CHAPTER VII.

TOPOGRAPHY OF THE MOON.

It is scarcely necessary to seek the reasons which prompted astronomers, soon after the invention of the telescope, to map the surface features of the moon. They may have considered it desirable to record the positions of the spots upon her disc, for the purpose of facilitating observations of the passage of the earth’s shadow over them in lunar eclipses; or they may have been actuated by a desire to register appearances then existing, in order that if changes took place in after years these might be readily detected. Scheiner was one of the earliest of lunar cartographers; he worked about the middle of the seventeenth century; but his delineations were very rough and exaggerated. Better maps—the best of the time, according to an old authority—were engraved by one Mellan, about the years 1634 or 1635. At about the same epoch, Langreen and Hevelius were working upon the same subject. Langreen executed some thirty maps of portions of the moon, and introduced the practice of naming the spots after philosophers and eminent men. Hevelius spent several years upon his task, the results of which he published in a bulky volume containing some 50 maps of the moon in various phases, and accompanied by 500 pages of letter-press. He rejected Langreen’s system of nomenclature, and called the spots after the seas and continents of the earth to which he conceived they bore resemblance. Riccioli, another selenographer, whose map was compiled from observations made by Grimaldi, restored Langreen’s nomenclature, but he confined himself to the names of eminent astronomers, and his system has gained the adhesion of the map-makers of later times. Cassini prepared a large map from his own observations, and it was engraved about the year 1692. It appears to have been regarded as a standard work, for a reduced copy of it was repeatedly issued with the yearly volumes of the _Connaissance des Temps_, (the “Nautical Almanac” of France) some time after its publication. These small copies have no great merit: the large copper plate of the original was, we are told by Arago, who received the statement from Bouvard, sold to a brazier by a director of the French Government Printing-Office, who thought proper to disembarrass the stores of that establishment, by ridding them of what he considered lumber! La Hire, Mayer, and Lambert, followed during the succeeding century, in this branch of astronomical delineation. At the commencement of the present century, the subject was very earnestly taken up by the indefatigable Schroeter, who, although he does not appear to have produced a complete map, produced a topograph of the moon in a large series of partial maps and drawings of special features. Schroeter was a fine observer, but his delineations show him to have been an indifferent draughtsman. Some of his drawings are but the rudest representations of the objects he intended to depict; many of the bolder features of conspicuous objects are scarcely recognizable in them. A bad artist is as likely to mislead posterity as a bad historian, and it cannot be surprising if observers of this or future generations, accepting Schroeter’s drawings as faithful representations, should infer from them remarkable changes in the lunar details. It is much to be regretted that Schroeter’s work should be thus depreciated. Lohrman of Dresden, was the next cartographer of the moon; in 1824 he put forth a small but very excellent map of 15 inches diameter, and published a book of descriptive text, accompanied by sectional charts of particular areas. His work, however, was eclipsed by the great one which we owe to the joint energy of MM. Beer and Maedler, and which represents a stupendous amount of observing work carried on during several years prior to 1836, the date of their publication. The long and patient labour bestowed upon their map and upon the measures on which it depends, deserve the highest praise which those conversant with the subject can bestow, and it must be very long before their efforts can be superseded.

Beer and Maedler’s map has a diameter of 37 inches: it represents the phase of the moon visible in the condition of mean libration. The details were charted by a careful process of triangulation. The disc was first divided into “triangles of the first order,” the points of which (conspicuous craters) were accurately laid down by reference to the edges of the disc: one hundred and seventy-six of these triangles, plotted accurately upon an orthographic projection of the hemisphere, formed the reliable basis for their charting work. From these a great number of “points of the second order” were laid down, by measuring their distance and angle of position with regard to points first established. The skeleton map thus obtained was filled up by drawings made at the telescope: the diameters of the measureable craters being determined by the micrometer.

Beer and Maedler also measured the heights of one thousand and ninety-five lunar mountains and crater-summits: the resulting measures are given in a table contained in the comprehensive text-book which accompanies their map. These heights are found by one of two methods, either by measuring the length of the shadow which the object casts under a known elevation of the sun above its horizon, or by measuring the distance between the illuminated point of the mountain and the “terminator” in the following manner. In the annexed figure (Fig. 15) let the circle represent the moon and M a mountain upon it: let S A be the line of direction of the sun’s rays, passing the normal surface of the moon at A and just tipping the mountain top. A will be the terminator, and there will be darkness between it and the star-like mountain summit M. The distance between A and M is measured: the distance A B is known, for it is the moon’s radius. And since the line S M is a tangent to the circle the angle B A M is a right angle. We know the length of its two sides AB, AM, and we can therefore by the known properties of the right-angled triangle find the length of the hypothenuse BM: and since BM is made up of the radius BA plus the mountain height, we have only to subtract the moon’s radius from the ascertained whole length of the hypothenuse and we have the height of the mountain. MM. Beer and Maedler exhibited their measures in French toises: in the heights we shall have occasion to quote, these have been turned into English feet, upon the assumption that the toise is equal to 6·39 English feet. The nomenclature of lunar features adopted by Beer and Maedler is that introduced by Riccioli: mountains and features hitherto undistinguished were named by them after ancient and modern philosophers, in continuance of Riccioli’s system, and occasionally after terrestrial features. Some minute objects in the neighbourhood of large and named ones were included under the name of the large one and distinguished by Greek or Roman letters.

