will collect enough to dazzle and perplex the eye. An easy remedy, however, is open to us in daylight observations, such as we may now be supposed to have before us. There, ladies and gentlemen, is a lovely object-a half moon, of exquisite delicacy and pearly hue, differing, however, from our satellite in the much fainter aspect of the inner part of the semi-disc, towards the rectilinear edge. And that half-illuminated planet, as you now see it in the telescope, appears to you four times as large as the moon to the naked eye. Impossible, Mr. Astronomer! you tell us some strange things that we are willing to believe; but this is really going rather beyond the mark. Just so. We did not imagine you were likely to believe it at first. Few people, till they are accustomed to telescopic vision, have any idea of the size which objects appear. They always look too small for the supposed power. Yet our statement is not assertion, but demonstration. We are using an eye-piece magnifying three hundred times; Venus is now about twenty-four seconds in diameter; the Moon is nearly thirty minutes; by a little easy arithmetic you may fully satisfy yourselves of the fact. But how are we to know that your eyepiece does magnify three hundred times? That, indeed, you must take upon trust; it requires a little mathematical knowledge to understand the demonstration, but the demonstration itself is as unquestionable as that five times sixty are three hundred. But, if the moon were now in a suitable position, we would give you a very easy proof indeed-a strictly ocular demonstration; for you should look at the same time with one eye at Venus in the telescope, and with the other eye at the moon out of the telescope-no difficult matter when they are near together; and then, if you do not find that the planet's image would cover the moon four times over, we have nothing to say. But why it is that these telescopic images appear so much too small is rather a puzzle. The explanation probably lies in

the

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opposite circumstances of vision; in one case, a free open sky; in the other, a narrow limited field; natural seeing against artificial peeping; the perfect sharpness of the real object against the comparative definition of the optical image some or all of these may help the difficulty-but if they do not, we must refer you to Herschel or Lassell, or some one who can explain it better; but the fact is certain. Now look again at that beautiful planet; you think you can make out spots and mottlings and wavering uncertain shades, and perhaps you do; and you may look on twenty evenings and have the same impression, and yet never be able to fix on any certain form or outline; and you would have many of the first astronomers to bear you company; such is the testimony of the present Herschel in his admirable Outlines of Astronomy; the intense lustre of its illuminated part dazzles the sight, and exaggerates every imperfection of the telescope; yet we see clearly that its surface is not mottled over with permanent spots like the moon; we notice in it neither mountains nor shadows, but a uniform brightness, in which sometimes we may indeed fancy, or perhaps more than fancy, brighter or obscurer portions, but can seldom or never rest fully satisfied of the fact.' But old Bianchini the Roman ecclesiastic, who seems, by the way, to have been a very respectable estimable kind of man, was more fortunate in 1726. The telescopic apparatus of that day was alarming in its cumbrousness, and one of its arrangements reminds us somewhat of the mainmast of a schooner entangled in a gigantic pair of lazytongs; yet he thought so highly of it as to have it engraved for the benefit of posterity-and in some respects it deserved it, not only for its ingenuity, but as a specimen of the age, and of the brave pursuit of knowledge under difficulties.' It was, however, by the simpler contrivance of Huygens, who tied the object and eye-glasses together with a long line, that Bianchini

was enabled to detect and map out a series of continents and oceans, as he thought them, of which Cassini had previously made out some traces, but which—at least in their connexion and completeness -have escaped every subsequent observer, till De Vico and other 'astronomers of the Jesuit fraternity rediscovered them in 1839 with a 6-inch achromatic by Cauchoix, the property of their society, harboured in the observatory of the Università Gregoriana of the late Pope. That instrument certainly showed them some queer things before the Roman insurrection in 1848 sent it, with some of the brethren, on a Transatlantic journey; and the observers paraded them before the astronomical world in a fashion which showed that their scientific must have been very inferior to their theological astuteness. But still it seems to have been a good glass, though under-polished; and they made it sometimes bear a power (a reputed power at least, which is often a very different matter) of 1128 even upon Venus; and the consent of several observers seems to confirm in full the accuracy of Bianchini's drawings. They claim no less than 11,800 micrometrical measures, and certainly appear to have taken a great deal of pains. If Schröter, half a century earlier, had, like most other people, made out little of these shadows, he established a mountainous and irregular terminator,' or boundary line of light and darkness, an atmosphere denser than our own, and a day and night of similar length to what we know. Sir W. Herschel, less successful, attacked him with an asperity which (pace tanti viri) seems to betray a slight tinge of personal feeling; Schröter replied. in the Philosophical Transactions for 1795, with much courtesy and firmness. We examined this controversy pretty carefully some years ago, and the result was entirely in favour of the astronomer of Lilienthal. Some of his discoveries, especially the differing aspect of the horns of the crescent, and their rapid variation in thickness and

