Chinese, provided they be instituted and carried out in good faith, and with a proper deference to their time-honoured, though rather exceptional manners and customs.

It is well known that the Chinese are excellent calculators, and the universal employment of the abacus, or swan-pan, in the schools of the Celestial empire is, no doubt, the great cause of this. With that instrument, Sir John Bowring has told us, the Chinese youth has been as familiar as with his hemetrical classic, the first and most popular of his schoolbooks. From it he has drawn the most correct impressions of the relations of numbers one to the other, and he has acquired the habit of moving the balls on the wires of his swan-pan with wondrous rapidity. For the performance of decimal calculations this instrument, which we need not further describe, is especially valuable, and it is an excellent forerunner therefore of a decimal coinage.

On the whole, there is every reason to hope that the British Government and the authorities of the Mint will gain golden. opinions from both native and foreign residents at Hong-Kong, once the new coinage shall find its way into the channels and creeks of general circulation there.

URANUS.-SILVERED GLASS SPECULA.

OCCULTATIONS.

BY THE REV. T. W. WEBB, F.R.A.S.

URANUS.

If our readers have succeeded in finding Uranus, during a season when it has been almost an achievement to find anything, and still more, if they have effected the "raising of a disc". that is to say, if its apparent magnitude has increased in the ratio of the magnifying power, which is never the case with the spurious discs" of fixed stars-they have no reason to be dissatisfied. They have at any rate done what the celebrated Sir Joseph Banks, the President of the Royal Society for many years, failed to accomplish. The announcement of Herschel's discovery in 1781, though he considered it at the time to be probably a comet (its planetary nature being first suspected by Maskelyne), was received with some distrust; and I have been told by a friend (since deceased) of the discoverer, that the learned President, and several Fellows of the Royal Society, having been unsuccessful in searching for it, Sir William, then Dr. Herschel, had a portable tube constructed of silk, packed up his specula, left Slough, and gave the incredulous party

the meeting upon the roof of Somerset House, where, the planet having been duly exhibited, Sir Joseph Banks took off his hat and bowed to the illustrious astronomer, the others present following his example.

To advance beyond the mere exhibition of a disc would require a degree of optical aid which few amateurs have at com. mand; it may therefore, perhaps, be interesting to state some particulars as to this remote body, the result of investigations with the most powerful instruments. There seems great probability that it may be really a flattened spheroid, as this form appears to be the ordinary concomitant, if not the result, of rotation upon an axis, and an unrotating planet would be an anomaly, the existence of which ought not to be admitted excepting upon the strongest evidence. This idea is also well borne out by the analogy of Jupiter and Saturn; for Uranus is evidently a member of the same group with those great planets. It is a fact worthy of notice, that the curious interval in which such a multitude of asteroids, or more properly "planetoids," have been discovered during the present century, divides the solar system into two very unequal portions-an inner and an outer region, each district being distinguished by characteristics of its own. All the planets beyond the dividing space, notwithstanding striking individual peculiarities, have certain common points of agreement, in which they differ from those of the interior group; such as great magnitude, inconjiderable density, and a numerous retinue of satellites. When, therefore, we find so extensive a compression at the poles of Jupiter and Saturn, we should naturally expect a similar feature in the case of their next neighbour. Yet it is a question whether the amount of flattening, so conspicuous, even with small instruments, in those two great planets, is sufficient, in the case of Uranus, to be recognized even with the most powerful telescopes. Herschel, in 1782, considered the disc to be decidedly circular; in 1783,† 1792, 1794, and 1795, with various reflectors and magnifiers, he thought it slightly elliptical. Schröter, while contrasting it in 1802 with the newly discovered planet Ceres, speaks of its appearance, with his excellent 9-inch speculum, as that of a miniature Jupiter, except in the absence of ellipticity. Mädler, during some very fine weather in September, 1842, using a power of 1000 with the celebrated Dorpat achromatic, and measuring repeatedly 24 diameters at intervals of 15°, found a polar flattening To85, with an inclination of

=

Though only one satellite has been certainly discovered to attend upon Neptune, this will not be considered an exception, if we bear in mind the amazing distance of the object, and the great disproportion in magnitude which exists among the satellites of Saturn.

+ This date has escaped the notice of Arago.

=

=

axis 160° 40': having repeated a similar process in 1843, he gave the mean result This would seem beyond exception; yet it is, though disappointing, instructive to find that it has not been confirmed by the yet superior instruments of Struve and Lassell. In 1787 and 1789, Sir W. Herschel strongly suspected the existence of two rings, not concentric like those of Saturn, but perpendicular to one another: in 1792, however, he abandoned the idea. This as well as the preceding instance, shows the degree of caution to be exercised in admitting as certain the indications even of the finest instruments, when the object approaches the limit of visibility. Excepting Lassell on one occasion, no one has ever surmised the presence of a spot upon this minute disc, and even he, with a 2-feet speculum, and in the sky of Malta, failed in verifying its existence.

Considering the small proportion of light which Uranus receives from a sun only 1' 40" in apparent diameter, and amounting to only of what we enjoy, its disc is more luminous than might have been expected; and hence Gruithuisen was led to suppose that it may, in common with Jupiter and Saturn, possess some native light. A more natural solution for the fact, which is certainly a curious one, especially in connection with the distribution, already mentioned, of the planets into two dissimilar groups, might be found in the supposition of a highly reflective material.

