus established, to determine its actual shape, whether it is a true sphere, or a spheroid, i.e., having the diameter through one direction longer than another, or, whether the curvature is of such a nature as to return into itself, for it is well known that there are curves, such are the parabola, and hyperbola, which, however far continued, never return into themselves like the curve of a circle. It was therefore a bold undertaking to circumnavigate the globe and thus demonstrate its spherical form, by actually sailing around it. This was accomplished however by Ferdinand Magellan, or rather by the expedition which he fitted

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out, for he himself did not live to witness the complete triumph of his bold attempt. Magellan was a Portuguese who had entered into the service of Spain. In the year 1519 he sailed for South America, and discovered the straits called by his name, and which separate the island of Terra del Fuego from the continent. He likewise discovered the Marian and Phillipine islands, which he took possession of in the name of the King of Spain, and was killed on one of the latter group. His fleet was mostly dispersed, but one ship with eighteen men, returned to Spain in 1522, having sailed westward completely around the world. The rotundity of the earth, by these means, was established beyond a doubt, though indeed this proof was not necessary, a great variety of phenomena giving the same result. For example, the shadow of the earth, which is cast upon the moon at the time of a lunar eclipse, is always bounded by a curved line or circle, and it can be shown mathematically, that a spherical form is absolutely necessary for the stability of the earth. The moon, and all the planetary bodies, are also observed to present discs, the same as a ball suspended in the sky. Having learned these two things, viz: that there is a great and unceasing motion somewhere, and that the earth is round, it becomes interesting to determine its actual size, its diameter and circumference. Previous to determining this and on the supposition that our earth is the grand centre of the unilet us study the phenomena presented by the sun, planets, and stars in their apparent diurnal or daily revolution around the earth, premising however, that to certain directions upon its surface the arbitrary names, North, South, East, and West, have been assigned. For example, we call the part towards the north star north, the opposite south, and facing towards the north star, we call the right hand east, and the left hand west. These names are entirely arbitrary, i. e., they do not actually represent fixed directions in space, but are simply relative expressions, thus, what is east to one observer, may be west to another, for example, take the next diagram, representing the earth as round, the north pole being at the position N, and suppose two observers one at A, and the other at B, both facing towards the north.

verse,

If questioned about some object C, B would declare it to be

west, being at his left hand, whilst A would assert it to be east,

B

being at his right hand. The terms therefore, north, south, east and west, are only relative expressions, and not absolute directions. It will be necessary to remember this, and we may also remark, the same is true of the expressions up, and down. What would be up to an observer at A, would be in the direction N A, but this would be down to an observer at B. Hence we must learn to consider up, as away from the earth, and down as the direction to its centre, and therefore not absolute directions in space but only relative terms. Now as the sun and the stars are observed after certain regular intervals to appear in the east, apparently move over the heavens, and set in the west, the natural inference is, that they are revolving in vast circles around the earth, which itself is the immovable centre. Below we have given