sharpness, have since been verified by Mädler. May we not look to Dawes, armed with Alvan Clark's 84-inch beautiful object-glass and clock-work movement, for the rest

and more? But we fear that no one will give us any very good explanation for Arago's negative visibility' cannot be called an explanation of the curious but undoubted fact, that the unilluminated part of this planet is sometimes visible, and has been seen even in broad daylight. We can readily account for this appearance, this 'ash-light,' on the moon, which has the earth's broad face shining upon it; but that light must be quite inconsiderable at the distance of Venus; and there is nothing else to shine upon her. She may, perhaps, be phosphorescent a quality possessed but in a faint degree by terrestrial materials, though more generally so than might be supposed, as Mr. Wilson long ago proved by his experiments in a thoroughly darkened chamber,-but there this quality must be supposed to be developed in a much fuller degree. But what of the satellite of Venus? That is a very curious story, pretty nearly as mysterious in its way as the tale of Casper Hauser, and it deserves bringing into notice; but we have no room for it now

fugit irreparabile tempus Singula dum capti circumvectamur amore.

We must return homewards. How happy should we deem ourselves if, in so doing, we could only get one fair view of the back of the moon, and test Hansen's ingenious conjecture, built on a deep refinement of mathematical theory, that, in consequence of a slight but appreciable difference between its centre of figure and its centre of gravity, somewhat displaced by the neighbourhood of the earth, its other side may be destitute of neither water nor air, and not incapable of sustaining inhabitants like ourselves. But this we shall never be permitted to know, at least in this life. We must content ourselves with what we can see, and that truly is enough to excite

a lifelong wonder. No need either, in order to appreciate it, of the colossal 15-inch object-glasses of Merz at Poulkova under the autocratic eagle, or at Harvard University under 'the stars and stripes,' or of Lassell's exquisite 2-feet specula, so wonderfully finished, with a previous certainty of success, by means of a polisher of nothing but deal coated with pitch; or of the 4-feet mirror he is finishing, or perhaps has finished; or of De la Rue's of 13 inches in diameter, smaller indeed, but, as we can testify, admirably perfect. Bad indeed must be the instrument that fails us here, and worse than Galileo's early effort the little seed from which such a countless harvest of optic tubes has sprung. The one we are supposed to be using will astonish us by its revelations; and indeed its amount of light will be wearisome to a feeble eye. What a chaos of explosive action lies before us!-a surface blown up in literally many thousands of places, from the smallest pits which just dot the surface in our great telescopes, to the broad volcanic lakes, whose flattened interiors are as big as whole English counties, and are encompassed by stupendous girdles of ridges and peaks which might stand in proud rivalry among the Apennines or Pyrenees, nay, which sometimes overpass the loftiest Alpine summits. In point of dimensions, nothing on earth is to be named with these wonderful cavities, though their analogy with some of our own volcanic districts has been repeatedly pointed out, and of late beautifully exhibited by Professor Piazzi Smyth in his most interesting publication on the Peak of Teyde, more commonly known as Teneriffe. Others, again, of the lunar elevations, though possibly due to a similar eruptive or extrusive agency, are equally astonishing in their rectilinear extent. It is a glorious thing to wander in the mountain solitudes of our own planet; nevertheless he who has stood in the pine-forest at the edge of the Plateau des Bioux Artigues and looked up to the cloven crest

