the circle itself, or within several degrees of it. They are thus confined to two belts of the solar surface, parallel to its equator, corresponding in some degree to the two temperate zones of the earth.

Intervals of some length have occurred, during which the disk of the sun has been comparatively pure. This was the case from the year 1650 to 1670; and in 1724 the surface appeared unblemished. But from 1611 to 1629, according to Scheiner, it was never free from tarnish, except for a few days in December 1624. At a more recent date, scarcely a year has passed without spots being seen, many of which have been of great magnitude. It is supposed by Schwabe, whose observations have been continued without intermission for more than thirty years, that the extent of the solar surface obscured by spots increases and decreases periodically, the length of the period being eleven years and forty days. This remarkable conclusion has attracted great attention; and upon the suggestion of Sir John Herschel, a photo-heliographic apparatus has lately been established at Kew, for the purpose of depicting the actual state of the solar disk from time to time. It has been thought, that spots of vast extent, or unusually numerous, may have the effect of depressing the terrestrial temperature, and thus affect the fertility of the seasons. But so far from such an inference being in harmony with observed facts, some of our warmest seasons have coincided with an accumulation of spots on the sun.

Besides the dark spots, or maculæ, as they are called, the telescope has disclosed other interesting appearances on the sun's disk. There are parts brighter than the rest of the surface-luminous aggregations-to which the term faculæ (little torches) has been applied. They occasionally exhibit a round form, but have generally an extended, ridge-like shape. Though commonly seen in the immediate neighbourhood of spots, they sometimes appear alone, in which case they are almost always the precursors of spots, which become visible on the following day. Messier was frequently enabled by these brilliant indications to predict the appearance of spots twenty-four hours before they actually presented themselves on the disk. While the faculæ are confined to the "royal zone," or region of the spots, the remainder of the solar surface is diversified with minute luminous specks and streaks, of varying brightness. These are bordered by more obscure parts, in which a multitude of small pores are observed, as black as the nuclei of the spots. The resulting mottled and corrugated aspect of the sun, Herschel compared to the roughness of an orange.

Conjecture has been busy respecting the nature of these appearances, their cause, and probable indications respecting the physical constitution of the body to which they belong. The early observers, indulging the vagaries of imagination, supposed the spots to be the fuel of the solar furnace, or ashes floating on the surface of an abyss of combustion, or the smoke of volcanic explosions. But the views first broached by Dr Wilson of Glasgow, founded upon a minute examination of their peculiarities, substantially adopted and amplified by Herschel, now generally obtain with astronomers. It seems scarcely to admit of doubt, that the sun is a solid body, surrounded by two envelopes, suspended in a transparent atmosphere; the upper one luminous, forming the visible surface; the lower obscure, a layer of dense clouds, highly reflective, throwing back the light of the upper regions. In these strata, temporary openings or rents are supposed to be made by currents operating from below, analogous to the hurricanes and tornadoes of our tropical districts. The altered appearance of the spots, as they are carried round by the solar rotation, strikingly confirm the fact that they are excavations; for after passing the centre of the disk, the penumbra is impaired on the side nearest to it, and gradually disappears; then the nucleus is nipped on the same side, till it vanishes; and then, finally, the penumbra on the opposite side begins to contract, narrows to a line, and is carried out of sight. These variations are exactly those which depressions will present in the course of rotation. Adopting this view, the nucleus of a spot is the exposed dense body or solid substance of

the sun; the penumbra is the cloudy interior surrounding stratum; and the faculæ, or bright ridges, are accumulations of the exterior luminous matter, heaped up by the violent local agitations. In its interior physical constitution, therefore, that magnificent phantom, or globe of fire, which the ancients conceived the sun to be, is, in all probability, an opaque substance, like the ground we tread upon; and, correspondingly, the atmosphere of our own globe is in a state of constant mutation. It is sometimes charged with clouds, which will completely hide the surface from view at no considerable distance from it. These are often rapidly rent asunder, gathered into distinct masses, and driven again into conjunction, affording transient glimpses of the earth to the adventurous aeronaut; circumstances which are apparently analogous to the superficial solar changes, though comparatively upon a most puny scale.

If this view of the constitution of the central globe be correct, there are strong resemblances between the sun and the bodies circulating in the system. They exhibit a family-likeness, being opaque masses, having a motion of rotation, and rotating in the same direction. In fact, according to Herschel, the sun appears to be nothing else than a very eminent, large, and lucid planet, evidently the first, or rather the only primary one of our system; and because of this analogy, in regard to solidity, atmosphere, and diversified surface, he was led to infer that it is most probably inhabited by beings whose organs are adapted to the peculiar circumstances of that vast globe. We feel it difficult to embrace this conclusion, from the fact of the solar rays producing, at the distance of so many millions of miles, a heat so considerable, that it must be intense and insufferable on the sun's surface, inferred to be far greater than that of the strongest blast furnace. But heat is only produced by the solar influence when it comes into contact with a substance that combines with it. Various experiments and familiar circumstances prove this to be the case. If the solar radiation collected in the focus of a powerful lens is thrown into the air, and continued there for a considerable time, no sensible heat will afterwards be perceived at the place, though had the most incombustible object been exposed there, such as gold or platina, it would have been fused. The eternal snow rests upon the summits of high mountains, which receive the direct influence of the sun's rays, while in sheltered parts of valleys below, receiving only their indirect influence, there is overpowering heat. The higher in the regions of the atmosphere an aeronaut ascends, the more intense is the cold, though there is nothing to interrupt the solar influence. Heat, therefore, is only generated by the sun's rays, when they unite with caloric, or heat in a latent state. We may conceive, then, the temperature of the sun's luminous atmosphere to be greater than that of any artificial heat which chemistry or galvanism can produce; yet the great globe itself may be constituted incapable of any chemical combination with the rays of the brilliant atmosphere without, beyond a certain extent, and if so, a temperature consistent with animal and vegetable life may there exist.

