페이지 이미지

together in the same workshop, where they were reposed during the reparations.

FAUNA.- About this time' Mackarel begin to be taken in abundance on our southern coasts, particularly Brighton and Hastings. Some young birds of the early broods also are seen about, and are hardly recognized in their first plumage.

Tempus. Of the Period called Summer.-“Summer begins the 7th of the sixth month, June, and lasts 93 days. The mean temperature of the season is 60.66', or 11.72° above that of Spring. The medium of the twenty-four hours rises during the season from 58° to 65°, and returns again by the close to the former level.

The mean height of the barometer for Summer is 29.877 inches, or .045 inches above the vernal mean. The atmosphere now acquires, under the more vertical rays

of the Sun in full North declination, the greatest quantity of heat and vapour which it at any time contains, and it accordingly weighs most by the barometer. The range of this instrument still diminishes to the middle of the season, when it does not exceed an inch: it then gradually increases again to the end : the mean range 1.08 inches.”—Howard.

June 8. St. Medard Bp. C. St. Gildard. St. Mari

mius Bp. C. St. Clou. St. William of York. St. Syra Virgin.

URANIA.- On the Changes and probable Motion of the fixed Stars.-We shall today, in the absence of any particular calendarian subject, subjoin the following extracts from the papers of the late Dr. Herschel, the subject being one capable of exciting the most intense curiosity and interest. We have already alluded to the wonderful revolving star in Cassiopeia.

Dr. Herschel gives a short account of the most striking changes he had found to have happened in the heavens since Flamstead's time. He made three reviews of the heavens with telescopes of different powers, all of which are described in the Philosophical Transactions, but the objects which he chiefly attended to in the last review were, 1. The existence of the particular stars for which he was looking, and which had been noticed by former astronomers, and arranged in former catalogues. 2. To observe whether they were single or double, well defined, or hazy. 3. To view and mark down the particular colour, whenever the altitude and situation of the star would permit it to be done with certainty. 4. To examine all the small stars in the neighbourhood, as far, at least, as the twelfth magnitude, and note the particulars concerning them, except the colours, which would not be of any material use. The results of this survey will be as follow. Though our limits allow us to give but a very brief account of these results, yet it will, we trust, be such as to convey to our readers a very good idea of the author's discoveries; and for the details the reader is referred to vol. lxxii. of the Philosophical Transactions, or to the fifteenth of the Abridgment. Dr. Herschel notices,

1. Stars that are lost, or have undergone some capital change since the time of Flamstead. In the British catalogue are marked and described two remarkable stars, of the fourth magnitude, in the constellation of Hercules, viz. the 80th and 81st; but these are no longer visible, although sought after with the utmost diligence. In the northern claw of Cancer, Flamstead placed three stars of the sixth magnitude, viz. the 53d, 55th, and 56th of his catalogue. The latter of these is vanished.

The 19th Persei, a star of the sixth magnitude, is either lost, or so considerably removed from its place since Flamstead's time, that it is no longer to be known. The 26th Cancri is lost. The 62d Orionis is lost, and a star near the 54th and 5lst is not noticed by Flamstead. The 71st Herculis is lost. The 70th and 71st are so near each other by Flamstead's catalogue, that it cannot readily be told which is wanting. There is a telescopic star, within about 30 minutes north, following in a direction towards u Lyrae: if that should be the 71st, it is wonderfully changed both in size and place. The 34th Comae Berenices is lost, which Flamstead has marked as a star of the fifth magnitude. The 40th and 41st Draconis have undergone so great an alteration of place, that it cannot possibly be mistaken; for, in Flamstead's time, they were above three minutes asunder, but now their distance is less than half a minute.

2. Stars that have changed their magnitude since Flamstead's time.-Of these, the most remarkable of those noticed by Dr. Herschel are as follow: a Draconis is so much less than B, which is set down as a smaller star in Flamstead's catalogue, that the change cannot be doubted; B Ceti, marked of the 3d, and a Ceti of the 2d, are evidently the reverse, ß being by much the larger star.

y Lyrae is much larger than ß. The change in the magnitudes of the 31st and 34th Draconis is very striking; these two stars being just the contrary of what they are marked in Flamstead's catalogue.

3. Stars that are newly come to be visible. — Near Lacerta's tail end is a star of between the fourth and fifth magnitude, not mentioned in Flamstead's catalogue, though the 1st Lacertae, not far from that place, is recorded. The star of the fifth magnitude, following + Persei, is, most likely, new. A very considerable star, not marked by Flamstead, will be found near the head of Cepheus. A considerable star, in a direction from the 68th Geminorum towards the 61st, is not to be found in Flamstead. A star of a considerable magnitude, preceding the 1st of Equulei, is not in Flamstead's catalogue: it is a double star of the first class, the 61st of Dr. Herschel's second collection, where measures of it will be found.

Between B Cancri and & Hydrae is a very considerable star not noticed by Flamstead, though its situation is very remarkable. As the constellation of Cancer contains so rich a collection of very small stars, it is the more astonishing how a star of such consequence, if it then existed, could be omitted. About 3o_south, preceding y Bootes, is a considerable star, not in Flamstead's catalogue, of the sixth magnitude; and south, preceding ~, another almost as large.

