Jupiter is the largest planet of the system, and when in and near opposition shines with a brilliancy inferior only to Venus. A friend of the writer has informed him that on October 16, 1857, the planet's lustre was so considerable as to throw a sensible shadow. When telescopically examined, the surface of Jupiter is found to be marked with a series of dusky streaks, commonly known as the “ belts.” These belts vary greatly in form, size, and number from time to time. Occasionally only two or three broad ones are seen, at other times as many as eight, ten, or even a dozen narrow ones. Their physical nature is not well understood, but they are usually considered to be masses of cloud, acted upon in a manner in some way analogous to our terrestrial trade-winds, If this is the true hypothesis, as probably it is, then the planet has wind, rain, water and clouds, and is consequently fitted for the existence of animal and vegetable life. The existence of the belts was first detected by Zuppi, at Naples, in May 1730, though a claim has been put in on behalf of Torricelli.

Aberration. — The aberration of light is another important phenomenon which requires to be taken into consideration in the reduction of rough astronomical observations. Although light travels with the enormous velocity of 192,000 miles per second—a speed so great, that for all practical terrestrial purposes we may consider it to be propagated instantaneously; yet the astronomer, who has to deal with distances of millions of miles, is obliged to be more particular. A simple illustration will show this: the mean distance of our globe from the Sun is 95,000,000 of miles, and since light travels at the rate of 192,000 miles, we can ascertain by a simple arithmetical process that the time occupied by a ray of light reaching us from the Sun is 8m. 18s., so that in point of fact, in looking at the Sun at a given moment, we do not see it shining as it is, but as it did 8m. 18s. previously. If the Earth were at rest, this would be all very well; but since the Earth is in motion, when the solar ray enters the eye of a person on its surface, he will be some way removed from the point in space at which he was situated when the ray left the Sun; he will consequently see that luminary behind the true place it actually occupies when the ray enters his eye.

When an inferior planet is in superior conjunction, and “has a latitude or distance from the ecliptic less than the Sun's semi-diameter, it will be less distant from the Sun's centre than such semi-diameter, and will therefore be within the Sun's disc. In this case, the planet being between the Earth and the Sun, its dark hemisphere being turned towards the Earth, it will appear projected upon the Sun's disc as an intensely black round spot. The apparent motion of the planet being retrograde, it will appear to move across the disc of the Sun from east to west, in a line sensibly parallel to the ecliptic.” Such a phenomenon is called a transit, and as it can only occur in the case of the inferior planets, or those which pass between the Earth and the Sun, it is limited to Vulcan, Mercury, and Venus. The observations of these planets are used in a manner which we cannot here explain, for the purpose of ascertaining the distance of the Earth from the Sun.

James Gregory (inventor of the reflecting telescope which bears his name) seems to have been the first to point out this application of transit observations.

When any celestial object is concealed by the interposition of another, it is said to be occulted, and the phenomenon is called an occultation. Strictly speaking, an eclipse of the Sun is an occultation of that luminary by the Moon, but usage has given to it the exceptional name of “ eclipse.” The most important phenomena of this kind are the occultations of the planets and larger stars by the Moon, but the occultation of one planet by another, on account of the rarity of such an occurrence is exceedingly interesting. Inasmuch as the Moon's apparent diameter is about ½°, it follows that all stars and planets situated in a zone extending ¼° on each side of her path, will necessarily be occulted during her monthly course through the ecliptic. The great brilliancy of the Moon entirely overpowers the smaller stars, but the disappearance of the more conspicuous ones are visible in a telescope, a table of which is inserted every year in the Nautical Almanac.

It must be remembered, that the disappearance always takes place at that limb of the Moon which is presented in the direction of its motion.

In this chapter we shall briefly advert to a few historical remarks, relating to cometary astronomy.