It is not, however, unlikely that the penumbra of the spots,-the stratum of dense clouds below the vividly resplendent visible surface of the sun,-may officiate to moderate the effect of the exterior atmosphere. Sir John Herschel, referring to that inner curtain of the mighty orb, remarks, "That the penumbral clouds are highly reflective, the fact of their visibility in such a situation can leave no doubt." They may thus serve the purpose of effectually defending the sclar body from the insufferable light and heat of the outermost surface, furnishing the solid nucleus of the luminary with a moderate temperature by their friendly interposition.

In the class of solar phenomena, Eclipses of the sun are always interesting, and sometimes imposing events. Few occurrences have given rise to more anxious feelings in the human breast, or have been watched with more unfailing curiosity. We are so familiar with their physical causes, and can predict with such nicety the time of their appearance,

that it is impossible for us to estimate the impression they would make upon the ignorant mind, transpiring under circumstances favourable to their full effect. To behold the sun, after shining in all its glory, apparently lose a part of the disk, become more indented, and then entirely invisible, while perhaps not a cloud has appeared upon the sky to account for the change of aspect; to witness nature in the clear day suddenly invested with an unaccountable gloom, the larger stars becoming distinct, and the brute creation exhibiting symptoms of restlessness and alarm; to feel a chilling cold supplanting the fervent heat of noontide,-these are peculiarities calculated to excite the consternation of uncivilised tribes, as well as of nations unacquainted with their true natural explanation. They have accordingly arrested the tide of battle, and perplexed monarchs with fear of change. In the first year of the Peloponnesian war, on a summer afternoon, there was an eclipse of the sun that was nearly total. Thucydides states, that the sun looked for a time like the crescent of the moon, and some stars appeared, but the full orb shone out afterwards in all its lustre. Pericles, according to Plutarch, was then on board his galley, about to proceed on a warlike expedition; and it required some address on his part to quiet the apprehensions of his troops, who looked upon the darkness as an unfavourable omen. Not many years afterwards, when the Athenians were in desperate circumstances in the harbour of Syracuse, and had resolved on retiring, an eclipse of the moon happening at the hour appointed for the retreat, excited their alarms, caused a delay, and led to the destruction of both fleet and army. Columbus once rescued himself from circumstances of great difficulty, when in want of provisions which the Jamaicans refused to supply, by means of a lunar eclipse. Knowing that it was nigh at hand, he announced it to them as a token of the anger of the Great Spirit on account of their inhospitality, which had the desired effect when the beautiful orb began to be impaired. Chronology has derived much valuable assistance from the connection which superstitious fear has recorded between particular events and these phenomena, for eclipses may be calculated thousands of years backwards with the same precision as forwards. Thus the coincidence between a total eclipse of the sun, a rare occurrence in the same region, and the battle between the Lydians and Persians, establishes the date of the latter; and the very day on which the great battle of Arbela was fought is likewise known from its taking place eleven days after an eclipse.

A solar eclipse is occasioned by the dark body of the moon interposing between the sun and the earth, and deflecting a shadow upon the latter. The shadow cast by an object is merely an interception of the light of some illuminating body, and has its shape and extent

determined by the form and relative magnitudes of the two. If the moon were as large as the sun, her shadow would be cylindrical, like the first figure, and of an unlimited length. If she were of greater magnitude it would resemble a truncated cone, the diameter and length increasing to an indefinite extent, as in the second figure; but being immensely inferior to the sun, she projects a shadow which converges to a point, like that in the third figure. This shadow, at the distance of the earth from the moon, can never be more than about a hundred and

seventy miles broad; and consequently the sun can never be totally eclipsed at the same instant over a greater extent of terrestrial space. But as the earth is continually moving, the shadow is a passing traveller, and sweeps over it; no total obscuration of the sun lasting longer at one spot than about eight minutes. Although the limits within which an eclipse is total are very circumscribed, it will be more or less partial over an area having a diameter of five thousand miles. In the diagram, lines

drawn to the earth from the upper and lower limbs of the sun and moon define the conical
shadow projected by the latter, or the umbra,

occasions a total ob-
Similar lines drawn

which, wherever it falls,
scuration of the solar orb.
to the earth along opposite edges of the two
bodies define the limits of a fainter shadow, or
the penumbra, caused by the moon only hiding
parts of the sun's disk; and, within the space it includes, the eclipse is more or less partial,
according to the situation of an observer.

