When the alarm of an eclipse is given in a Hindu village, the whole population turn out to avert the impending calamity. The black disk of the moon encroaching upon the bright surface of the sun is believed to be the jaws of a monster gradually eating up the latter. Gongs are violently sounded, the air is rent with screams of terror and shouts of vengeance; and all this uproar is made with the hope of scaring away the dragon from his dreaded purpose. For a time their efforts are in vain. The glorious sun disappears gradually in the mouth of the voracious monster; but at last increasing din seems to effect its purpose. The monster appears to pause, and, like a fish that has nearly swallowed the bait, but, on second thought, rejects it, gradually disgorges the burning morsel. When the sun is quite clear of the jaws, a shout of joy is raised, and the villagers disperse with the pleasing satisfaction that they have done the luminary a good service. This is but a type of the human mind in its untutored state, when it is unable to rise to the conception of a God whose glory lies in the orderly and regular evolution of His works of providence.

It is the power of predicting the time of eclipses that has divested such phenomena of their terror. The most ignorant Hindu could hardly but be ashamed of his superstition, and have his faith in the gong shaken, if the astronomer told him beforehand the precise moment when the monster would come and depart. Eclipses, more than anything else, demonstrate the perfect regularity of the motions of the heavenly bodies, and of the wisdom of Him who so exquisitely adjusted to one another all the parts of the celestial machine. No doubt the whole nautical almanac, with its mass of figures, is full of predictions which manifest an order equal to that indicated by eclipses. Still, an eclipse, with its imposing phenomena, proclaims in the most emphatic manner the marvellous order of the heavenly host. An idea of the extreme accuracy with which the moon's position at any moment can be predicted, may be formed from the keen dispute at present going on in the Academy of Sciences between Leverrier and M. Delauny, in reference to the lunar theory of the latter, as compared with that of M. Hansen, the Danish astronomer. Our readers will recollect that to this last astronomer is due the merit of discovering the different density between the nearer and more distant hemispheres of the moon. The controversy turns on the value of a constant entering into the calculation, and the difference between the two views is only a space, represented by the one three-hundredth part of the moon's apparent diameter. Yet on these few seconds of space depends the result of an important question, on opposite sides of which the chief astronomers of our day are ranged. The Astronomical Society of London have virtually given their decision in favour of Hansen, by crowning him with their highest award of the gold medal. They have recognised his lunar tables as the complete solution of the grand nautical problem of finding the longitude at sea. The problem consisted in merely assigning, with absolute accuracy, the place of the moon in the heavens at any given time. Hitherto this was not done, as the perplexing and complicated irregularities of the moon's motion baffled all attempts to calculate her position with the requisite accuracy. There are even still some outstanding errors which are yet to be accounted for, but they are so small, that any further approximation would practically be of no service to the mariner.

Every time the sailor takes a lunar with his sextant, he has a practical illustration of the triumphs of astronomy in assigning at any moment the exact place of the moon in the heavens. Still every mind must feel the more startling effect produced, when, in an eclipse of the sun, the first impact of the moon coincides with the very beat of the clock assigned by the astronomer; and assigned, too, not as an empirical deduction from previously observed regularity, but as the result of the all-pervading power of gravitation, which not only produces the most bewildering inequalities, but furnishes, by its simple law, a key by which they may be all reduced to the most wonderful symmetry and order.

We have, however, on the present occasion, taken up the subject of eclipses, not so much with the view of illustrating the accuracy of astronomical calculations, as of turning the attention of our readers to the physical aspects of the total eclipse on the 18th of July next. No total eclipse has been witnessed in these islands for several generations. The last observed at Greenwich, was in 1715; and there was an interval of 375 years between this and the previous one. The chance of a person ever witnessing in his lifetime a total eclipse in any given spot of the earth's surface, is exceedingly small. The shadow forms only a narrow band on the earth's surface, and, though that strip of darkness will cross Europe six times during the remainder of the present century, yet comparatively few places will enjoy the spectacle. It is certain that none of the inhabitants of the British Isles, will ever see a total eclipse if they do not move beyond their own shores. But if the shadow does not come to us, we have the alternative of going to the shadow, And it so happens that the eclipse of July next, in regard to time and place, presents no ordinary temptation to the tourist, to plan his summer's trip so as to cross the path of the shadow.

