path of the stranger lies as far beyond what had been deemed its extreme confine, as that limit is removed from the sun. The first moment of his "attack" upon Saturn, upon completing the forty-feet reflector, he saw a sixth satellite, and a seventh a month later, now called Mimas and Enceladus. But Herschel realised his most surprising results from the observation of the sidereal heavens. The resolution of nebula and the Milky Way into an infinite number of stars - the discovery of new nebula of various forms, from the light luminous cloud to the nebulous star—of double and multiple stars of the smaller revolving round the greater in the binary systems; these were some of his revelations to the world, as night after night, from dewy eve till break of dawn, he gauged the firmament. Caroline Herschel was the constant partner of her brother in his laborious undertakings-submitting to the fatigues of night attendance - braving with him the inclemency of the weather-noting down his observations as they issued from his lips and taking, as the best of all authorities reports, the rough manuscript to the cottage at the dawn of day, and producing a fair copy of the night's work on the ensuing morning. He died in 1822; but she survived to 1848, witnessing the heir of his name recognised as the heir also of his talents and fame. It was one of the conceptions of this remarkable man- as bold an idea as ever entered the human mind-that the whole solar system has a motion in space, and is advancing towards a point in the heavens near the star à Herculis. General opinion is now in favour of the idea, that not only the solar but the entire stellar universe revolves around some mighty centre. The nineteenth century commenced with a fresh ingathering of members into the planetary family. It had been deemed a matter of surprise that the immense interval of about 350 millions of miles between Mars and Jupiter should be void, when only spaces varying from 25 to 50 millions divide Mars, the Earth, and the inferior planets. Keppler had therefore started the conjecture that a planet would be discovered in the vast region between the two former bodies; and thus bring it into something like proportion with the spaces between the latter. This idea was confirmed by a curious relation discovered by Professor Bode between the mean distances of the planets from the sun. It is to the effect, that proceeding outwardly from the sun, the interval between the orbits of any two planets is about twice as great as the inferior interval, and only half the superior one, except in the instance of Mars and Jupiter. Uranus had not been discovered when Bode arrived at this remarkable analogy, but the distance of that planet being found to correspond with the law, furnished a striking confirmation of its truth. If the third term 10 be taken to represent the distance of the earth, the third planet, in order from the sun, the remaining terms will represent very nearly the respective distances of the other planets. Thus, Mercury. Venus. Earth. Mars. Jupiter. Saturn. Uranus. The fifth term in the series is unrepresented, except by the exaggerated leap from Mars and Jupiter. It will be perceived, that while there is a striking approach to duple progression in the succession of distances, the condition is not exactly fulfilled; and as it fails utterly in the case of Neptune, the last discovered planet, Bode's law, as it is called, is purely empirical. The void in the series between Mars and Jupiter, so convinced the German astronomers of the existence of a planet to occupy it, that a search for the concealed body was commenced. The anticipation was soon substantially realised by the discovery of four planets-Ceres, Pallas, Juno, and Vesta, revolving round the sun at a mean distance of one hundred millions of miles from Mars, so small as only to be telescopic objects. This discovery we owe to Piazzi, Olbers, and Harding. Some singular features, without parallel in the planetary system, such as their close contiguity, the intersection of their orbits, with their diminutive size,-Vesta not being much larger than the Spanish peninsula,-led to the surmise that these bodies are fragments of a planet which once revolved in their mean path with a magnitude proportionate to that of its neighbours. The possibility of such a disruption cannot be denied the revolution of the fragments round the sun would follow in obedience to the mechanical laws by which the system is governed— but the point is obviously one of those questions which must remain entirely hypothetical. The career of planetary discovery which began with the century, was resumed in the year 1845; and has since been continued with most surprising results. Another miniature orb, Astræa, discovered by M. Hencke, was then added to the family of minute worlds rolling between Mars and Jupiter; and in one year alone, 1852, no less than eight such bodies were found. The known number