As a general rule, it may be stated that an eclipse will diminish in magnitude about
one digit for every two hundred and fifty miles from the centre where it is total—a digit
being the twelfth part of the solar or lunar surface. The lunar shadow may, however,
terminate, when the earth is in a direct line with it, without reaching its surface. When
the sun is at the least distance from us, and the moon at the greatest, the shadow will
fall short of our globe by about twenty thousand miles, though when these elements are
reversed it is sufficiently long to extend nearly the same distance beyond us. In the
former case the sun has his greatest apparent diameter, and the moon her least. She is
unable, therefore, to cover his entire face, and appears projected upon his disk, with a
slender ring of dazzling light around her dark body. This is termed an annular eclipse,
from the Latin, annulus, a ring.

An annular eclipse is a rare occurrence.

1847, was very imperfectly observed owing to cloudy weather.
There may be five solar eclipses in a year, and the least number which can take place
is two. As the moon passes through that part of her orbit which lies between the sun and
the earth once a month, we should obviously have an eclipse every month, every new moon,
if she moved in the plane of the earth's orbit. This is, however, not the case-the lunar
path is inclined to that of the earth. She is above it during one half of her course,
and below it during the other, crossing it twice a month at two opposite points, called her
nodes. It is only when the moon is between the sun and the earth, at or very near her
node, that is, when her path cuts the plane of the earth's orbit, that she intercepts to us
the solar light, and eclipses occur; at other times, she passes either above or below the

7

sun as seen from the earth, and the earth passes above or below her shadow. Owing to the irregularity of the moon's motions, she does not cross the plane of the earth's orbit at the same point in every revolution, but these points shift through a certain interval, after which the same change is repeated, and the same cycle of eclipses occurs. This interval is eighteen years and about eleven days, a period early discovered by the Chaldean astronomers, and used for the purpose of foretelling eclipses. Thus, on the sixth of May 1845, there was a solar eclipse; and if we add to this era the ecliptic period just named, we are carried on to the seventeenth of May 1863, which will be the epoch of another. The complete period is 6585 days, 7 hours, 424 minutes nearly. But though the eclipses of each cycle correspond, and may be regarded as identical with respect to the earth in general, they vary in their appearances, and as to the localities in which they are visible. There was an eclipse of the sun visible at the north pole in the month of June 1295, but ever since, it has been proceeding more southerly. It made its first appearance in the north of Europe in August 1367. It was central in London in 1601, which was its nineteenth return; and nearly so again on the 15th of May 1836, its thirty-second appearance. At its thirty-ninth return, in August 1880, the lunar shadow will fall south of the equator, and continue receding from it, until its seventy-eighth appearance will be at the south pole, on the 30th September 2665.

Though solar eclipses are of common occurrence, yet a total one depends upon a conjunction of so many circumstances, that the spectacle happens only on very rare occasions, even anywhere on the surface of the earth. Especially at the same place, or within convenient distance of it are the opportunities for observing the phenomenon few and far between, so that entire astronomical lives have passed away without being gratified with the sight. Halley, in a paper on the total eclipse of the sun which happened at London on the 3d of May 1715-the reign of George I.-remarked, that there had not previously occurred a similar event, visible in that city, since the 20th of March 1140-the reign of Stephen—an interval of five hundred and seventy-five years. "I forbear,” he observed, addressing the Royal Society, "to mention the chill and damp which attended the darkness of this eclipse, of which most spectators were sensible and equally judges. Nor shall I trouble you with the concern that appeared in all sorts of animals, birds, beasts, and fishes, upon the extinction of the sun, since ourselves could not behold it without some sense of horror." One of his correspondents who was stationed on an eminence on Salisbury Plain, wrote to him as follows: "It was the most awful sight that I had ever beheld in my life. We looked in vain for the town of Amesburg, situated below us; scarcely could we see the ground under our feet. So deep an impression has this spectacle made on my mind, that I shall long be able to recount all the circumstances of it with as much precision as now." The total obscuration lasted 3 minutes, 22 seconds. The planets, Jupiter, Mercury, and Venus, with the stars, Aldebaran and Capella, were visible to the naked eye.

A partial solar eclipse, however considerable, gives not the faintest idea of what a total one is, as to the obscuration, the chill, and the altered physiognomy of heaven and earth. The "Saxon Chronicle" records of the eclipse in the reign of Stephen :-"In the Lent the sun and the day darkened about the noontide of the day, when men were eating; and they lighted candles to eat by. Men were very much struck with wonder." Of the same event, William of Malmsbury states, that "while persons were sitting at their meals, the darkness became so great, that they feared the ancient chaos was about to return, and upon going out immediately, they perceived several stars about the sun." An eclipse visible in Scotland in 1433, was long remembered by the people of that country as the Black Hour; another in 1598 was similarly commemorated by the inhabitants of the border counties as the Black Saturday; and a third in 1652 gave rise to the expression