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of the mighty Pic du Midi d'Ossau, or has traversed the Great Scheidegg and the Wengern Alp beneath the shadow of the almost vertical steeps of the Wetterhorn and the Eiger, can form but a very feeble idea, either as to height or extent, of the precipices of the Lunar Apennines. Nor is the cleft of Lauterbrunnen, wonderful as is its aspect, especially in the descent from the Wengern Alp, more than a miniature of that wedge-shaped valley of the Lunar Alps, which was first figured by Bianchini, and which every observer of our satellite has seen, or ought to have seen a very different thing by the way-the old apologue ' eyes and no eyes' being not limited in its application to the days of youth. In fact, with a few resembling features, the general arrangement of the lunar surface is much contrasted with that of the earth. Though our steppes and prairies are well represented by the broad grey plains, we have but little that corresponds either in character or extent with the wonderful circular configuration into which so large a portion of the moon is thrown; and the cracks or furrows which intersect such extensive regions are still more dissimilar to anything except the artificial features of our globe: on the other hand, all the beautiful variety introduced by water in its different forms and positions seems there to be wholly unknown. What a pity it was that the keen eye of Gruithuisen was so illmatched with a wild imagination! More of his lunar discoveries were verified by other observers even at the time than might have been supposed from the subsequent evanescence of his fame; and more, we suspect, may still be recovered by those who will take the necessary pains. His predecessor Schröter, less lynx-eyed, was far more trustworthy; and his painstaking and honest labours, exhibited in two thick quarto volumes half made up of very ill-engraved designs, may still be consulted, we are of opinion, with more advantage than has been admitted by the highest lunar authorities, Beer

and Mädler. Nevertheless, though their work may be a little biassed by the desire of originality, it is a wonderful instance, together with the splendid 3-feet map of which it is the counterpart, of diligence, perseverance, and accuracy. Lohrmann's plates, published somewhat earlier, seem patterns of unsightly fidelity in a conventional style. His undertaking, unfortunately left incomplete from his failing vision, has, it is said, been recently completed by Schmidt, the well-known observer of the solar spots. But though very much has been accomplished, a separate and detailed examination of insulated regions recorded in large and oftenrepeated drawings -a 'Selenotopography' in short, as laborious as that of Schröter, but far more delicate and minute-is required before we can be said to know thoroughly the surface of the moon or can be in a position to draw secure conclusions. The 'Moon Committee' of the British Association are understood to have something of this kind in hand; and Nasmyth, the inventor of the celebrated steam-hammer, is said to be meditating great things with a reflector which collects as much light as the eye is well able to endure. Whoever undertakes any portion of this task ought selfevidently to be possessed of a certain amount of artistic talent, such as has been displayed, for instance, in the drawings of the 'Mare Crisium' by the Astronomer Royal for Scotland, Piazzi Smyth, published in the Edinburgh Transactions, or the designs will never prove very satisfactory. In the exceedingly curious department of Lunar Photography, Warren De la Rue stands altogether pre-eminent, and some of his inferences begin to be very fascinating. His hints as to the possibility of vegetation, and an atmosphere enveloping merely the lower regions of the moon, are original reproductions, if we may be allowed the expression, of Schröter's ideas derived through an entirely different channel, and deduced from actinic instead of

optical appearances. Our own impression is and it is not one deduced from investigations of yesterday that though the luminous eruptions of Sir W. Herschel, Captain Kater, and others, were mere illusions arising from reflected earth-light (about the vary. ing intensity of which, however, some mystery hangs), another generation will admit the continuance of the same explosive action which has so extensively modified the lunar globe as an unquestioned fact; its diminished manifestation, as compared with the terrific energy of earlier epochs, corresponding significantly with a similar decrease of volcanic activity on the earth. We have already referred to the researches of Piazzi Smyth at Teneriffe, so interesting in this point of view, and we must do so again, for that worthy son of a worthy father has produced one of the pleasantest books of modern days, as well as one of great scientific importance; nor should Mrs. P. Smyth's share of so adventurous an enterprise be passed by without the expression of due honour. In fact, the gentler sex have taken their part, if not extensively, yet uncommonly well, in astronomical labour. In early days honest (brav) Kirch,' as Olbers calls him, had his Maria Margareta to help him. The fame of Caroline Herschel deserves to be co-extensive with that of her illustrious brother;

Gloria, sideribus quam convenit esse

coævam,

Et tantum cœlo commoriente mori; and the aid that poor, weary, and worn-out Fallows received from his wife at the Cape of Good Hope ought never to be forgotten. But to return to Piazzi Smyth. While cordially advising the perusal of his Teneriffe, let us hope that the spirited author may yet have other opportunities of recording the results of his 'astronomer's experiment' above the clouds, and of again and again affording similar pleasure and interest to his readers.