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SOUTHEY.

You set too great and exclusive a value on things seen and temporal; but I'm not going to be dogmatical with you. For my part, my very happiest moments are those when I am anticipating that future life where change shall be ever for the better, and progress shall be without decay, and happiness without evanescence.

rest.

dove, that I might flee away and be at tell. This is a sorry confession to make; but I will not ape a spiritual sublimity which I do not feel.

LAMB.

Whereas I cling to this present state of being, with a tenacity that becomes deeper and firmer with every furrow in the soil of my heart. I shrink from the thought of new and untried existence. I would never leave familiar faces and familiar scenes. Thoughts of an expanded and elevated sphere, instead of consoling, depress me more than I can

From Hogg's Instructor.

COMETS.

IN the ages of ignorance and superstition, very wild and extraordinary opinions have been entertained regarding the nature of comets, and the purposes for which they appear in the heavens. The ancient Chaldeans, and Pythagoras, with some of his followers, believed them to be of the nature of the planets. Aristotle supposed them to be meteors in the upper heavens, generated when they appeared, and vanishing out of sight by being destroyed. In later times, Kepler, noted for the wildness of his imagination, as well as for the strength of his genius, fancied comets to be monstrous and uncommon animals generated in the celestial spaces. Bodin, a French writer of the sixteenth century, maintained that comets "are spirits, or geni different from men, yet mortal, which, having lived on the earth innumerable ages, and being at length arrived on the confines of death, celebrate their last triumph, or are recalled to the firmament, like shining stars." An opinion something like this, extravagant though it be, prevailed in remote ages; for we find that the people generally believed that a great comet which appeared immediately after the assassination of Julius Caesar, was the soul of that celebrated man. The conjecture for all was yet only conjectureof Bernoulli, an Italian philosopher, was nearer the truth, and yet far from it: He thought that comets were the satellites of some far-off planet, invisible on account of its distance, which wander betimes within the sphere of our vision.

Sir Isaac Newton believed that the orbit of the comet of 1680 would become gradually less, and that at last the comet would fall into the sun; thus, in his opinion, fulfilling one of the uses of comets, namely, to furnish fuel for the sun, which was supposed to be necessary, to prevent the sun from being wasted away by giving out so much light. Mr. Brydone seemed to hold the same opinion with regard to almost all the comets without tails, which he alleges are seen approaching the sun, but of whose return from the sun no evidence satisfactory to him was ever given. Such were the opinions of philosophers regarding comets, before the accurate observations, superior instruments, and profound calculation of modern science made us better acquainted with them.

Whilst the learned formed conjectures regarding comets that were wide of the truth, ignorance and superstition invested them with a mysterious and awful significance. They were regarded as omens or forerunners of war, or pestilence, or famine; of the birth of mortals who were to be great for good or evil among their fellows; or of those calamities which too often followed the death of the great conquerors of antiquity. Princes, popes, peoples, were perplexed and alarmed by the appearance of these strange wanderers in the heavens, as they glared down in their fiery splendor, or gave forth their pale, livid, watery light, the very emblem, as men thought, of plague and famine; or as their

immense trains swept across the heavens, | greater or less condensation.
attracting every eye, and filling men's hearts
with astonishment and anxiety.

Speaking of Mithridates the Great, king of Pontus, the historian Justin says, "The celestial signs had foretold the future greatness of this man. For, in that year in which he was born, and in that in which he first began to reign, the star of a comet, through each time, so shone for seventy days, that all the heaven seemed to be in a blaze. For it had taken up the fourth part of the heaven by the greatness of it, and had overcome the brightness of the sun by the splendor of it; and it occupied the space of four hours in rising and setting." A comet which appear ed in 837 so alarmed the reigning king of France, Louis I., that he ordered a number of churches and monasteries to be built throughout his dominions, in the hope that thereby he would appease the wrath of Heaven, of which he supposed the comet to be an indication. And in 1446, the pope of that day, Calixtus III., hard pressed by the successes of the Turks under Mahomet II., was greatly alarmed by the appearance of a remarkable comet, and he appointed a form of prayer to be used against its supposed baleful influence; and, for the same end, he ordered the bells in all the churches to be rung every day at noon. But, "Thus saith the Lord, be not dismayed at the signs of heaven, for the heathen are dismayed at them."

Though much has yet to be learned regarding comets, the observations and labors of modern science have led to a good deal of trustworthy knowledge of them, and have shown them to be very harmless, but very interesting celestial phenomena. In this paper we shall attempt to give a rapid sketch of what is known regarding comets, and espe cially of the results of recent investigations, drawing our materials chiefly from the work of Mr. Hind.