at the time of writing these lines (1st of September 1857) is forty-five. Besides this, in the present age, the members of the solar universe have been increased by the detection of the primary planet Neptune, attended with a satellite; and of an eighth satellite of Saturn, called Hyperion, remarkable for its simultaneous discovery by independent observers, in 1848, Mr Lassel of Liverpool, and Mr Bond of Cambridge, in the United States. The addition of a primary planet to our system demands a brief notice. Observations upon Uranus had shown the motions of that planet to present great irregularities, which could not be explained by the action of Jupiter and Saturn; and after carefully examining the analytical theory of Uranus, Leverrier, a young academician of France, in the summer of 1846, published the elements of an undiscovered planet, the cause of the perturbations. He boldly predicted its existence, calculated its mass, and referred to its place in the heavens; and scarcely a month afterwards, on the 23rd of September, the hitherto concealed object was found by M. Galle of Berlin. But it has only been by accidental circumstances that France has the honour of this remarkable achievement. Upon retiring from the chair of the British Association, a fortnight before the observation of M. Galle, Sir John Herschel, in remarkable words, referred to the astronomical events of the past year, observing that it had given a new planet (Astrea) to our list, and adding, "it has done more, it has given us the probable prospect of the discovery of another. We see it as Columbus saw America from the shores of Spain. Its movements have been felt trembling along the far-reaching line of our analysis, with a certainty hardly inferior to that of ocular demonstration." This striking paragraph, as subsequently explained, had a twofold reference to the calculations of Leverrier, and to a similar investigation previously completed by Mr. Adams of Cambridge, the independence of the investigations, and their very nearly coincident results, justifying the confidence so strongly expressed by the speaker. Mr. Adams commenced his theoretical researches in January, 1843, recommenced them upon larger data in February, 1844, and obtained results for the heliocentric longitude, eccentricity of orbit, longitude of perihelion and mass of an assumed exterior planet, deduced entirely from unaccounted-for perturbations of Uranus. These results were communicated to Mr. Challis, the Professor of Astronomy at Cambridge, in September, 1845. In October they were in the hands of Mr. Airy, the Astronomer Royal, whereas Leverrier's labours were not made public till the June of the year following. They were not then so complete as those of Mr. Adams, indicating merely the probable position of the hypothetical planet, while the latter had given values respecting its mass and the form of its orbit. The correspondence between two independent inquiries as to position inspired confidence, and Mr. Airy recommended a systematic search for the object, which Mr. Challis commenced on July 29. It now appears that, on August 4th and 12th, he actually seized the planet, and recorded two positions of it, but did not recognise it, through not comparing his observations, which a pressure of occupation, and an impression that the discovery required a much more extensive search, prevented. But for this, and the non-publication of the Cambridge mathematician's results at the time they were forwarded to Mr. Airy, the honourable position of M. Leverrier would have been occupied by Mr. Adams, and that of M. Galle by Mr. Challis. The progress of astronomical discovery which has now been briefly traced, reminds us of the obligations we owe to those who have gone before us. How incumbent the duty upon us, then, as we have largely benefited by our predecessors, that, as faithful stewards of their gifts, we should hand them down to posterity with an increase of value! How grand, and yet how simple, those views of the universe, upon the evidence of which we are now invited to gaze! The Sun, a central orb, attended by a stately cortège of planets, forming a system under the empire of law,-a system not unique, but a general type of others as countless as the members of the stellar host, whose front ranks alone come within the range of telescopic vision ;-systems, probably, not physically insulated, but bound together by fine relationships, the nature of which, judging from the progress of the past, it is not arrogant to presume, will yet be revealed to the understanding of man! These are not ingenious theories-splendid conjectures-but established facts, and sober anticipations based upon them. To live and learn is the high vocation of humanity, one of the appointed ends which the great Artificer of existence contemplates in its continued series; the generations that are to come improving upon the acquirements of that which now is. Nor can we fix any limit to the growth of knowledge in relation to the physical universe, clear and insurmountable in the present state as are its bounds with respect to the spiritual world. Who can descry a resting point in the wilderness of space?