« PreviousContinue »
brilliancy or particular location were rendered peculiarly serviceable, received particular names, for their more perfect identity, or from mere caprice. This was done at a period so remote as to be now lost; yet we continue both the divisions and the names, at the present day. In the book of Job, and again in Amos, we find these divisions recognised ; and many of the early poets make mention of them. Numbers of the fixed stars are now known to revolve in proper orbits around each other; but still they are termed fixed, because to the unassisted eye, they suffer no change of position with regard one to another.
It was to this class of heavenly bodies that Uranus, until the year 1781, was supposed to belong. Being visible to the naked eye, it was probably seen by millions of the human family, in the earlier ages. of the world; but it was seen only as one of the countless gems that immovably deck the celestial vault.
When astronomy had so far advanced as to render accurate catalogues of the fixed stars desirable, the compilation of such was undertaken; and Uranus must of necessity have had a place in each of these which embraced stars of so low a magnitude, unless overlooked by inadvertence: in several it certainly appeared.
Observations made by Flamstead, an English astronomer, record the position of this body in the heavens, in the year 1690; and at several other periods. Mayer, a native of Maspach, in Wurtemberg,
of the greatest astronomers, not only of the 18th century, but of any age or any country, (says Delambre,) in his new catalogue of zodiacal stars, for 1756, has inserted it as star No.964. Bradley, an Englishman, also observed and noted this body as a fixed star, in 1753. Lemonnier, a French astronomer, first observed and noted Uranus, as a fixed star, in 1765; and his manuscripts, now at the Royal Observatory of Paris, show no less than twelve observations, upon the same planet. In all these instances no opinion was entertained, by any one of the observers, that this particular body differed in any respect, from those by which it was surrounded ; and the fact of its identity with these was first suspected by finding no star in either of the several places where stars had been designated, in the maps; and such suspicions were subsequently verified by calculations thai show it to have occupied the respective positions thus assigned, at the stipulated periods of time.
As no planet was suspected to exist beyond Saturn, so none was sought for there; nor had the discovery of motion, in Uranus, the most distant connexion with any preconceived intention of such discovery: it was the result of accident alone. Herschel, (father of the present English astronomer, now observing at the Cape of Good Hope,) a native of Hanover, had established himself in England, where he had been some years engaged in the construction of telescopes, through mere curiosity and a taste for astronomy. These instruments he applied to use, as he completed them, and thus became a highly creditable and able practical observer. On the night of the 13th of March, 1781, while engaged in a series of observations upon the parallax of the fixed stars, and regarding with attention several small ones, near the feet of Gemini, he was struck with the fact that one appeared larger than the rest, when seen in his telescope. As He gave
the fixed stars are not materially magnified by these instruments, the fact of this enlarged appearance, when once detected, fixed the observer's attention. The telescope with which this discovery was made was one of seven feet in length only, and the eye-piece in use at the moment was one which magnified two hundred and twentyseven times. Having, by subsequent observations, determined that the star in question had changed place, in relation to those by which it was surrounded, Herschel no longer concealed his discovery. Still he had no suspicion he had discovered a planet: he wrote to the Royal Society, of which he was a member, stating the facts, and adding that his first impression was he had detected a small comet, without either tail or envelope ; and in a subsequent part of his announcement be adds : the sequel has shown that my surmises were well founded, this proving to be the comet we have lately observed.' This announcement was published in the succeeding volume of the Society's transactions ; but in the mean time Maskelyne, the English astronomer, announced the discovery to M. Messier, and the astronomers of Paris were at once engaged in observing the supposed comet, and in calculating its orbit. Nor were they long in detecting the error that had been committed, in regard to the body in question. On the 8th of May, 1781, less than two months from the first discovery of Uranus as a moving body, Jean-Baptiste-Gaspar Bochart de Saron ascertained that it was much more elongated from the sun than any of the other planets ; and his extraordinary facility, in calculating cometary orbits, had thus early enabled him to know that the motions of this body answered not to a parabolic curve. the first idea of a circular orbit, and this suggestion was carried out, and the orbit determined, by his co-laborer, Méchain, according to the method of Laplace. Thus, through the combined agency of a most happy piece of unexpected good fortune, on the part of Herschel, in England, and the industry and mathematical skill of the Paris astronomers, a new planet stood revealed to the knowledge of mankind, belonging to our own solar family, and yet revolving in an orbit so immensely distant as to envelop all the others, and to give to the known limits of the solar system an augmentation of dimensions almost beyond conception.