Going back to the early ages of the world, we find that the Chaldæans considered comets to be permanent bodies analogous to planets, but revolving round the Sun in orbits so much more extensive, that they were therefore only visible when near the Earth. This opinion, which, by the by, is the earliest information we have of there being periodical comets, was also held by the Pythagorean school of philosophers. Yet Aristotle, who records this, insists that comets are merely mundane exhalations, carried up into the atmosphere, and there ignited.

Anaxagoras, Apollonius, Democritus, and Zeno considered that these bodies were formed by the clustering of many smaller planets.

It is a somewhat remarkable fact, that Ptolemy, so celebrated for his varied astronomical attainments, should nowhere have made any mention of comets; his omission is, however, made up for, by Pliny, who seems to have paid much attention to them. He enumerates 12 kinds, each class deriving its name from some physical peculiarity of the objects belonging to it.

A total eclipse of the Sun is a most imposing spectacle, especially when viewed from the summit of a lofty mountain. Words can but inadequately describe the grandeur and magnificence of the scene. On all sides, indications are afforded that something unusual is taking place. At the moment of totality the darkness is sometimes so intense that the brighter stars and planets are seen, birds go to roost, flowers close, and the face of nature assumes an unearthly cadaverous hue; not the least striking thing is the sudden and frequently considerable fall that takes place in the temperature of the atmosphere, as the time of the greatest obscuration draws near.

Although to the unaided eye all the stars appear single, yet in numerous instances the application of suitable optical assistance shows that many consist in reality of two stars, placed in juxtaposition so close together that they appear as one. These are termed double stars. Only 4 of these objects were known, until Sir W. Herschel, by means of the powerful telescopes constructed by himself, discovered a large number never before suspected. He observed and catalogued, altogether, about 500, which subsequent observers, especially P. G. W. Struve, and Sir J. Herschel, have augmented to near 6000.

The following have been selected by Sir J. Herschel from Struve's catalogue, as remarkable examples of each class, well adapted for observation by amateurs, who may be disposed to try by them the efficiency of telescopes.

If two stars lie very nearly in the same line of vision, whatever may be their distances, they will form an optical double star, or one whose components are only apparently, but not really joined together. Herschel, considering it extremely unlikely that this was the case, undertook, in 1778, carefully to investigate the subject.

This is a subject on which we have a few words to say. In the early days of this branch of astronomical discovery, a sort of understanding was come to by astronomers that the names given to these bodies should as far as possible be those of ancient female divinities. So much for the theory which is unexceptionable. Now for the practice. This is bad in two ways: — 1. The original arrangement is constantly broken through; and 2, sufficient precautions are not taken to choose names, which cannot be mistaken (by reason of similarity of sound) for ones, previously appropriated. With reference to the 1st, we havo nothing particular to say against such names as Parthenope, Massilia, Isis, &c., as they indicate where the discovery wts made, but we most emphatically protest against the fawning servility which prompted such appellations as Eugenia, and Maximiliana, and Angelina. We have the highest opinion of the excellence of the Empress of France, nor do we doubt that King Maximilian of Bavaria has deserved well of his German subjects, but why should they be raised to the skies? In 1813 the Academy of Leipzic proposed to add the name of Napoleon I. to the constellations; astronomers, with much good sense, repudiated the idea. Has the race degenerated? The same remarks apply with equal force to Angelina.

Nature, though she lias supplied us with, visible phenomena to measure the larger units of time, such as days, months, and years, has not furnished us with any means whereby we may measure the lesser units of hours, minutes and seconds; artificial contrivances must therefore be sought for. Hough approximations to the true time were at first obtained by setting up gnomons, or upright staves; which, in conjunction with a knowledge of the north point of heavens, would afford a tolerably correct indication of noon, or the moment of the Sun's passage over the meridian. An instrument constructed with a gnomon pointing towards the North Pole of the heavens, constitutes a sun-dial, and affords a still better mode of ascertaining the hour of the day. According to Herodotus, sun-dials were first introduced into Greece from Chaldæa; the hemisphere of Berosus, who lived 540 B.C., is the oldest recorded in history. The earliest attempt to form a strictly artificial time-keeper, is due to Ctesibius, of Alexandria, who invented Clepsydrœ, or water-clocks, which were contrivances for allowing a continuous stream of water to trickle through a small aperture in the pipe of a funnel, the time being measured by the quantity of fluid discharged.