Some comets are distinctly, and even conspicuously visible to the naked eye; others (and these by far the greater number) are only to be seen by the aid of the telescope. In almost every instance in which they are conspicuously visible to the naked eye, comets consist of a head composed of a nucleus of light surrounded by a mass of nebulous matter, and of a tail or train of nebulous light stretching out from the head or nucleus. When we direct the eye or the instrument to the head of a comet, we see sometimes a star-like body in the centre, sometimes a disc-like appearance, and sometimes evidently only the nebulous matter, in a state of

VOL. XXXIV.-NO. III.

The celebrated French philosopher Arago was of opinion that some comets are solid bodies like the planets; and he rested that opinion very much on an alleged fact, that a comet has been observed as a round black spot on the body of the sun, in its transit across the disc of that luminary, like the planets Mercury and Venus in similar circumstances. There is the strongest reason to believe, however, that what have sometimes been taken for opaque or planetary nuclei, were nothing but the nebulous or gaseous matter of which comets are composed, in a very high state of condensation. It having been computed that the comet of 1827 would cross the sun's disc, the occurrence was looked forward to with much interest, as fitted to furnish the best information regarding the nuclei of comets. Unfortunately, the sun at the computed time was hidden by clouds in this country; he was seen, however, by the French observers at Verviers and Marseilles; but no spot or cloud could be discovered on the sun's disc; and hence it was concluded that the comet had no solid or opaque part whatever. Besides, when comets have presented to the observer what seemed to be a solid planetary disc, it has been found that the appearance of that disc underwent changes of shape and character altogether inconsistent with the fact of it being a solid substance. And it is held to be doubtful whether a single instance can be produced of a comet with a planetary disc presenting the same appearance throughout the whole period that it was observed. Indeed, the changes exhibited by the central portion of the heads of cometsin other words, the different appearances presented by the disc, in those of them which are so furnished-are among the most puzzling of the phenomena connected with these bodies.

The nuclei of different comets present very different appearances, and even the nucleus of the same comet evidently undergoes, as we have just stated, great and surprising changes. A remarkable comet appeared A. D. 389, whose head seemed composed of several small stars. The nucleus of the comet of 1835-36, usually called Halley's comet, presented at one time the appearance of a fanshaped flame, proceeding from a bright point: at another time, it was like a red-hot coal of an oblong form; at another time, it was seen as a well-defined disc, with an apparent diameter of not less than 97,000 miles; and at another time, as a brilliant kernel of light, with a diameter varying from 250 to 1,000

24

miles. The comet of 1807 was seen by Sir W. Herschel to have a well-defined planetary disc of a circular form. Sir William also saw a similar planetary disc in the head of the great comet of 1811; but, when that comet was examined by glasses of high power, the appearance of the stellar nucleus vanished. In 1819 a comet was observed, which exhibited phases similar to those of a crescent moon, during a part of the time that it was visible. The nucleus of a comet which ap peared in 1825, as seen by Professor Santini, appeared to be composed of three bright spots. The great comet of 1843 had at one time a nucleus, small, but extremely bright; at another time it exhibited a well-defined planetary disc.

The different appearances thus presented by the nuclei of different comets, and still more the differences observed in the nucleus of the same comet at different times, seem plainly to indicate that the nuclei of comets are not solid bodies, and that they consist of nebulous or gaseous matter considerably or highly condensed.

Some comets are exceedingly brilliant; so much so, that they have been distinctly visible during the day, and while the sun was shining, and have also cast a shadow at night. This was the case with the comet mentioned by Diodorus Siculus, and also with the one which appeared at the birth of Mithridates, B.C. 134, to which we have already referred. One of the comets of 1618 was distinctly seen in full day light; and an instance occurred, in July, 418, of a comet that had not been observed before, being detected as a bright body in the neighborhood of the sun during an eclipse. The comet of 1744 was observed with the telescope at noon day, and many persons could distinctly see it with the naked eye for a considerable period after sunrise. Two comets of extraordinary brightness appeared in 1402; they were seen day and night, and caused great alarm.

Usually the head in comets exhibits a pale, livid, white light; sometimes it is fiery red; sometimes a dull red, inclining to yellow; and occasionally it presents a greenish, and sometimes a bluish tinge. The comet of 1811 had a disc of a pale ruddy color; the surrounding nebulosity was greenish, or bluish green. The nucleus of the comet of 1843 was of a golden hue, of the color of Venus, or reddish, according to different observers. The comet of 1652 was of a pale livid color. The Chinese describe the comet of 1577 as of a bluish color, with a white vapor.

But it has been chiefly the tails of comets

that have attracted the attention of mankind, and filled them with astonishment, and often, in the days of ignorance and superstition, with terror. The generality of comets visible to the naked eye are tailed comets. The tail is usually developed as the comet approaches the sun; and just after it has passed that body, it for the most part appears to attain its greatest dimensions. In some comets, the tail is an elongated train of light, becoming fainter towards the extremity; in others, it is rounded off, bushy, or fan-shaped. Sometimes the elongated tail seems to be split at the end, so as to present the appearance of two or more tails.

