Imágenes de página
PDF
ePub

the microscope, as I have shewn in my Essays on that instrument.

The Georgium Sidus was discovered by Dr. Herschel, in the year 1781: for this discovery he obtained from the Royal Society the honorary recompence of Sir Godfrey Copley's medal. He named the planet in honour of his Majesty King George III. the Patron of science, who has taken Dr. Herschel under his patronage, and granted him an annual salary. By this munificence he has given scope to a very uncommon genius, and enabled him to prosecute his favourite studies with unremitted ardour.

In so recent a discovery of a planet so distant, many particulars cannot be expected. Its year is supposed to be more than 80 siderial years; its diameter 34,299 miles; the inclination of its orbit 43' 35'; its diameter, compared to that of the earth, as 431,769 to 1; in bulk it is 8,049,256 times as large as the earth. Its light is of a bluish white colour, and its brilliancy between that of the Moon and Venus.

Though the Georgium Sidus was not known as a planet till the time of Dr. Herschel, yet there are many reasons to suppose it had been seen before, but had been considered as a fixed star. Dr. Herschel's attention was first engaged by the steadiness of its light; this induced him to apply higher magnifying powers to his telescope, which increased the diameter of it: in two days he observed that its place was changed; he then concluded it was a comet; but in a little time Dr. Maskelyne, himself, and others, determined that it was a planet, from its vicinity to

the ecliptic, the direction of its motion, being stationary in the time, and in such circumstances as to correspond with similar appearances in other planets.

With a telescope, which magnifies about 300 times, it appears to have a very well-defined visible disc; but with instruments of a smaller power it can hardly be distinguished from a fixed star, between the sixth and seventh magnitude. When the moon is absent, it may be seen by the naked eye.

Dr. Herschel has since discovered that it is attended by six satellites: a discovery which gave him considerable pleasure, as the little secondary planets seemed to give a dignity to the primary one, and raise it into a more conspicuous situation among the great bodies of our solar system.

As the distances of the planets, when marked in miles, are a burthen to the memory, astronomers often express their mean distances in a shorter way, by supposing the distance of the earth from the sun to be divided into ten parts. Mercury may then be estimated at four of such parts from the sun, Venus at seven, the Earth at ten, Mars at fifteen, Jupiter at fifty-two such parts, Saturn at ninety-five, and the Georgium Sidus 190 parts.

By comparing the periods of the planets, or the time they take to finish their revolutions, with their distance from the sun, they are found to observe a wonderful harmony and proportion to each other; for the nearer any planet is to the sun, the sooner does he finish his revolution. And in this there is a

constant and immutable law, which all the bodies of the universe inviolably observe in their circulations; namely, That the squares of their periodical times are as the cubes of their distances from the centre of the orbit, about which they regularly perform their motions. We are indebted to the sagacity of Kepler for the discovery of this law; he was indeed one of the first founders of modern astronomy.

I cannot conclude this general survey of the solar system better than in the words of that excellent mathematician, Mr. Maclaurin. "The view of nature, which is the immediate object of sense, is very imperfect, and of small extent; but, by the assistance of art, and the aid of reason, becomes enlarged, till it loses itself in infinity. As magnitude of every sort, abstractedly considered, is capable of being increased to infinity, and is also divisible without end; so we find that, in nature, the limits of the greatest and least dimensions of things, are actually placed at an immense distance from each other.

"We can perceive no bounds of the vast expanse, in which natural causes operate, and fix no limit, or termination, to the universe. The objects we commonly call great, vanish, when we contemplate the vast body of the earth. The terraqueous globe itself is lost in the solar system; the sun itself dwindles into a star; Saturn's vast orbit, and all the orbits of the comets, crowd into a point, when viewed from numberless places between the earth and the nearest fixed stars. Other suns kindle to illuminate other systems, where our sun's rays are unperceived; but

they also are swallowed up in the vast expanse. When we have risen so high, as to leave all definite measures far behind us, we find ourselves no nearer to a term or limit..

"Our views of nature, however imperfect, serve to represent to us, in a most sensible manner, that mighty power which prevails throughout, acting with a force and efficacy that suffers no diminution from the greatest distances of space, or intervals of time; and to prove that all things are ordered by . infinite wisdom and perfect goodness; scenes which should excite and animate us to correspond with the general harmony of nature."

ACCOUNT OF THE DISCOVERY OF THE FOUR NEW NAMED CERES, PALLAS, JUNO, AND

PLANETS
VESTA*.

Professor Piazzi, of the university of Palermo, in Italy, a very able astronomer, discovered on the first of January, 1801, a moveable star which had the appearance of a new planet; he estimated its bulk to be about 1 that of the earth; and its position in our system to be between Mars and Jupiter. In compliment to the present sovereign, the founder of the Palermo observatory, he denominated it Ceres Ferdinandia; and it is now generally called Ceres. Subsequent observations on this planetary body made by Dr. Maskelyne, Dr. Herschel, and other

* I have availed mys: If of the opportunity, in the present edi tion, of inserting the above discoveries.-EDIT.

astronomers of this country, France, and Germany, appear at present to confirm its identity with the other planets. On the 4th of February, 1802, Dr. Maskelyne at the Royal Observatory, Greenwich, observed this planet passing the meridian, between 3 and 4 o'clock in the morning, having about 188* 43′ right ascension, and 12' 38′ north declination, in appearance like a star of the 8th magnitude; and preceding the 11th of the same month, he had sufficiently observed it, so as fully to ascertain its motion. With a power of 60, it appeared to have a visible disc, when on the meridian; and through a clear air, the disc was round and well defined, and rather smaller than that of the 34th of Virgo, an approximate star of the 6th magnitude; at the same time Dr. Maskelyne remarked that the smallness and rotundity of the appearance of the fixed stars is a good criterion of the clearness of the air. The light of this planet is of a reddish hue, and has been judged to resemble that of the planet Mars. From the earth's position and quicker motion in its orbit, it appeared stationary on the 6th and 7th of February last, and has had since an apparent retrograde motion. Dr. Herschel judges it to be not larger than a fourth part of the diameter of the Georgium Sidus, and its apparent diameter 22". This planet was in opposition to the sun on March 17, 1802. Therefore, at this time, October 6th, its proximity to the sun, and twilight, prevents any observation. In the month of January next, observations of it may be re-assumed. Baron De Zuch's computation of its place for April

« AnteriorContinuar »