ings suffice to show that such is not the case with the Moon: at one time a crescent only is seen, whose hollow side is towards the left of the observer; at another time the hollow side is towards the right: the crescent sometimes enlarges to a perfect circle; which at other times contracts from a circle to a crescent. If, then, the Moon be a ball or globular body, shedding light upon the Earth, there is great difficulty in conceiving what can occasion the change in its apparent shape; but, if we were to consider the Moon to be an opaque or nonluminous body, we should find the means of explaining the change in its apparent figure, by supposing that the Sun shines upon the Moon, and that it is only by the reflection of the Sun's light from the Moon that the Moon becomes visible to us. If we place a large round ball on a table, in a place where the Sun is shining, we shall see the ball more or less illuminated, according to our position with regard to the ball and the Sun: in one position, the ball will appear to be equally divided by a boundary line, into two semicircles, one illuminated and the other in the shade: in another position, the illuminated portion will be only a crescent, all the rest being shaded: from another point again it will all appear illuminated, except a small crescent of shade. If the observer watch the relative positions of the Sun and Moon, he will see that the shape of the bright part of the Moon depends on its relative position in respect of the Sun; just as the bright portion of the illuminated ball depended on the position in which he viewed it.

We should in this way find the means of accounting for the change in the shape of the Moon. We shall, by and bye, show that these suppositions are really true. But another point would attract the notice of

the observer, independently of the change in apparent form. If the two brilliant bodies, the Sun and Moon, were observed to be near each other on a certain day when the latter appeared as a thin crescent to the left of the Sun, they would be seen the next day further removed, and on the following day, at a still greater distance from each other: if, therefore, the motion of the Moon round the Earth be admitted, it is necessary to suppose that motion to be slower than the Sun's motion round the Earth.

But in addition to the glowing light of the Sun and Moon, a glittering assemblage of smaller bodies meets the eye of the observer: a crowd of little spangles adorns the sky when the Sun has left it, and softens the dreary darkness which results from his absence. These stars are seen to resemble the Sun and Moon in the circumstance of rising in or near the east, attaining a certain altitude, and setting in the west; from which circumstance the observer infers that the stars, like the Sun and Moon, revolve round the Earth. But, by a careful attention to different stars, he would find that the same remark does not apply to all. Those which rise exactly in the east, set exactly in the west; those which rise to the south of east, set south of west; and many which rise somewhat north of east, set somewhat north of west; but in looking northward he sees stars which appear neither to rise nor to set, but which perform a complete circle round a particular point of the heavens. For example, there are seven stars, which, to most persons who pay any attention to the appearance of the heavens, are known under the name of the Great Bear. These stars never rise or set to an inhabitant of London. If they become invisible, it is either

because clouds obscure them, or the superior brilliancy of the Sun drowns their comparatively feeble light. The same may be said of five conspicuous stars known by the name of Cassiopeia's Chair.

If we watch the progress of these stars, and others in their vicinity, we shall find that they describe a circle round a star called the Pole-star. The position of this star we shall find to be nearly this: if we suppose the distance from the north point of our horizon (which is the line in which the surface of the earth appears to touch the sky) to the zenith (which is the point immediately over our heads) to be divided into five equal parts, then at about the height of three of those parts from the earth, will be seen the Pole-star.

All this would seem to show to an observer, that the Pole-star is the end of an axis round which all the stars revolve, and that the reason why we cannot see the whole circular path of any stars except of those in the vicinity of the Pole-star, is, that they pass round under the Earth during a part of their journey, and are therefore concealed from our view. Those stars which are further removed from the Pole-star describe larger circles than those which are nearer, while the Pole-star is almost stationary. This is exactly what takes place when we see a wheel turn round; the axle remains in one spot, but any particular point on the outer edge of the wheel describes a larger circle than that which is described by any point between the axle and the circumference.

If we consider the Pole-star to form one end of the axle or axis round which the stars revolve, then it is obvious that there must be an opposite end of the same axis, in the contrary direction. If then we turn to

12

RELATIVE DISTANCES OF THE STARS.

wards the south, with the expectation of seeing such a point, we shall find that it will not be realized; for none of the stars in that quarter are seen to describe circles; for they all rise and set. Still, however, the semicircles or portions of semicircles, commonly called arcs, which they describe, appear to have a common centre, which is some distance below the horizon; and this centre may be considered as the southern end of the axis before spoken of.

If we suppose the observer to have arrived at this amount of information respecting the stars, he will be prepared to notice the uniformity of the positions of the stars with respect to one another. The Great Bear, for instance, whether it be under or over the Pole-star, or at the right or the left of it, will always have its seven principal stars at the same relative distances from each other. The changes which take place in the distance of the sun from the moon, would lead to the opinion that these revolve round the earth in unequal times; and by similar reasoning, the constant maintenance of the same distance between any two stars would seem to imply that the stars revolve in equal times.

The seeming myriads of stars which present themselves to the notice of the observer all appear to follow this rule, of remaining at the same relative distances from one another, with very few exceptions. These exceptions are, indeed, so few, that a constant watching of the same part of the heavens for a considerable period would be necessary to determine that a star had actually changed its place relatively to other stars. There have, however, been discovered at different times,

ten stars, more or less brilliant, which change their relative distances from one another, and from other stars. These we know by the name of Planets; and by a careful attention to their movements, it is seen that each one travels in a curved path among the other stars, and returns again nearly to the point from whence it set out.

At intervals, again, star-like bodies of another order present themselves, whose progress among the other stars is more rapid than that of the planets; and which, at a period more or less brief, vanish altogether from the view of the observer, and do not return till after a long absence. To such bodies we give the name of Comets.

Such, then, are the equally sublime and fascinating appearances which present themselves to the eye of an observer, when that eye is directed towards the heavens. That the invigorating and fructifying warmth and light shed by the sun,-the serene, quiet light of the moon, —and the diamond-like glittering of the stars,-should invite men to a study of the laws which, under their Divine Creator, govern the motions of such exquisite globes of light, is what we are not only prepared to expect, but fancy that we should feel disappointment in finding it otherwise. Man is not, by nature, the cold heartless being who can let such beauties pass unheeded; and if he approach the study with the humility which true self-knowledge is calculated to engender, he becomes more and more able to appreciate the surpassing grandeur and power of the great Being who made and who rules all. Well, indeed, may we direct our attention to the phenomena which we have