That which appears only a single star in Orion's sword, Huygens found, by the telescope, to consist of 12 stars very near together. Galileo found 80 in the belt of Orion's sword, 21 in the nebulous star of his head, and about 500 in another part of the constellation within the compass of one or two degrees, and more than 40 in the nebulous star Præsepe. Others, even in the best telescopes, appear still as small luminous clouds. There is a very remarkable one in the constellation Orion, which the best telescopes show as a spot uniformly bright. It is a singular and beautiful phenomenon.

So great is the number of telescopic stars in some parts of the milky way, that Dr. Herschel observed 588 stars in his telescope at the same time, and they continued equally numerous for a quarter of an hour. In a space of about 10 degrees long, and 25 degrees wide, he computed 258,000 stars. Phil. Trans. 1795.

2. The appearance of the stars seen in a telescope, is very different from that of the planets. The latter are magnified and show a visible disc. The stars appear with an increased lustre, but with no disc. Some of the brighter fixed stars appear most beautiful objects, from the vivid light they exhibit.

Dr. Herschel tells us that the brightness of the fixed stars, of the first magnitude, when seen in his largest telescope, is too great for the eye to bear. When the bright star Sirius was about to enter the telescope, the light was equal to that on the approach of sun-rise, and upon entering the telescope, the star appeared in all the splendour of the rising sun, so that it was impossible to behold it without pain to the eye.

The apparent diameter of a fixed star is only a deception arising from the imperfections of the telescope. The brighter stars appear sometimes in bad telescopes to subtend an angle of several seconds, and this has led astronomers angle into mistakes respecting their apparent diameters.

The more perfect the telescope, the less this irradiation of light. We know with certainty that some of the brighter stars do not subtend an angle of 1", from the circumstance of their instantly disappearing, on the approach of the dark edge of the moon. Dr. Herschel attempted to measure the diameter of Vega in Lyra, and imagined it to be about of a second.

That the diameter of the sun may appear less than a

second, it must be removed 1900 times farther from us than at present; which is an argument in favour of the vast distance of the fixed stars.

Although the superior light of the sun effaces that of the stars, yet by the assistance of telescopes we can observe the brighter stars at any time of the day. The aperture of the telescope collects the light of the star, so that the light re ceived by the eye, from the star, is greater than when the eye is unassisted. The darkness in the tube of the telescope also in some measure assists. See Dr. Brinkley's Astronomy.

3. Some stars appearing single to the naked eye, when examined with a telescope, appear double or triple; that is, consisting of two or three stars very close together: such are Castor, a Hercules, the Pole Star, &c. Seven hundred, not noticed before, have been observed by Dr. Herschel.

In viewing these double stars a singular phenomenon discovers itself, first noticed ly Dr. Herschel; some of the double stars are of different colours, which, as the images are so near each other, cannot arise from any defect in the telescope. a Herculis is double, the larger red, the smaller blue; & Lyræ is composed of four stars, three white and one red; y Andromedæ is double, the larger reddish white, the smaller a fine sky blue. Some single stars evidently differ in their colour. Aldebaran is red, Sirius a brilliant white.

From a series of observations on double stars, Dr. Herschel has found that a great many of them have changed their situations with regard to each other; that the one performs a revolution round the other, and that the motion of some is direct, while that of others is retrograde. He has observed that there is a change in more than 50 of the double stars, either in the distance of the two stars, or in the angle made by a line joining them with the direction of their daily motion.

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The wing are the observations that have been published relative to six double stars, a Gemenorum, (Castor,) Leonis, & Botes, & Herculis, & Serpentis, y Virginis. In respect to Castor, the first of these, Dr. Herschel thinks it highly probable, that the orbits in which the two stars move round their common centre of gravity are nearly circular, and at right angles to the line in which we see them; and that the time of a whole apparent revolution of the small star round Castor will be nearly 342 years and 2 months, in a retrograde direction.

Of the two stars which compose y Leonis, the smaller one revolves round the larger in an apparent elliptical orbit, and performs a retrograde revolution in 1200 years.

The beautiful double star, & Bo tes, is composed of 2 stars, one of which is of a light red, and the other of a fine blue, having the appearance of a planet and its satellite. From observation Dr. Herschel concludes, that the orbit of the small star is elliptical, and performs its revolution, according to the order of the signs, in 1681 years.

The double star, (Herculis is composed of a greater and lesser star; the former being of a beautiful bluish-white, and the latter of a fine ash colour. The smaller one revolves round the larger, nearly in the plane of the spectator. On the 11th of April, 1803, it was nearly occulted by the larger star.

The double star, & Serpentis, has, like & Bootes, undergone a considerable change in the angle of position, without any variation in the distance between the two stars. Dr. Herschel computes the period of the smaller star round the larger to be 375 years.

