verted to Christianity, which she afterwards professed with the utmost intrepidity, openly reproving the pagans for offering sacrifices to their idols, and upbraiding the Emperor Maxentius, to his face, with the most flagrant acts of tyranny and oppression. She was condemned to suffer death by rolling a wheel over her body stuck round with iron spikes.

27.-ADVENT SUNDAY.

This and the three subsequent Sundays, which precede the grand festival of Christmas, take their name from the Latin advenire, to come into, or from the word adventus, an approach.

30.-SAINT ANDREW.

Andrew was the son of James, a fisherman at Bethsaida, and younger brother of Peter. He was condemned to be crucified on a cross, of the form of an X; and, that his death might be more lingering, he was fastened with cords.

The Order of the Thistle was instituted by Achaius, King of Scotland, in 787, restored by James V, 1540, revived by King James II, in 1687, and re-established by Queen Anne, in 1703.-See T. T. for 1815, P. 303.

History of Astronomy.

[Continued from p. 300.]

Astronomy of Modern Europe.

In another paper on the Construction of the Heavens, Dr. Herschel assumes, as a matter of fact, that the milky way is a most extensive stratum of stars of various sizes, and that our Sun is actually one of the heavenly bodies belonging to it; for he had viewed and gauged this shining zone in almost every direction, and found it composed of stars whose number constantly increased and diminished in proportion to its apparent brightness to the naked eye. To develope the ideas of the universe, suggested by his late ob

servations, he thought it best to take the subject from a point of view at a considerable distance both of space and of time.

In his theoretical view, he supposes numberless stars of various sizes scattered over an indefinite portion of space, in such a manner as to be almost equally distributed throughout the whole of course, the laws of attraction, which, no doubt, extend to the remotest regions of the fixed stars, will operate in such a manner as, most probably, to produce the following remarkable effects.

Formation of Nebula.-1. If the stars are of various sizes, it will frequently happen that a star, being considerably larger than its neighbouring ones, will attract them more than they will be attracted by others that are immediately around them, by which means they will be, in time, as it were, condensed about a centre, or form themselves into a cluster of stars, of almost a globular figure, more or less regularly so, according to the size and original distance of the surrounding stars.

2. The next case, which will also happen almost as frequently as the former, is, where a few stars, though not superior in size to the rest, may chance to be rather nearer each other than the surrounding ones, for in this case there will be formed a prevailing attraction in the combined centre of gravity of them all, which will occasion the neighbouring stars to draw together; not indeed so as to form regular or globular combinations, but yet in such a manner as to be condensed towards the common centre of gravity of the whole irregular cluster. This construction admits of the utmost variety of shapes, according to the number and situation of the stars which gave rise to the condensation of rest.

3. From the composition and repeated conjunction of both the foregoing forms, a third may be derived, when many large stars, or combined small ones, are situated in long extended, regular, or crooked rows,

hooks, or branches; for they will also draw the surrounding ones, so as to produce figures of condensed stars coarsely similar to the former which gave rise to

these condensations.

4. Other combinations may be admitted; when, for instance, a cluster of stars is forming in one part of space, there may be ar.other collecting in a different, but perhaps not far distant quarter, which may occasion a mutual approach towards their common centre of gravity.

5. As a natural consequence of the former cases, there will be formed great cavities, or vacancies, by the retreat of the stars towards the various centres which attract them; so that, on the whole, there is evidently a field of the greatest variety for the mutual and combined attractions of the heavenly bodies to exert themselves in.

The author is well aware that there are seeming objections to the principles here laid down, and he takes care to obviate them: it may seem, then, that such a system, as that described, would evidently tend to a general destruction, by the shock of one star's falling on another. In answer to this it is said, that if observation should prove this really to be the system of the universe, there is no doubt that its great Author has amply provided for the preservation of the whole, though it should not appear to us in what manner this is effected. Dr. Herschel likewise points out several circumstances that manifestly tend to a general preservation; as the indefinite extent of the sidereal heavens, which must produce a balance that will effectually secure all the great parts of the whole from approaching to each other. There remains, then,' says he, only to see how the particular stars belonging to separate clusters will be preserved from rushing on to their centres of attraction. And here I must observe, that though I have before, by way of rendering the case more simple, considered the stars as being originally at rest, I intended not to

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exclude projectile forces; and the admission of them will prove such a barrier against the seeming destructive power of attraction, as to secure from it all the stars belonging to a cluster, if not for ever, at least for a million of ages. Besides, we ought, perhaps, to consider such clusters, and the destruction of now and then a star, in some thousands of ages, as perhaps the very means by which the other parts are preserved and renewed. These clusters may be laboratories of the universe, wherein the most salutary remedies for the decay of the whole are prepared.'

The author next proceeds, and says, 'We will now retreat to our own retired station, in one of the planets attending a star in its great combination with numberless others; and, in order to investigate what will be the appearances from this contracted situation, let us begin with the naked eye. The stars of the first magnitude being, in all probability, the nearest, will furnish us with a step to begin our scale; setting off therefore with the distance of Sirius or Arcturus, for instance, as unity, we will at present suppose, that those of the second magnitude are at double, and those of the third at treble the distance, and so forth. It is not necessary critically to examine what quantity of light or magnitude of a star entitles it to be estimated of such or such a proportional distance, as the common coarse estimation will answer our present purpose as well: taking it, then, for granted that a star of the seventh magnitude is about seven times as far as the first, it follows, that an observer, who is inclosed in a globular cluster of stars, and not far from the centre, will never be able, with the naked eye, to see to the end of it; for since, according to the above estimation, he can only extend his view to about seven times the distance of Sirius, it cannot be expected that his eyes should reach the borders of a cluster which has, perhaps, not less than fifty stars in depth every where around him.

The whole universe, therefore, to him will be comprised in a set of constellations, richly ornamented with scattered stars of all sizes; or, if the united brightness of a neighbouring cluster of stars should, in a remarkably clear night, reach his sight, it will put on the appearance of a small, faint, whitish, nebulous cloud, not to be perceived without the greatest attention. To pass by other situations, let him be placed in a much extended stratum, or branching cluster of millions of stars, such as may fall under the third form of nebulæ, considered in a foregoing paragraph. Here, also, the heavens will not only be. richly scattered over with brilliant constellations, but a shining zone, or milky way, will be perceived to surround the whole sphere of the heavens, owing to the combined light of those stars which are too small, that is, too remote to be seen. Our observer's sight will be so confined, that he will imagine this single collection of stars, of which he does not even perceive the thousandth part, to be the whole contents of the heavens. Allowing him, now, the use of a common telescope, he begins to suspect that all the milkiness of the bright path which surrounds the sphere may be owing to stars. He perceives a few clusters of them in various parts of the heavens, and finds also that these are a kind of nebulous patches; but still his views are not extended so far as to reach to the end of the stratum in which he is situated; so that he considers these patches as belonging to that system, which, to him, seems to comprehend every celestial object. He now increases his power of vision, and, applying himself to a close observation, finds that the milky way is, indeed, no other than a collection of very small stars. He perceives that those objects which had been called nebulæ, are evidently nothing but clusters of stars. He finds their number increase on him, and, when he resolves one nebulæ into stars, he discovers ten new ones, which he cannot resolve. He then forms the idea of