It may, however, be asked, is it worth while to go much out of one's way to enjoy the spectacle? "We have seen eclipses very nearly total, and we can readily conceive one that is absolutely so. "Would it, then, really reward one to travel far to behold a sight which may differ so little from what we have already seen? We can give a very decided answer to this question. No approach to totality can give the slightest conception of, the effect produced the instant that the last thread of light is extinguished. The light of the sun is so intense, that while the slightest part of the disk is visible, the darkness is by no means alarming. The eclipse of 1857, which was nearly total, gave great disappointment to many who were led to expect something very appalling. Accounts of total eclipses were previously given, and it was a natural and popular expectation, that one so nearly total would produce effects very similar. But such was not the case. The darkness was no greater than that often produced by a passing cloud, and, in the case of many, the eclipse occurred without being in the least noticed. Partial and annular eclipses are now regarded as matters of mere curiosity, and a momentary glance upwards is regarded as ail that is demanded in the way of attention. It is far otherwise with the total eclipse. The gradual creeping of the moon over the disk of the sun, gives no preparation for the grand final effect when the last ray is quenched. It is felt not to be a matter of gradations so frightfully sudden is the darkness. There is no comparison between a man nearly drowned and drowned altogether, or between a man half over a precipice and over altogether; so there is no comparison between a nearly total eclipse and one absolutely total. As it is the last straw that breaks the back of the camel, so it is the extinction of the last line of light that produces the darkness that may be felt; and the " feeling of the darkness " is hardly a metaphor, as the borders of the terrible pall thrown over the earth can be actually seen swiftly floating past in the air .

In these days, when the passion for travel is so strongly developed, people are ready to go any distance to experience a new and strong sensation. They do not scruple to traverse the Atlantic, that they may gaze on the Falls of Niagara, or shoot the rapids of the St Lawrence; but such sights are not to be compared to a total eclipse, if measured by the power of stirring strong emotion. In an eclipse all things combine to deepen the effect; there is nothing out of keeping with the grandeur and awfulness of the spectacle. In viewing the Falls of Niagara, there is much to tone down the feelings of awe and wonder. Familiarity has destroyed man's reverence; merry, laughing, picnic-ing parties dispel the charm. Blondin exhibits his tight-rope antics in their very presence. The very birds despise their terrors, and dash heedlessly into the spray, to catch the stupified fish as they come tumbling down the liquid arch. The descent of the rapids of the St Lawrence, however daring the exploit may at first seem, fails, from the requisite accessaries, to produce a very powerful sensation. Even when shooting the Long Sault, there is no overpowering feeling. The Indian at the wheel, with his imperturbable matter-of-fact every-day expression; the old traveller, not caring to rise from the breakfast-table to look out on the tumultuous rush of waters; the air of security around, all combine to break the spell of that wonderful feat. It is quite different in the case of the total eclipse. All nature sympathises with and enhances your feelings of awe and mysterious apprehension. The earth, seas, sky assume a lurid, unnatural hue. An unearthly silence is felt-at the moment of totality. Every living thing catches the influence, and cowers under the great blank in the heavens. Beasts of burden lie down with their loads on the road, and refuse to move on. Swallows in their bewilderment dash against the walls of houses, and fall down dead. The dog drops its bone from its mouth, and does not venture to seize it again till the light returns. Chickens seek the shelter of the parent wing; and even ants halt in their tracks with their loads, and remain immovable till the shadow is past.

With such accessaries as the above, it cannot be wondered at that, in the case of man, however impassive his nature may be, a total eclipse never fails to produce feelings of mysterious awe. The most learned savant, as well as the most unsophisticated peasant, confess to such feelings. Even Mr Airy, the astronomer-royal, the impersonation of the calm and the abstract, confessed to very curious and indescribable feelings. It is, however, when men are massed together that the finest opportunity is afforded for watching the psychical effects of an eclipse. Such an opportunity was enjoyed by the French astronomers when observing the total eclipse of 1842 at Perpignan. The observers were stationed on the ramparts with their instruments; the soldiers were drawn up in a square on one hand, and on the other the inhabitants were grouped on the glacis, so that the station commanded the full view of twenty thousand upturned faces. The astronomers did not fail to watch the phases of feeling in the crowd, as well as the phases of the eclipse. The moment that the people, with smoked glasses to their eyes, marked the first indentiture in the sun's disk, they raised a deafening shout of applause, much in the way in which they would salute a military hero, or a popular actor. The moon gradually crept over the sun, and for a considerable time there was nothing observable but the ordinary loquacity of a French crowd. As the eclipse drew towards totality, the murmur of twenty thousand voices rapidly increased, each one telling his neighbour of the strange feelings coming over him. Suddenly the last filament of the sun's disk was covered, and at that moment a deep, prolonged moan, as from one man, arose from that vast crowd. It was like the stifled groan of the multitude witnessing a public execution, at the moment that the axe or the drop falls. The moan, however, did not mark the climax of high-strained feeling. The dead silence that ensued was the culminating point. Not a whisper was heard, not an attitude was changed, as with the rigidity of a statue each man stood and gazed upwards. So unearthly was the silence, that the beat of the chronometers was heard with painful distinctness. The heart of the universe seemed to cease its throbbings. Nature had fallen into a state of syncope. For two and a half minutes this dreadful pause continued. At the end of this period a thread of light burst forth; the tension was at once relieved, and one loud burst of joy rent the heavens. They could not restrain their transports of happiness, now that the dread, undefinable woe had passed over. They did not care now to look at the final phase of the eclipse, as the darkness wore off; they had beheld the crowning spectacle; they would not weaken the impression by looking at the partial obscuration, and soon the whole crowd melted away, leaving the astronomers to continue their observations alone.