It has often been averred - and it is necessary here to repeat the correction, because the errors in question are still found in the newest books — that Dr. Herschel discovered motion in Uranus through the agency of his noted forty feet telescope; and also that he recognised that body as a planet. For the promulgation of the former of these errors, we may refer, among others equally respectable, to a no less authority than Arnott's Elements of Physics, and for the latter, among others, to the North American Review, not to enumerate a multitude of minor publications, many of them school books, and hence in the hands of most of our youth, which has given them currency until they have well.nigh passed into proverbs. Advertence to this subject was called for here, as the only means of justifying some of the above statements; and the expose is equally demanded in justice to the memory of Dr. Herschel himself, who certainly, in his publications upon these subjects, has given no authority for these creations of some unknown pen.
That research might be stimulated, the French Academy of Sciences proposed the theory of the new planet for the subject of the prize of 1790; and although but eight years had transpired, since investigations began, Delambre, produced tables of Uranus which took the prize; and which are found so accurate as to be still retained.
it was disclosed that Uranus revolves in an orbit whose distance from the sun is more than nineteen times as great as that of the earth; and more than twice as great as that of Saturn - the most distant planet known, before this discovery. In this orbit Uranus accomplishes its siderial revolution in a little more than eightyfour years and twenty-nine days - moving like the other planets from west to east. Less than three quarters of a single solar year of that planet, then, has transpired since its first discovery as a member of our solar family! Its apparent diameter is about 4"; yet its real diameter is about thirty-five thousand miles, and its bulk about eighty times that of our earth. Though of such magnitude, yet at the enormous distance at which it is placed, and considering the lentitude of its apparent motion, we can scarcely be surprised that its real character escaped detection so long. The inclination of its orbit to the plane of the ecliptic is less than that of any other planet, being not quite 47'. Dr. Herschel says, “the flattening of the poles of this planet seems to be sufficiently ascertained, by many observations. The seven feet, the ten feet, and the twenty feet instrument equally confirm it;' and hence this planet, it has been inferred, has a motion upon its axis; which, reasoning from analogy, is certainly probable in the highest degree, although the fact has not yet been verified by observation. When its planetary character was detected, fifty-s
7-seven years since, this body was in the constellation Gemini : it is now near 1 of Aquarius, about 89 almost due north from the star Scheat, of the same constellation.
The number of satellites belonging to Uranus is not settled ; but those which are well known offer some peculiarities forming exceptions to rules that have been observed by nature in all other parts of the celestial mechanism with which we have become acquainted. It was not until 1787 that Uranus was known to be attended by
On the 11th of January, of that year, Herschel believed he covered two; and subsequent observations left no doubt of this fact. This discovery was made with his twenty feet reflector, after it had been transformed from the Newtonian form to a front view instrument. Of his great telescope, of forty feet, he says he had his first view in it on the 19th of February, 1787, but that it was not finally completed until the 28th of August, 1789. He afterwards supposed he had discovered four other satellites, and two rings, belonging to this planet; but he subsequently disproved the existence of these last, retaining only the four additional satellites. These have never been seen by any other astronomer, nor has any proof, additional to the opinion of Herschel, been obtained, that there are such bodies. The suspected rings were evidently optical illusions; and it is highly probable that they arose from the defect of figure of the speculum of the forty feet telescope. Indeed this instrument, which has been so often and so constantly the theme of eulogy and admiration, seems never to have been of very extensive
practical use. The figure of the speculum is well known to have been so defective, that the images of the celestial bodies which it produced were distorted, and although very high magnifying powers
upon it, yet the Rev. W. Pearson, a member of the Royal Society, does not hesitate to state, in his “ Practical Astronomy," (4to. London, 1829,) that owing to this defect the magnifying powers used upon it seldom exceeded 200. The belief in its limited usefulness is still farther, and very strongly confirmed, by the fact that this telescope was taken down, some years since, and laid aside, for no other avowed reason except that the frame work had become decayed !
