by the Greek letter y. Some of the stars which are distinguished for their superior brilliancy, have particular names attached to them;-such as Sirius, in the right shoulder of the constellation Orion; Rigel, in his left foot; Arcturus, &c.

The principal fixed stars, which lie within a convenient distance of the Moon's path, are used for taking Lunar distances, in order to enable mariners to deduce their longitude. The distances of particular stars from the Moon, at certain regularly recurring times, when the Moon is visible, are calculated at Greenwich, and set down for some years in advance according to Greenwich time. As the motion of the Moon is quicker than that of any other heavenly body as seen from the Earth, these lunar distances soon change. If then a person on the ocean wishes to know his longitude, and he finds, for instance, that on such a day and hour, according to the Nautical Almanack, such a particular star is so many degrees distant from the Moon, but that this lunar distance occurs, as seen from the ship, an hour sooner than the Greenwich time :-in this case, his longitude is 15° W. If the recorded distance had occurred an hour later, his longitude would have been 15° E.

The stars beyond the 7th magnitude are called telescopic stars. Those, which are visible to the naked eye at any one time, are supposed not to exceed 2000, notwithstanding the countless assemblage which appears to be present. This results from a sort of optical delusion, whereby the eye is disconcerted by the apparent want of order; but, with the telescope, Sir William Herschel computed that a small portion of the heavens, not exceeding 15° in length, by 2o in breadth, exhibited not less than 50,000 stars, from which it has been cal

culated that the same instrument would make visible in the whole starry sphere, not less than 75 millions of stars! The mind shrinks within itself at the contemplation of such a vast array,—and still more, when it is considered that this number is limited by the imperfection of human contrivances; for there can be no doubt, that, if our telescopes were more powerful, the number of visible stars would be greatly increased. This observation may refer to that thin gauzy band of light, which seems to surround the dome of the heavens on a clear evening, when the Moon is absent. It has the name of the Galaxy, or Milky way. By the power of modern instruments this has been shown to be a vast congregation of stars so small, or so far off, that to an observer on our Earth they present only, by their association, a dim zone of light. The elder Herschel observed about 600 stars in his telescope at the same time, and they continued as numerous for a quarter of an hour. He reckoned up in one portion of the Milky way, about 250,000 stars.

The stars are always spoken of as being fixed; and if we regulate our expressions by the analogy of general movements, they are certainly fixed; but astronomers have of late years seen reason to believe that a very minute motion may be detected in some stars; that is, that a certain group of stars does not present the same relative distances between the stars of which it is formed at one time, as at another. These quantities of motion, or of difference, are, however, so inconceivably small, that they belong to the refinements of astronomy, and need not be discussed here.

But we have now to notice a very remarkable circumstance, which seems to afford evidence that the

stars are luminaries like our Sun, and have planets revolving round them; that each one

Informs a system in the boundless space,

And fills with glory its ap pointed place.

When the stars are observed with close attention by means of a good telescope, many of them are found to be double; that is, to consist of two smaller stars, the dark division between them being too faint to be distinguished in an ordinary observation. In some instances, this may occur from one star being almost directly behind another; and though at an immense distance off from the first, yet seeming to our vision to lie in the same line; but, in other instances, it is found that one star revolves round the other, or the two revolve round some point situated between them. Very little was known on this subject until of late years, when Sir William Herschel, and afterwards Sir J. South and Sir John Herschel, distinctly showed that such a revolving motion was perceptible: at one time the satellite, or smaller of the two stars, would disappear, as if it had passed round behind the other in the course of its motion, just as Jupiter or Venus is sometimes invisible to us, on account of being on the opposite side of the Sun; or the satellites of Jupiter, by passing round the body of that planet. There is a double star, marked & in the right hind foot of the constellation called the Great Bear, in which the two component stars revolve round each other in about 60 years; so that nearly a whole circuit has been performed since its discovery in 1781. About 3000 of these double stars have been observed, and formed into a catalogue, in which their positions, with respect to latitude and longitude, and the relative positions of the two component stars of each,