Dr. Herschel, having stated these and many other facts of the same kind, inquires, which is the proper motion of the Sun and solar system; and he asks, Does it not seem very natural, that so many changes among the stars - many increasing in magnitude, while numbers seem gradually to vanish -- several of them strongly suspected to be newcomers, while we are sure that others are lost out of sight the distance of many actually changing, while many more are suspected to have a considerable motion;- does it not seem natural that these observations should cause a strong suspicion that, most probably, every star in the heavens is more or less in motion? Though we have no reason to think that the disappearance of some stars, or new appearance of others, nor, indeed, the frequent changes in the magnitudes of so many of them, are owing to their change of distance from us by proper motions, which could not occasion these phenomena without being inconceivably quick; yet we may well suppose that motion is, in some way or other, concerned in producing these effects. A slow motion, for instance, in an orbit round some large opaque body, where the star, lost or diminished in magnitude, might undergo occasional occultations, would account for some of those changes; while others might, perhaps, be owing to the periodical return of large spots on that side of the surface which is alternately turned towards us by a rotatory motion of the star. The idea also of a body much flattened by a quick rotation, and having a motion similar to the Moon's orbit, hy a change of the place of its nodes, by which more of its luminous surface would, at one time, be exposed to us than another, tends to the same end. Now, if the proper motion of the stars, in general, be once admitted, who can refuse to allow that our Sun, with all its planets and comets, that is, the solar system, is no less liable to such a general agitation as we find to obtain among all the rest of the celestial bodies ? Admitting this, the greatest difficulty will be, how to discern the proper motion of the Sun among so many other and variously compounded motions of the stars. To obtain this, Dr. Herschel has laid a good foundation, from which he infers, that, if the solar system be carried towards any star situated in the ecliptic, every star, whose singular distance in antecedentia, reckoned on the ecliptic from the star towards which the system moves, is less than 180 degrees, will decrease in longitude ; and that, on the contrary, every star, whose distance from the same star, reckoned upon the ecliptic, but in consequentia, is less than 180 degrees, will increase in longitude.

In applying this theory to facts relating to the proper motion of the stars, Dr. Herschel says, astronomers have already observed what they call a proper motion in several fixed stars, and the same may be supposed of them all. We ought, therefore, to resolve that which is common to all the stars, which are found to have what has been called a proper motion, into a single real motion of the solar system, as far as that will answer to known facts; and only attribute to the proper motion of each particular star the deviations from the general law which the stars seem to follow in those movements. By Dr. Maskelyne's account of the proper motion of some principal stars, we find Sirius, Castor, Procyon, Pollux, Regulus, Arcturus, and a Aquilae, appear to have certain motions in right ascension, and two of them, viz. Sirius and Arcturus, in declination southward. Dr. Herschel assuming a certain direction, and supposing the Sun to move in that direction, he then takes for granted that one motion will answer for that of all the stars together; for if the supposition be true, Arcturus, Regulus, Pollux, Procyon, Castor, and Sirius, should appear to decrease in right ascension, while a Aquilae, on the contrary, should appear to increase. Again, suppose the Sun to ascend at the same time in the same direction towards some point in the northern hemisphere, for instance towards the constellation Hercules; then will also the observed change of declination of Sirius and Arcturus be resolved into the single motion of the solar system. Dr. Herschel farther observes, that the concurrence of those seven principal stars must give value to an hypothesis which will simplify the celestial motions in general. “We know that the Sun, at the distance of the fixed stars, would appear like one of them, and, from analogy, we conclude the stars to be suns. Now, since the apparent motions of these seven stars may

be accounted for, either by supposing them to move just in the manner they appear to do, or else by supposing the Sun alone to have a motion in a direction, somehow not far from that above assigned to it, we are no more authorized to suppose the Sun at rest, than we should be to deny the diurnal motion of the Earth, except, in this respect, that proofs of the latter are very numerous, whereas the former rests only on a few though very capital testimonies.”

Although Dr. Herschel mentions the motions of those seven principal stars, as being the most noticed and best ascertained of all, yet he adduces a farther confirmation of the same from other stars; by referring to and transcribing the following table of the proper motion of 12 stars, both in right ascension and declination, in 50 years :

[ocr errors][ocr errors][merged small][merged small][merged small][ocr errors]

All these are in the northern hemisphere, except Sirius. Regulus being added to the number, and Castor being double, we have fourteen stars, to all of which, except to Regulus, is assigned a motion in declination, as well as in right ascension; so that we have no less than 27 motions given to account for. Now, by assuming a point somewhere near a Herculis, and supposing the Sun to have a proper motion towards that part of the heaven, most of these are accounted for: for B'Cygni, a Aquilae, Cygni, y Piscium, y Arietis, and Aldebaran, ought, on the supposed motion of the Sun, to have an apparent progression, or to increase in right ascension, while Arcturus, Regulus, the two stars a Geminorum, Pollux, Procyon, Sirius, and y Geminorum, should apparently go back, so as to decrease in right ascen

« 이전계속 »