The tail generally projects from the head of the comet in a direction away from the sun, so as to be a continuation of the line drawn from the sun to the head of the comet. This, however, is not always the case: for in the comets of 1577 and 1680 the tail deviated from the line joining the sun and the comet-that of the former 21°, and that of the latter 5°. Sometimes, when comets have two tails, the one is in the usual direction, and the other is towards the sun. The comets of 1824 and 1845 were of this kind; that of 1824 had two tails, making with each other an angle which varied from 138° to 170°; and the two tails of that of 1845 made with one another an angle of about 140°. The tail of the same comet has been observed to vary greatly in appearance, and that sometimes in the course of a single night.

Occasionally a vibratory or coruscating motion, something resembling certain of the motions of the aurora borealis, has been noticed in the tails of some comets. The Chinese, to whom we are indebted for a large number of careful observations of early comets, were the first to notice these vibrations in the tail of a comet which appeared A. D. 615, and they have often been observed since. Longomontanus described the tail of the comet of 1618 as having "an enormous vibration;" another observer says that it appeared as if agitated by the wind. In the great comet of 1843, the pulsations of the tail were distinctly visible.

Some comets have tails not straight, but curved, presenting to the eye of wondering and alarmed nations the appearance of an immense flaming sword hung out in the heavens. Such a phenomenon was held to portend bloody wars.

The apparent and real length of the tail are generally different. If the eye of the observer be in a line drawn through the tail lengthwise, the tail will seem to make a part

tail.

of the head, or, in other words, no tail will atmosphere, which is straightway driven back be distinguishable ; if the eye be a little out by some repelling power, and, passing along of the line, the tail will appear short; and it the sides of the comet, forms the tail. If is only when the eye is in a line at right an- this conjecture be correct, then the repelling gles, or nearly so, to the tail, that the whole power, whether coming from the sun, or length of it will be seen.

whencesoever it comes, must be prodigiously In some comets, the apparent length of great, for the tail generally retains a rectilinthe tail has been enormous, stretching over eal direction away from the sun, whether the 40°, 30°, 60°, and 100° of an arc of the comet be sweeping down in space towards heavens. A comet, observed in the southern that luminary, or be wbirling with lightning hemisphere in 1689, had a tail that extended speed round him in its perihelion, or nearest over 60°, and was two hours and a half in distance to him, or be receding away into rising. And we are told of the great comet space after it has passed him. which appeared in 1264, that, when its head There is considerable difficulty in finding was just above the eastern horizon, the tail the real magnitude of comets, from its being stretched away westward to beyond the mid- impossible to determine precisely where the heavens. The nearer that the comet is to the nebulous matter of which the head is comeye of the observer favorably situated, the posed terminates, inasmuch as it appears to greater will be the apparent length of the thin off from the centre, and gradually to

shade away into darkness. Besides, the But the real length of the train of light nebulous matter evidently contracts and exthat accompanies these wonderful bodies, is pands, so that the same comet has different even more confounding than its apparent dimensions at different periods. Still, the length. The tail of the celebrated comet of measurement of a number of comets ba 1680 was considerably more than 100,000,000 been accomplished, we believe, with considerof miles long; that of the comet of 1744 able accuracy. was 19,000,000 of miles ; that of the comet But, besides the contractions and expanof 1769 about 40,000,000 of miles. The sions which take place in the heads of comets great comet of 1811 had a tail of upwards from causes altogether unknown to us, there of 100,000,000 of miles in length; and the are other contractions and expansions wbich second comet of that year was accompanied some at least of these bodies undergo with by a tail 130,000,000 of miles in length;

whilst considerable regularity, and which apparently the comet of March, 1843, had a train of light depend on their approach to and departure stretching away from the nucleus, or head, from the sun. In approaching the sun they to the astonishing distance of 200,000,000 are observed to contract, in receding from of miles.

the sun they are observed to expand. This There is something in such enormous meas is certainly contrary to what we would exures of distance which the mind can hardly pect, and it is one of the many intimations grasp, that swells out our conceptions of the which we have that the physical constitution wisdom and power of Him who created and of comets--the matter of which they are rules these glorious wanderers. And in con- composed—is something of which we on nection with that wisdom and power, what earth have no experience, and can form no thoughts should we have of the first sleep of conception. the Infant in the manger of the stable at All comets, most probably, move in an elBethlehem, of the agony in the garden, of the lipse, often of very high eccentricity, although ignoming on the cross, of the humiliation and it may be that some of them, from the very helplessness in the tomb which a stranger's great velocity with which they pass their kindness supplied !