All, then, which is known with certainty respecting the attendants of Uranus, is that it has two satellites ; but these present phenomena wholly unknown in any other portion of the celestial mechanism. . Contrary to the unbroken analogy of the whole planetary systemwhether of primaries or secondaries—the planes of their orbits are nearly perpendicular to the ecliptic, being inclined no less than 780 58' to that plane, and in these orbits their motions are retrograde; that is to say, their positions, when projected on the ecliptic, instead of advancing from west to east, round the centre of their primary, as is the case with every other planet and satellite, move in the opposite direction.'
For these peculiarities no satisfactory cause has been assigned ; and they leave us no less strikingly impressed with the peculiarity of the appendages of the most distant planet now, than we were with those of Saturn, when that was supposed to move upon the utmost border of the solar system. But of the limits of that system, whatever may once have been thought, we can now form no settled opinion. The space beyond the orbit of Uranus, within which the attraction of our sun surpasses that of the sun of any other system, is shown, by the orbits of some comets, to be almost beyond our conception ; nor have we any evidence that these bodies, in their * protracted journeys of a thousand years,' do or do not reach the confines of that space. Certain it is, that space enough is there to allow of a farther augmentation of the number of our primary planets; but whether we shall ever recognise them, if such there are, cannot now be known.
The remarkable, yet wholly empirical law of Bode, touching the distances of the planetary orbits from the sun a law which is also found applicable to the distances of satellites from their primaries if continued beyond Uranus, would give the next planet a distance three hundred and eighty-eight times greater from the sun than the earth, and a siderial revolution of about two hundred and forty-three years. As no fixed proportion between the size and the distances from the sun, is found to prevail among the planets, a body, so far as we know, may hereafter become known to us, even at that prodigious elongation, by reason of great size, aided by improved telescopes, and perhaps, also, by some happy fortuity, such as that which first fixed attention upon Uranus, and one or more of the telescopic planets.
Indeed we cannot aver, with any certainty, that the first observations are not already made and recorded, that are to eventuate in perfecting the discovery of one or more such bodies. Mr. Wartman, of Geneva, observed, in September, 1831, a small star which had an appreciable motion, both in right ascension and in declination ; and in May, 1835, Mr. Cacciatore, of Palermo, observed another (for their positions showed them not the same) distinguished for like motions. In the case of the latter body, calculations, based upon the imperfect observations obtained, render it probable that its orbit, if this be a planet, is at near the same distance from the sun as that of Vesta; but of the star observed by Mr. Wartman, no such approximate determination was obtained. Neither of these bodies, we believe, has ever been seen since the year in which it was discovered ; and what they are, or where arranged, in the celestial economy, if ever made known to us, is still to be disclosed by the future.
R. W. H. Buffalo, June, 1838.
By the deep forest's yet unwaken'd green,
To tread on wither'd leaves, and herbage new,
The downy liverwort's sweet eye of blue,
Amidst the ferns that fringe her mossy brink,
Invites the wanderer to stoop and drink:
The vernal, stirring breeze, and rous'd-up floods !
Raiseth the heart, and the adoring eye,
The slender service-tree that waves so high,
All living things the winter-storm hath left:
Each tinge of life within the rock's dark cleft:
Amidst the shrub-roots, and the old gray stone;
And shadows of the forest branches, lone,
Upward with the elastic air, and scent
Amidst the boughs; and song of waters, blent
Hath worn our nature; and hath lov'd to pray
Gave a religious color to the day;