that the only eclipse that could have been seen in that part of Asia Minor where the armies encountered, took place on the 28th of May, B.C. 584. Other instances of this kind might be cited, but we cannot afford our limited space for the multiplication of examples any further.

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The moon is the earth's only satellite. satellite in astronomical parlance is a small or secondary planet revolving round a larger or its primary, and forming thus a subordinate system in which the great solar system is, as it were, reproduced on a smaller scale; just as we see in organic life types of larger creations repeated in miniature reproductions. We apply the term only to our satellite because the earth is perhaps the only planet in the system that is graced with but a single satellite. The two planets nearest the sun, Mercury and Venus, have, however, none; and Mars, our nearest neighbour in the opposite direction, has none; but Jupiter has four, and Saturn eight. Of the remote members of our system, Uranus is supposed to have six, and Neptune probably two or more, though only one is established; but it seems highly probable, considering the increase of satellites corresponding with increased distance of the primary from the sun that we observe in the nearer planets, that Uranus and Neptune have many more; but the most powerful telescopes in existence are required to see those we have referred to, and if any smaller exist we can scarcely hope to detect them, for the planets themselves are smaller and fainter when viewed with the telescope than some of the satellites of Jupiter and Saturn. But what the earth lacks in number as regards satellitic accompaniment is made up by the magnitude of the one it does possess, for the moon is the largest satellite, compared to its primary, in the system, its diameter being one-fourth that of the earth, while Jupiter's moons range from a thirtieth to a fortieth of his diameter, and Saturn's are comparatively much less than these. The absolute diameter of the moon is about 2150 miles; its weight is sixty-nine trillions of tons, and its average distance from the earth 237,000 miles, so that the sixty-mile-an-hour train we made use of to express the sun's distance would run to the moon in about six months, and round it in a little over four days and a half. It revolves round the earth in 27 days, 7 hours, and 43 minutes, and in the course of this revolution presents us with the familiar aspects known as the phases. The cause of these phases is remarkably simple, yet the common explanations given of them are so complicated that we venture to devote a few lines to the

description of a simple experiment that will make the matter more understandable than pages of written explanation could do. Take in your hand a white or lightly-coloured ball, say a lightly-painted croquet ball, and place yourself at some distance from a lamp or the window of a room lighted by one window only. Hold the ball at arm's length between your eye and the light, and then your face, the ball, and the light will respectively represent the earth, moon, and sun. Now turn gently upon your heel, keeping your eye on the ball; when you have moved a few degrees round you will see a narrow line of light appear on the side of the ball nearest the lamp or window; this represents the crescent moon. Go on turning till you get just a quarter round, and the ball will appear as the moon at "first quarter;" still turn on, and it will present a gibbous" appearance, which will enlarge to "full moon" just when your back is turned to the light. By continuing your revolution the ball will re-pass through the gibbous phase to the last quarter, and so on till it comes just between you and the light, when, as it no longer will present any illuminated edge, it will represent "new moon." If you perform the experiment at night, with a lamp, and the ball, when between your eye and the lamp, hides the latter, you will have the best possible example of an eclipse of the sun, and if, when at "full moon," the shadow of your head falls upon the ball, you will reproduce an eclipse of the moon.

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Every one is familiar with the singular phenomenon known as the new moon carrying the old moon in her arms," when, in addition to the slender crescent, the whole disc is more or less distinctly visible, a few days after new moon; the same appearance, or "the old moon nursing the new," presents itself in like manner in the waning moon, when she rises a few hours before the sun, but we fear there are few who shake off dull sleep in time to see it. This is what is called the lumière cendrée, or ash-light of the moon. Its appearance used to be taken as an indication that the moon was phosphorescent, or possessed some light of her own independent of that she receives from the sun. Now, however, it is satisfactorily proved to arise from the sunlight reflected from the earth upon the dark room, for it must be remembered that the earth is to the moon what the moon is to the earth, a reflector of the sun's light, and that when it is new moon to the earth it is full earth to the moon, and vice versa, and thus the opaque moon becomes illuminated by earthlight-to use a term analogous to moonlight-but on account of the great size of the earth com

pared to the moon, this light is fourteen times as bright as our moonlight, and thus the occasional brilliancy of this "reflection of a reflection" is accounted for.

The moon, as we have said, revolves round the earth in about 27 days. The direction of this motion is contrary to that of the earth upon its axis, or the apparent motion of the sun, and hence the moon appears to be always lagging behind the sun, rising, as it does, about 50 minutes later every day. In just the same time that the moon occupies in revolving round the earth, she also rotates upon her own axis, and this is why we always behold the same face turned towards us. This seems like a paradox, but it is a demonstrable fact.