perihelion, move in a parabola, or in a hyperIn some comets there is a rim or border bola. Some comets have a direct motion in of light on the head next the sun, and pass. the order of the signs of the zodiac-i. e., in ing round on each side to form the com- the same direction as the earth and the planmencement of the tail. That border is callets; others move in a contrary or retrograde ed the envelope. Of the manner in which direction. Of the 206 comets whose orbits the envelope and tail are formed, astronomers have been calculated down to the end of 1852, can as yet do little more than conjecture. 105 have a direct, and 101 have a retroBut it is supposed that the nucleus, or more grade motion. The paths of comets are not condensed part of the head, being acted confined to the ecliptic, as those of the planupon by the sun, throws off, or outwards ets are, but comets are seen in all parts of toward the sun, a portion of the cometic the heavens-about the poles, as well as in

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the zodiacal regions. They come darting forth towards the sun from every quarter in space, and having wheeled round him with inconceivable rapidity, they rush away back into those "depths profound" whence they emerged.

Of the number of comets we can have no certain knowledge. More than 7,000,000 of these bodies, according to Arago, come within the orbit of Uranus. Mr. Hind supposes that probably somewhat above 5,000 comets have approached the sun within the orbit of Mars; of these there are trustworthy records of rather more than 600.

The discovery that comets move in an ellipse, having the sun in one of the foci, and that they will, therefore, periodically visit the neighborhood of the sun, was one of surpassing interest, and the determination of the periods of their return is one of the greatest triumphs of human intellect. Let us briefly advert to that discovery.

At an early period it was thought that comets moved in straight lines. When this was found to be an error, and they were observed to move in a curve, that curve was supposed to be a parabola, or a hyperbola. And indeed the parabola and hyperbola differ very little from the ellipse in the small part of a comet's orbit, in which it can be observed. For it is only for a comparatively short space before a comet reaches its perihelion, and after it passes it, that it is within the reach of the astronomer's eye or instruments. But it was by-and-by found that the observations made on the orbits of different comets would by no means agree with the supposition that they were moving in a parabola, and plainly indicated that their orbit was an ellipse. The orbits of a number of such comets have been calculated, and the result has been the determination of the periodical times of several comets; and these calculated periodic times have been verified by the return of the comets as predicted. The most celebrated are the comets known by the name of Halley's Encke's, and Biela's comets. A brief notice of these may not be devoid of interest, and may assist us in obtaining a more distinct notion of the cometary world.

Guided by the light which his great theory of gravitation threw on a variety of astronomical observations, Sir Isaac Newton came to the conclusion that the comets, like the planets, revolve round the sun. If this had before been suspected, it had not in any way been proved. To verify it, if really true, became an object of deep interest to Newton, and his

friend Dr. Halley. "At Newton's suggestion," says Mr. Mitchell of Cincinnati, "Halley had searched all ancient and modern records for the purpose of rescuing any historical details touching the appearance and aspects of comets from the primitive ages down to his own time. On the appearance of the comet of 1682, he observed its position with great care, and with wonderful pains computed the elements of its orbit. He found it moving in a plane but little inclined to the ecliptic, and in an ellipse of very great elongation. In its aphelion it receded from the sun to the enormous distance of 3,400,000,000 of miles. He discovered that the nature of its orbit was such as to warrant the belief that the comet would return at regular intervals of about seventy-five years; and, recurring to his historical table of comets, he found it possible to trace it back with certainty several hundred years, and with probability even to the time of the birth of Mithridates, one hundred and thirty years before Christ."

From his computation, and from what he believed to be the historical evidence that he had of its former appearances, Halley boldly predicted its return in 1758 or 1759. He believed that before the predicted time arrived he would be in his grave, but with that thirst for fame which is the infirmity-shall we call it ?-of noble minds, and with a patriotic jealousy for the honor of his native country, he expressed a hope that, in the event of the comet's return, it would be remembered that its periodicity had been discovered by an Englishman.

As the period of the comet's return indicated by Halley approached, the calculation of the elements of its orhit was repeated with great care and labor, and under the guidance of the results, astronomers in all quarters were on the out-look for the expected mighty traveller. A Saxon farmer, near Dresden, of the name of Palitzch, first saw it on the 25th of December, 1758. In the winter and spring of 1759 it was seen by numerous observers, and it arrived at its perihelion on the 12th of March, just a month before the calculated time. Even that small error in these enormous calculations, and affecting the passage of the comet through an orbit of such prodigious extent, was owing in great part to the want, at that time, of an accurate knowledge of the masses of the planets Jupiter and Saturn, whose perturbing forces considerably affect the motion of the comet.

Halley's comet was again due in the neigh

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