"We have seen how the eclipse told upon a French crowd, noted for its impressible and demonstrative character. But there were also numer-ous illustrations of its power over individuals. Take one as a specimen:—A young boy, on the same occasion, was herding a few sheep in a lonely heath, under a cloudless sky; he felt a strange darkness coming over the face of nature, and at the moment of totality, he fled towards home, sobbing piteously. Before he reached the door, the sun burst forth, and in the transport of his joy, he clapped his hands, exclaiming, ''Beautiful sun! beautiful sun!"

We have viewed the total eclipse merely as a spectacle of surpassing grandeur; but it is one, too, of the greatest scientific interest, as throwing unexpected light on the physical constitution of the sun—

"Who could have thought such darkness lay conceal'd
Within thy beams, O sun! or who could find,
Whilst fly, and leaf, and insect stood reveal'd,
That to such countless orbs thou mad'st us blind!
Why should we then shun death with anxious strife?
If light can thus deceive, wherefore not life?"

If night can give us a surprise by revealing countless worlds, the eclipse can also surprise by revealing a new glory of the sun. When the totality is complete, a corona bursts out around the black circle, like the glory that surrounds the heads of saints in the pictures of the old masters. This corona has usually been observed to consist of two zones or concentric strata. The innermost is the brighter of the two, and the light is nearly uniform. The outer and fainter zone is diversified with radiating beams. In consequence of the light of the corona, the darkness is by no means so great as the darkness of night. The degree of darkness is best measured by the number of stars visible. In all the authentic accounts we have of total eclipses, none but the brighter stars have been visible.

The most remarkable and baffling phenomenon is the rose-coloured prominences seen in the innermost and brighter zone. They affect curious shapes; one, seen in the eclipse of 1851, has been designated the boomerang, another, the balloon. Some have been compared to the teeth of circular saws, others to the flames issuing from the top of a burning house, and driven aside by the wind.

The most important inquiry that suggests itself is, "Does this corona belong to the sun or the moon?" This point has been keenly disputed; but the general belief is that it is an appendage of the sun. Father Secchi, to whose discoveries in regard to the nature of the moon's surface we in a former article alluded, is disposed still to refer the phenomenon to the moon, and to explain it by means of his discoveries. According to his hypothesis, the corona is produced by the edges of the moon affecting, in a peculiar manner, the rays of light which pass across them. The much more probable supposition is that the corona is the atmosphere of the sun extending beyond its luminous disk, and that the red flames are substances floating in that atmosphere. In ordinary circumstances, the photosphere of the sun, or luminous envelope, is so overpowering, that the atmosphere, with the flames, is invisible. When, however, the eye is protected by the moon covering the luminous disk, the atmosphere at once is made visible. No plausible theory has yet been given to explain the nature of the red flames. A coincidence has been traced in the position of the flames and that of the dark spots of the sun ; and it has been conjectured from this that these dark spots are funnels in the luminous envelope, through which inflammable gases rise and are burned in the region of the corona or atmosphere, where they appear as red flames. The truth is, that we have almost no ground whatever, as yet, on which to base a theory. It was thought that during the last eclipse of 1851 several points would be set at rest; but the evidence was very conflicting, arising very much from the flurried state of feeling caused by the startling character of the phenomena, and their very brief duration. European astronomers are looking forward to the approaching eclipse with eagerness, as it is confidently expected that it will be conclusively settled whether the corona really belongs to the sun or the moon ; and, for this purpose, the attention will be directed to two points in the phenomena —first, whether the corona retains its symmetry, or continues concentric with the black circle of the moon during the totality ; and, secondly, whether, during the same period, the red flames change their position on the circumference of the moon. If there be a want of symmetry, and if the flames change their place, the evidence is conclusive that the appendage belongs to the sun.

Another point of interest will be the search for the newly-discovered planet Vulcan. It is expected that it will be readily found, from our knowledge of its approximate place.

To make amends for the imperfection of the testimony of the human eye in such unusual circumstances, it is intended to employ an artificial substitute, which will record the impression with due calmness and fidelity. This is to be done by applying a sensitive photographic surface to the telescope, instead of the human retina. In other words, photographic pictures of the eclipse are to be taken, and under Mr Be La Rue's superintendence, we may expect all that skill and experience can effect.

We are persuaded that many besides professed astronomers will seize this opportunity of beholding the grandest spectacle in nature. And why should they not ? It is not a matter specially belonging to the astronomer. It involves no profound calculations, nor demands any delicate astronomical methods. It is simply a physical phenomenon, which any intelligent observer can appreciate as much as the astronomer. Indeed, the astronomer with all his imposing instruments, has, as yet, contributed little more than any one might have done with the use of his naked eye. Any one who goes merely for the enjoyment of the spectacle, should discard all scientific pretensions, and abjure the use of instruments. The time of observation is so brief, that the attention would be distracted and the enjoyment destroyed by attempting to employ instruments.