Those marvellous, but as it seems well-attested, peculiarities of the satellites of Uranus, the high inclination of their orbits to the ecliptic (amounting to 78° 58′), and their retrograde motion, so contrary to every known arrangement in the planetary system, would render them most interesting objects, if there were a chance of catching sight of them; but for ordinary amateurs the case is perfectly desperate. I do not know the smallest aperture which could grasp them. Smyth considered 5.9 inches utterly powerless. Lamont saw two plainly, and a third on one occasion, with the great achromatic in the Royal Observatory at Munich, having an 11-inch object-glass. From their extreme faintness much uncertainty has existed both as to their number and their distances from the primary. Sir W. Herschel thought he had discovered six; Arago, by including all the observations, however doubtful, of all the observers-the two Herschels, Lamont, Otto Struve, and Lassell-has made up eight; but evidently not much to his own satisfaction, nor, it may be presumed, that of any one else. In 1852 Lassell subjected Uranus to a long and most careful scrutiny, using a magnificent speculum of 24 inches in diameter, brought to such perfection by his own polishing machine, as to carry, in the air of Malta, a power of 1018 upon this feeble disc with "a remarkably hard

and sharp edge:" under these most propitious circumstances he was soon led to say, "I think it is high time that Uranus's establishment should be reduced. He has been luxuriating these many years with a retinue that I really believe does not belong to him, and therefore he must be cut down to four attendants, until some astronomer arises rich enough to present him with some more ;" and his final conclusion was thus expressed :-" I am fully persuaded that either he has no other satellites than these four (viz., the two first seen by Sir W. Herschel, and two others added by himself), or if he has, they remain yet to be discovered." From this decision there can be no appeal, excepting to the observer himself, who has now the fullest opportunity of revising it. He went out again more than twelve months ago to the same admirable station, with its hundred miles or more of sea in every direction, its equable temperature, and its peculiarly tranquil and transparent sky. He is armed with two still more superb specula of twice the diameter, and consequently four times the light-collecting capacity of his former one, and through the simple expedient of protecting them by a coat of varnish, their exquisite surfaces were preserved untarnished during the voyage. His observatory has been re-erected, and he has, it is known, long ago renewed his examination of Uranus. In the wish that in this, and all other respects, the result of his spirited expedition may answer his most earnest expectations, every reader of these pages will cordially join.

SILVERED GLASS SPECULA.

The old refracting telescope, of which there now remain so few specimens of any considerable size, that our readers may probably never have had an opportunity of seeing one, was by no means a contemptible instrument. The work that it accomplished in the hands of Huygens, Bianchini, Cassini, Maraldi, and other observers of the two last centuries, is a sufficient proof of its capabilities. While doing full justice to the admirable perfection of modern workmanship, we must feel that nothing can throw discredit on those who so fashioned the simple objectglass of former days that it could detect five of the satellites of Saturn, and show, even with an aperture of barely 21 inches, and a power of 90, the principal division of that planet's ring.* But however beautiful might be the figure and the polish of the lenses of Campani or Christian Huygens, the cumbrousness and unwieldiness of the machines which carried them were a

I have seen, indeed, the latter object distinctly with a power of 80 on 3% inches, but only in such a way as to show that I possessed no great advantage over the original discoverers of that minute black line, which, according to De La Rue's measures, subtends an angle of only 0":94, but to which W. Struve, Secchi, and Bond assign not so much as half that breadth-about 0"4.

most serious drawback, and what we now call a "night's work" at an observatory would then have implied "work" indeed. The labour involved in such an undertaking may be estimated by any one who will look at the curious delineations appended to Bianchini's Hesperi et Phosphori Nova Phænomena; and though the ingenuity of Christian Huygens did something for observers in dispensing with the tube and all the marvellous appliances for bracing and stiffening it, the mere operation of getting the object-glass to a sufficient altitude was no trifle. So Derham found it when he had the loan of the 123 feet refractor, then, and still, belonging to the Royal Society with characteristic simplicity he lays before the public his "chief inconvenience, the want of a long pole, of 100 or more feet, to raise my long glass to such an height as to see the heavenly bodies above the thick vapours.

But, as

I have been at considerable expenses already about these matters, and this I am informed would amount to £80 or £90, I thought it much too great a burden for the yearly income of my living."

The fate of such an apparatus was therefore not surprising when the invention of the reflecting telescope by Gregory and Newton, and of the achromatic by Hall and Dollond, reduced the length to one-tenth or one-twelfth part, without any sacrifice of distinctness. It sunk, never to be revived again; and ever since, the two constructions which superseded it have been competing for the preference. The reflector was the older, and in the hands of Short, about the middle of the last century, attained extraordinary perfection; but the achromatic, as the more convenient and less liable to injury, rapidly gained ground upon it, and would have quite outstripped it, but for the peculiar difficulty of procuring good glass. This was so great that even as late as 1829, Dollond had not been able to obtain a 44-inch disc of flint glass fit for such a purpose during the previous five years, nor one of 5 inches during twice the time; and hence the re flector maintained its superiority for the purposes of astronomical discovery. In the hands of Sir W. Herschel in England, and Schrader in Germany, the metallic speculum assumed gigantic proportions, and the rejection of the small mirror in the "front view" of the former was attended by an increase of light that for many purposes more than counterbalanced a slight want of accuracy in definition. But the achromatic was yet to have its turn. Fluids, as substitutes for the obnoxious flint glass, had not fully answered the purpose. Blair's beautiful adaptation of them had remained unnoticed, and seems to have been ill-suited to large apertures. Barlow's "correcting lens" of sulphuret of carbon had not been entirely satisfactory-it might possibly have been rendered so, but it came too late.