صور الصفحة
PDF
النشر الإلكتروني

about 101,000 feet per second, the orbit would be circular; its actual velocity, when nearest the sun, is 102,300 feet per second, by reason of which, it is constrained to move in an ellipse; were the projectile force increased to 144,700 feet, the earth's path would be parabolic, and should this intensity be at all augmented, the orbit would be hyperbolic. There can be but little doubt that an ellipse is the figure of the paths of comets as well as of those of planets ; discoveries of recent date confirm the supposition; we know of no heavenly body that moves in a perfect circle, and if the motion were in a parabolic or hyperbolic curve, when once the comet had passed its perihelion, it would continue to recede from the sun, and never return again,—this is evident from the nature of these sections of a cone; but elliptic orbits return into themselves, and the re-appearance of the Encke comet, in the very places predicted, is a proof that this is the curve in which these bodies move. It is usual, however, with astronomers, to calculate the orbit of a comet on the parabolic scheme, which very well represents the motions of a comet, during the time it is visible, though it leaves uncertain the length of the major axis of the ellipse, and, consequently, the period it occupies in revolving round the sun.

The elements of the orbit of a comet are six :

1st. The peribelion distance. 2nd. The situation of the perihelion. 3rd. The place of the nodes. 4th. The inclination of the orbit to the ecliptic. 5th. The time of the perihelion passage. And 6th. The period of the comet's revolution.

Respecting the last particular—the periodic time of a comet-an error, of only a few seconds, will cause a

difference of many hundred years. Some astronomers, in calculating the orbit of the great comet of 1680, have found the length of its greater axis 426 times the earth's distance from the sun, and, consequently, its period 8792 years; whilst others estimate the greater axis 430 times the earth's distance, which alters the period to 8916 years. The celebrated astronomers, Newton and Halley, judged that this comet completed a revolution in 575 years. A similar disagreement exists respecting the comet of 1811, as determined by different astronomers, its period was, according to Calandrelli, 3056 years ; Bessel, 3383 years; Lemaur, 4237 years; Ferrer, 3757

years.

Beneath thine all-directing nod,
Both worlds and worms are equal, God!
Thy hand the Comet's orbit drew,
And lighted yonder glow-worm too;
Thou didst the dome of heaven build up,
And spreadst yon cowslip’s glittering cup.

[graphic][ocr errors]

A TABLE

OF THE SUN'S RISING AND SETTING, RIGHT ASCENSION,

DECLINATION, AND EQUATION OF TIME.

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

A TABLE

OF THE
TRANSITS OF THE MOON AND PLANETS.

Day. Moon. Mercury. Venus. Mars. Jupiter. Saturn. Uranus.

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

SEPTEMBER.

O azure vaults! O crystal sky!

The world's transparent canopy,
Break your long silence, and let mortals know
With what contempt ye look on things below.

Great eye of all, whose glorious ray

Rules the bright empire of the day,
O praise his name, without whose purer light
Thou hadst been hid in an abyss of night.

Ye moon and planets, who dispense

By God's command your influence,
Resign to him, as your Creator, due
That veneration which men pay to you.

Fairest as well as first of things

From whom all joy, all beauty springs,
O praise th’ Almighty ruler of the globe,
Who useth thee for his imperial robe.

Praise Him, ye loud harmonious spheres,

Whose sacred stamp all nature bears,
Who did all forms from the wide chaos draw,
And whose command is th’universal law.

Wentworth Dillon, Earl of Roscommon.

SOLAR PHENOMENA. The autumnal equinox arrives, and the sun enters Libra at 39 min. after 1 of the morning of the 23rd of this month.

The earth, in its circle round the sun, attaivs that point of its course wherein every part of its surface, from pole to pole, receives an equal proportion of the solar influence. After this period, the arctic regions will gradually sink into the darkening gloom of their long and dreary night; and the northern nations of the globe have, in sure succession, the misty morn, the fleeting cloud, the moaning gale, the ice-bound stream, and the snowy mantle of winter. The sun, verging towards the south, will daily contract his course and diminish his meridian height—his rising and setting occasionally diversified with a splendor peculiar to the autumnal season. During the long absence of the sun, the atmosphere, refined by frost, will reveal the beautiful and unimaginable depths of ether, glowing with myriad stars, and those mysterious phenomena which lie far beyond, where the stars of Orion, and their bright companions, send forth their keen scintillations.

LUNAR PHENOMENA.

Phases of the Moon.
First Quarter, 2nd day at 30 min. after 1 morning.
Full Moon, 10th .... 33 ........ 5
Last Quarter, 17th .... 45 ........ 1 afternoon.

New Moon, 24th .... 8 ........ 7 morning. Conjunctions of the Moon with the Planets and Stars. September 4th, with o in Sagittarius. . at 8 evening.

7th, .... Uranus .......... 2 afternoon. 10th, .... Jupiter ........... 5 13th, .... 2 & in Cetus ......11 night. 15th, .... Mars .............10 18th, .... vin Gemini ...... 7 morning. 22nd, .... Mercury .......... 10 night. 23rd, .... Saturn ............11 morning. 25th, .... Venus ............10

« السابقةمتابعة »