The double star, y Virginis, which has long been known to astronomers, is composed of two nearly equal stars; the smaller, according to Dr. Herschel, completes its revolution in about 708 years.

When we take into consideration the very small angle which the apparent distance of these double stars subtends, and the slow motion of the revolving stars, we must conclude that the period of their respective revolutions cannot be ascertained with any great degree of accuracy. Squire's Astronomy.

4. From former observations, it appears considerable changes have taken place among the fixed stars. Stars have disappeared, and new ones have appeared.

The most remarkable new star recorded in history, was that which appeared in 1572, in the chair of Cassiopeia. It was for a time brighter than Venus, and then seen at midday: it gradually diminished its lustre, and after 16 months disappeared. That the circumstances of this star were faithfully recorded we can have no doubt, since many different astronomers of eminence saw and described it. Cor nelius Gemma viewed that part of the heavens, the sky

being very clear, and saw it not. The next night it appeared with a splendour exceeding all the fixed stars, and scarcely less bright than Venus. Its colour was at first white and splendid, d. afterwards yellow, and in March, 1573, red and fiery like Mars or Aldebaran; in May of a pale livid colour, and then became fainter and fainter till it vanished.

Another new star, little less remarkable, appeared in Oct. 1604. It exceeded every fixed star in brightness, and even appeared larger than Jupiter. Kepler wrote a dissertation on it. Changes have also taken place in the lustre of the fixed stars; Aquilæ is now considered less bright than y. A small star near ( Ursa Majoris is now probably more bright than formerly, from the circumstance of its being named Alcor, an Arabic word, which signifies sharp-sightedness in the person who could see it. It is now very visible.

Several stars also change their lustre periodically. o Ceti, in a period of 333 days, varies from the 2d to the 6th magnitude. The most striking of all is Algol, or 8 Persei. Goodricke has with great care determined its periodical variations. Its greatest brightness is of the 2d, and least of the 4th magnitude; its period is only 2 days, 21 hours: it changes from the 2nd to the 4th magnitude in 34 hours, and back again in the same time, and so remains for the rest of the 2d. 21 hours. These singular appearances may be explained, by supposing the fixed star to be a body revolving on an axis, having parts of its surface not luminous.

The following are some of the most remarkable variable stars, viz :

New star of 1572 in Cassiopeia, which changes from the 1 to 0; that is, from the first magnitude to be invisible; period 150 years.

• Of the Whale, from 2 to 0; period 333 days.

New star of 1604, in the east foot of Serpentarius, from 1 to 0; period not known.

ẞ Lyræ, from 3 to 5; period 6 days, 9 hours.

New star of 1670, in the Swan's head, which has not been seen since 1672.

η Antinoi, from 3 to 5; period 7 days, 4 hours, 15 minutes. x In the Swan's neck, from 5 to 0; period 369 days, 21 hours.

Another in the same constellation, near y in the breast; from 3 to 0; period 18 years.

d Chephei, from 3 to 5; period 5d. 8h. 37 m.

Some stars, like ẞ in the Whale, have gradually increased in brilliancy; others, like d in the Great Bear, have been constantly diminishing in brightness.

5. The number of nebulæ is very considerable. Dr. Herschel has discovered above 2000: before his time only 103 were known. But far the greater part of these 2000 can be seen only with telescopes equal to his own.

He has given an account of several phenomena, which he calls nebulous stars, stars surrounded with a faint luminous atmosphere. He describes one observed Nov. 13, 1790, in the following manner. A most singular phenomenon : a star of the Sth magnitude, with a faint luminous atmosphere, of a circular form, and of about 3' diameter; the star is exactly in the centre, and the atmosphere is so diluted, faint, and equal throughout, that there can be no surmise of its consisting of stars; nor can there be a doubt of the evident connexion between the atmosphere and the star. Another star, not much less in brightness, and in the same field wit the above, was perfectly free from any such appearance.

6. As the earth moves in an orbit, nearly circular, round the sun, an observer on its surface in one situation, is nearer some stars by the diameter of the earth's orbit, than in another, and consequently the angular distances of those stars ought to appear greater. But the angular distances of the fixed stars, observed at different seasons of the year, always remain the same, even when observed with the most exquisite instruments. Hence, the diameter of the earth's orbit, which is about 190 millions of miles, bears no sensible proportion to their distance.

The greatest angle which the diameter of the Earth's orbit subtends at any fixed star, is called its annual parallax, and sometimes only parallax.

According to the observations of Dr. Bradley, the annual parallax of y Draconis, a star of the second magnitude, situate nearly in the solstitial colure, about 150 from the pole of the ecliptic, is imperceptible. The observations of Pond, the present astronomer at Greenwich, and those of Dr