Some six or eight years ago, considerable discussion took place upon this subject in the columns of our public journals, and a number of "half-fledged savans," better able to comprehend theories of their own creation than those established by fact and demonstrated by experiment, endeavoured, in various ways, to prove that the moon does not rotate upon her axis, and even at the present time the argument is fiercely raging among a certain grade of philosophers. If any one has a lingering notion in favour of this non-rotatory theory we would suggest the performance of one of a vast number of simple experiments that completely disprove it, and at the same time explain the apparent paradox. Let the reader place himself before a round table with a ball or basin or any other object in its centre; let him suppose this central object represents the earth and himself the moon ; let him tie one end of a long string to his button-hole and fasten the other end to a chair, or any other object in the room, leaving plenty of space; then let him glide round the table, keeping his face towards the central object (as the moon keeps her face towards the earth), and by the time he has completed one revolution round the table he will find the string twisted round his body; here is proof positive that he rotated on his axis, or how else came the string around him? As a converse to this experiment let him repeat it, but this time keeping his face towards an opposite wall, or appearing to rotate to the object on the table: the string in this case will not be wound round him, because he has not rotated on his axis.

But while the moon's motion on her axis is uniform, her motion round the earth is not so; and this gives rise to an apparent wobbling motion which enables us to see sometimes a little more of one side of her face and sometimes a little more of the other; in this way,

instead of half, four-sevenths of the moon's surface is rendered visible to us. Of the remaining three-sevenths we inhabitants of this earth must remain ignorant to all eternity.

The proximity of our satellite, and the plenitude of objects it presents for observation, conspire to render it one of the most favourite and most striking telescopic objects in the whole universe, and even before the invention of the telescope intelligent views and suppositions were formed respecting the inequalities visible to the naked eye upon its surface. Plutarch, in a treatise "On the Face of the Moon," expresses an opinion that from the spots seen upon it might be surmised the existence of deep clefts, and valleys, and mountain summits" which cast long shadows like Mount Athos, whose shadow reaches to Lemnos." A more fanciful theorist of ancient times conceived the moon to be a mirror reflecting back an image of the forms and outlines of the continents and seas of the earth, and even in these days some such opinion seems to hold ground among some nations, for Humboldt tells us that, while showing the moon through a telescope to an accomplished Persian, he was astonished to hear him propound the same hypothesis as one generally accepted in his country.

"It is ourselves that we see in the moon," said the Persian, "that is the map of the earth."

Telescopic scrutiny reveals to us surface peculiarities wonderfully diversified in their configuration, for, besides the level plains that form the dusky spots visible without a telescope, we perceive extensive mountain ranges with their attendant valleys, huge isolated hills and masses of rock flanked by projecting crags and strewed round their bases with detached and unconnected fragments apparently broken from the parent mass, rents and ravines and yawning chasms, and, above all, the striking circular craters and volcanic formations that form the chief and most extraordinary element of the lunar scenery. Reviewing these in the order in which we have mentioned them, we have first to notice the extensive dusky spots. These, in consequence of their smooth appearance, were for a long time supposed to consist of water, and the ancient selenographers (this is the analogous term to geographer) gave them the appellations of seas and lakes, and distinguished them by designations derived from influences supposed to be exercised by the moon over meteorological and other natu ral phenomena: for instance, there is the Oceanus Procellarium, or ocean of storms, the largest of the so-called seas, covering a surface of 90,000 square miles; the Mare Tranquillitatis, or sea of tranquillity; the Sinus Iridum,

or bay of rainbows, and many others, covering, in the aggregate, about two-thirds of the visible hemisphere of the moon. The appellations of seas, &c., are still retained for convenience' sake in referring to these portions of the moon's disc; but the telescope has long ago determined that they cannot be bodies of water, for their surfaces are diversified with permanent undulations and irregularities, and are more or less covered with volcanic and other selenological peculiarities. They are mostly skirted by lofty chains of mountains, and some of them are variously tinted with colour; some with a greenish tinge, others red, and others slightly blue. These different tints are exceedingly enigmatical, and have been supposed to indicate the existence of something like vegetation covering these vast areas; but this idea is negatived when we bear in mind the fact, to which we shall have further occasion to allude, that the moon is destitute of such an atmosphere as would be required to sustain vegetable life. Since then we cannot suppose them to be seas or districts of fertility, we are driven to the conclusion that they are vast flats or tracts of level land, and, regarding the moon as having once been the scene of tremendous erruptive disturbances, we must assume these to represent the comparatively undisturbed regions of her surface.

Passing from the plains to the mountainous regions, we remark that the lunar mountain chains present a strong family likeness to those of the earth, and doubtless owe their origin to the workings of the same cause acting upon similar materials, but under different conditions. A striking feature in all the mountainous formations of the moon is their enormous height relatively to the moon's diameter, for in this respect they greatly exceed in magnitude the mountains of the earth.