-discern a barrier to the range of the creation? Vast as are the regions that have been entered, there are vaster amplitudes unapproached beyond them, towards which the mind may advance in endless progression; often indeed faltering in the pilgrimage beneath the burden of those conceptions of space and magnitude which immensity suggests, but still going onwards. will infallibly keep the appointment. In countries favoured with a more transparent atmosphere than our own, the day-spring, the commencement of terrestrial nature's diurnal audience with the solar presence, is a scene of great combined beauty and magnificence. Faint rosy-coloured streamers are early indications of the point of sunrise; these rapidly become more distinct, and are followed by resplendent saffron hues, from that of burnished gold at the horizon, to the lighter shades gradually fading upwards into the pure cerulean of the illuminated sky. A recent pilgrim from the Western world to the sacred sites of the East, during his stay at Athens, went to witness the sunrise from the Acropolis, amid the solemn grandeur of its desolations. Seated within the ruins of the Parthenon, commanding a view of the horizon through the columns of the eastern portico, he awaited from the grey dawn the appearance of the orb of day. Gradually the sky became so resplendent in the direction of the advancing luminary, as to render it impossible to determine the precise point where his presence would be revealed. The tops of the northern mountains caught his beams, and some light fleecy clouds seemed changed into liquid gold, as, hovering over mount Hymettus, they met the rays of the sun. At length, the eye encountered the solar glory, lighting up the columns and marbles of the Parthenon with a silvery splendour. It was one of those moments in the life of man, says Robinson, the traveller in question, that can never be forgotten. In our own latitude, the sunrise is a spectacle of surpassing interest and beauty, as viewed from the summit of Snowdon, or from some eminence overlooking the sea, in a propitious state of the atmosphere. The progressive illumination—the variegated colours deepening and brightening that are pencilled on the sky-the growing distinctness of the superficies, whether field or flood-the retreat of mists and vapours glittering in the sunbeams while vanishing before their action;-combine to form a scene of visual beauty which has few parallels in the realms of nature. Light is sensibly transmitted to us while the sun is below the horizon. This is occasioned by the refractive and reflective properties of the atmosphere. By the former, the place of the luminary in the heavens is optically raised; and morning and evening, when the lower limb appears to rest upon the horizon, the entire body is actually below it, and would be invisible but for the refraction of the rays. This effect is only produced while the depression is within 33', which is rather more than the sun's greatest apparent diameter. At a further distance from the horizon, the rays pass over our heads into the upper regions of the atmosphere, and their direct transmission to the eye ceases, But they continue to reach us for an interval by reflection from the illuminated atmosphere, and produce the morning and evening twilight, the gradual transition from darkness to light, and from light to darkness. It is owing to the particles of air possessing the property of successively reflecting and re-reflecting the solar light, scattering it in every variety of direction, that all those objects are visible to us in the daytime, which are indirectly situated with reference to the luminary. Without it, the cloudless sky at noon, now so blue and brilliant, would present the blackness of darkness, with the exception of the places occupied by the sun and the stars. The latter would be as visible by day as at midnight, while no object would be perceptible, not receiving the direct sunbeams. It is not impossible but that at midnight, in the hour of the deepest gloom, some of the solar influence may be transmitted to us by an infinite number of reflections, so reduced, however, in its amount and power as to be imperceptible. The period of the sensible reflection of light from the sun, or the twilight, is generally supposed to be confined to his depression eighteen degrees below the horizon. The limit of depression, however, at which the greatest observed darkness commences, varies in different climates. In the torrid zone it has been found to be between sixteen and seventeen degrees; and in France between seventeen and twenty-one. The duration of the twilight is different at every different latitude on the earth, and it varies in the same |