The phenomena, of which we are now about to speak, form a highly interesting and by no means unimportant branch of descriptive astronomy. We shall treat of the subject under three heads: —

1. Aërolites.

2. Fireballs.

3. Shooting Stars.

Of all cosmical meteors, those known as aërolites, meteorlites, or meteoric stones, are the rarest, but nevertheless not so rare as to prevent the most satisfactory evidence being given, that such occurrences have happened from time to time. It is to Chaldni that we owe much of our knowledge on this branch of the subject. Many of these meteoric stones, picked up in different parts of the world, have been subjected to chemical analysis at the hands of Berzelius, Eammelsberg, and others, whose deductions may be thus summed up: —

1. Meteoric stones are composed of elements all of which occur in terrestrial minerals.

2. Of the 65 elementary substances known, 19 have been found in meteoric stones.

3. The produce of a meteoric shower may be divided into meteoric iron and meteoric stone.

4. Meteoric iron is an alloy that has not been found among terrestrial minerals, and is composed of about 10 per cent, of nickel with small quantities of cobalt, manganese, magnesia, tin, copper, and carbon.

5. […]

There are many stars which exhibit periodic changes of brilliancy quite unaccounted for by any causes with which we are acquainted; these are termed variable stars. One of the most remarkable is o Ceti (Mira), which was first observed by David Fabricius in 1596. It appears about 12 times in 11 years; remains at its greatest brightness about a fortnight, when it sometimes equals in brilliancy a star of the 2nd magnitude; decreases during about 3 months till it becomes totally invisible; it remains so for about 5 months, and then gradually recovers its brilliancy during the remaining 3 months of its period. Its maximum brightness is not always the same, nor does it always increase or diminish by the same gradations. According to Hevelius, nothing was seen of it between October, 1672, and December, 1676. Algol (β Persei) is another well-known instance of this kind. For about 2d. 13h. it shines as an ordinary star of the 2nd magnitude. In about 3½ hours it is reduced to the 4th magnitude, and thus remains about 20 minutes; it then rapidly increases to the 2nd, and continues so for another period of 2d. 23h., when similar changes recur.

A new comet having been discovered, the first thing an astronomer does, is to obtain 3 observations of it, whereby he may compute the elements of the orbit. He then examines a catalogue of comets, to see if he can identify the newly-found stranger with any that have been before observed. The value of a complete catalogue is therefore obvious, and as nothing of the kind has, as far as we are aware, been published for some years, we have been led to compile a new one.

In the preparation of the following, care has been taken that only the most reliable orbits that were to be obtained should be inserted, the general rule being to prefer the one which was derived from the longest arc, other things being satisfactory. Among the authorities consulted may be mentioned Pingré, Hussey, Olbers, Cooper, Hind, Arago, and others.

Owing to its proximity to the Sun, observations of the physical appearance of this planet are obtained with difficulty, and even then are liable to much uncertainty. Schröter, who paid considerable attention to Mercury, thought he had detected traces of the existence of high mountains on its surface; his observations, however, were not confirmed by Sir W. Herschel. Mercury exhibits phases similar to those of the Moon. At its maximum elongations, only half its disc is illuminated, but as it approaches its superior conjunction, the breadth of the illuminated part increases, and its form becomes gibbous, and ultimately circular in conjunction, when, however, the planet is lost in the Sun's rays and invisible; on emerging, the gibbous form is still preserved, but the gibbosity is on the opposite side. The breadth of the illuminated part diminishes as the planet draws near its greatest elongation, when it again appears like a half moon, and continues to become more and more crescented as it approaches the inferior conjunction; having passed this, the crescent (now on the opposite side) gradually increases until the planet again reaches its greatest elongation.