We may

here mention incidentally, that if a globe two feet in diameter were taken to represent the earth, the highest earthly mountain would be justly represented by a grain of sand laid upon that globe's surface. The highest of the earth's mountains attains an altitude of about 28,000 feet, and the highest of those on the moon about 25,000: but considering the diameter of the moon is only a fourth of that of the earth, it follows that the lunar mountains are thus comparatively four times higher than ours. Near the moon's south pole some of these lofty mountain summits glitter in perpetual sunlight, "eternal sunshine" literally "settles on their heads ;" but in striking contrast to these there are in their neighbourhood immense cavities into which the sun's rays never penetrate, and which are thus shrouded in perpetual darkness. The

most remarkable of the lunar mountain chains are named after those of the earth, as the Alps, Apennines, Caucasus, and Carpathians. The first of these is the most extensive, and may be detected with the naked eye when the moon is about half-full; it is suspected that the ancients from this fact derived their notion that the moon was covered with mountains and valleys. In addition to these chains and ridges there exists on the moon every phase of mountain character that we find on the earth down to isolated peaks (with which, however, we have but few in common on the earth) that shoot from the plains like gigantic sugar-loaves several thousand feet in height, and seem to have been protruded through the surface by some sudden internal force just as a needle would be driven through a sheet of paper.

But we pass thus cursorily over these less peculiar features that we may dwell the longer and devote the more space to the consideration of the most interesting and important characteristics of the lunar surface, the striking circular formations known as the Ring Mountains. We are anxious to devote a little extra attention to this branch of our subject, because the explanations and illustrations we shall have occasion to offer are not to be found in even the more elaborate treatises purporting to give information upon this branch of celestial physics, and because the scrutiny of these annular mountains affords us a most interesting insight into the moon's physical history; and, inasmuch as the history of a satellite is doubtless typical of that of its primary, we may perhaps safely tread the field of conjecture, and from the moon's history infer the probable cosmical origin of our own globe.

The Ring Mountains are of so strikingly

type of the whole family of them. They almost always consist of a circular rampart or mountainous amphitheatre more or less perfect in its structure, and with an isolated peak or mountain in the centre. But while their form can be so generally described, their individual appearances present many modifications; sometimes the central peak is wanting, sometimes the circular wall is in great part broken away and imperfect; sometimes the enclosed area takes the form of a level plain or plateau, at others it is hollowed out into a hemispherical cavity or vast cup, of which the rampart forms the brim. In size they vary from 30 or 40 miles in diameter down to a magnitude so small as to require the highest telescopic power to discern them. In numbers they are countless, the small ones being sometimes so thickly grouped together as to present an appearance like solidified froth. The altitude of the circular rampart and central peak varies like other lunar mountains from twenty thousand to a few feet in height.

We are enabled, through the kindness of Mr. Nasmyth (to whose lunar researches we shall presently

compared to the whole surface of the moon, this would be proportional to a square inch on a globe about a foot in diameter. These mountains are distinguished by the names of celebrities of all ages in science and literature: our drawing includes those named after Maurolycus, Cuvier, Clairaut, and Stöffler; but the reader doubtless will not care to be informed which is which. This nomenclature is open to considerable objections, for lately some hitherto unnamed mountains have been christened with names that will certainly be forgotten twenty years hence, and so when in

more fully allude) to give a representation as accurate as skilful engraving can make it of a portion of the lunar surface, showing in a highly satisfactory manner the aspect of a region most thickly covered with these peculiar formations.*

The space included in this illustration represents an area of about 30,000 square miles;

We have not attempted to give an illustration of the whole disc of the moon, for the obvious reason that it is totally impossible, within the compass of a few inches, to give any but a grossly deceitful idea of the configuration of its surface. The splotchy productions generally put forth in popular treatises on this subject bear no more resemblance to the reality than would the segment of a Stilton cheese.

future times some really great names require a niche in this lunar temple, there will be no room for them. "The neutral ground of mythology and classic antiquity," says Herschel, "would have been the safest foundation for a system of nomenclature, and we may hope that at some future survey of the moon some such will be adopted." A striking feature in our illustration will doubtless have arrested the reader's attention; we allude to the intensely black shadows that shroud a portion of the details of the picture. This is a

consequence of the absence of a lunar atmosphere.

Daylight, or diffused light distinguished from the glaring sunshine on the earth, is produced by the reflection of the sun's rays from the earth's atmosphere, and thus it is that light pervades places where no sun shines; but nothing of this kind is seen on the moon; those parts of her surface that catch the direct rays of the sun shine with a dazzling brilliancy like frosted silver; but where no direct sunshine falls there is no light, but a region of pitchy darkness.

J. CARPENTER.