The excellent map resulting from the arduous labours of these astronomers is simply a map: it does not pretend to be a picture. The asperities and depressions are symbolized by a conventional system of shading and no attempt is made to exhibit objects as they actually appear in the telescope. A casual observer comparing details on the map with the same details on the moon itself would fail to identify or recognize them except where the features are very conspicuous. Such an observer would be struck by the shadows by which the lunar objects reveal themselves: he would get to know them mostly by their shadows, since it is mainly by those that their forms are revealed to a terrestrial observer. But such a map as that under notice indicates no shadows, and objects have to be identified upon it rather by their positions with regard to one another or to the borders of the moon than by any notable features they actually present to view. This inconvenience occurred to us in our early use of Beer and Maedler’s chart, and we were induced to prepare for ourselves a map in which every object is shown somewhat, if imperfectly, as it actually appears at some period of a lunation. This was done by copying Beer and Maedler’s outlines and filling them up by appropriate shading. To do justice to our task we enlarged our map to a diameter of six feet. Upon a circle of this diameter the positions and dimensions of all objects were laid down from the German original. Then from our own observations we depicted the general aspect of each object: and we so adjusted the shading that all objects should be shown under about the same angle of illumination—a condition which is never fulfilled upon the moon itself, but which we consider ourselves justified in exhibiting for the purpose of conveying a fair impression of how the various lunar objects actually appear at some one or other part of a lunation.

The picture-map thus produced has been photographed to the size convenient for this work: and in order to make it available for the identification of such objects as we may have occasion to refer to, we have placed around it a co-ordinate scale of arbitrary divisions by which any object can be found as by the latitude and longitude divisions upon a common geographical map. We have also prepared a skeleton map which includes the more conspicuous objects, and which faces the picture map (Plates IV. and V.) The numbers on the skeleton map are those given in the second column of the accompanying table. The table also gives the co-ordinate positions of the various craters, the names of which are, for convenience of reference, printed in alphabetical order.

Name. Number. Map Ordinates.

Abulfeda 107 30·0 120·7 Agrippa 151 31·2 110·0 Airy 93 34·7 123·0 Albategnius 109 35·5 119·7 Aliacensis 61 35·8 131·0 Almanon 94 29·0 122·3 Alpetragius 92 40·8 122·4 Alphonsus 110 39·6 120·9 Apianus 62 33·6 129·3 Apollonius 154 6·5 109·5 Arago 152 24·7 108·7 Archimedes 191 40·3 95·8 Aristarchus 176 62·3 99·2 Aristillus 190 37·0 93·3 Aristotle 209 30·0 84·6 Arzachael 84 39·5 124·0 Atlas 228 20·7 86·6 Autolycus 189 36·8 95·5 Azophi 76 30·7 126·8 Bacon 17 32·5 142·0 Baily 207 26·0 85·4 Barocius 34 31·8 138·5 Bessel 179 27·4 100·1 Bettinus 11 48·8 144·9 Bianchini 215 51·6 86·3 Billy 121 64·3 121·4 Blancanus 12 43·7 144·8 Bonpland 110 48·5 117·6 Borda 56 15·2 131·0 Boscovich 160 31·1 106·8 Bouvard 40 66·6 134·3 Briggs 196 68·0 97·2 Bullialdus 86 50·1 125·5 Burg 206 25·5 87·5 Calippus 199 32·4 90·3 Campanus 71 52·3 129·0 Capella 104 17·8 118·0 Capuanus 43 50·5 132·8 Casatus 7 43·7 147·0 Cassini 200 35·5 89·7 Catherina 95 24·7 124·0 Cavalerius 144 71·2 109·5 Cavendish 88 63·5 127·4 Cichus 44 47·3 132·8 Clavius 13 41·8 143·5 Cleomides 183 10·7 97·0 Colombo 98 12·8 122·7 Condamine 214 48·7 84·2 Condorcet 164 4·5 104·7 Copernicus 147 49·8 107·0 Cyrillus 96 23·5 121·3 Damoiseau 124 69·2 117·2 Davy 113 43·2 119·8 Deambrel 129 26·8 113·5 Delisle 195 55·7 95·2 Descartes 106 28·5 119·3 Diophantus 194 55·5 96·3 Doppelmayer 70 58·6 129·6 Encke 140 59·7 110·6 Endymion 227 20·6 83·8 Epigenes 223 39·0 79·5 Erastothenes 168 44·6 104·0 Eudoxus 208 29·7 88·0 Fabricius 35 20·0 136·8 Fernelius 37 35·1 134·8 Firmicus 156 5·8 107·7 Flamsteed 126 62·8 114·5 Fontana 122 65·9 123·0 Fontenelle 221 43·0 81·3 Fourier 67 62·5 130·7 Fracastorius 78 20·5 127·0 Furnerius 52 11·7 133·0 Gambart 138 47·2 112·2 Gartner 224 26·5 82·3 Gassendi 90 59·7 123·3 Gauricus 46 43·5 132·5 Gauss 201 10·3 90·3 Gay Lussac 169 50·1 103·8 Geber 83 29·6 124·8 Geminus 187 13·0 93·0 Gérard 218 63·7 88·8 Goclenius 101 11·8 118·5 Godin 135 31·3 111·7 Grimaldi 125 70·8 116·3 Gruemberger 6 41·4 145·8 Gueriké 114 46·5 119·6 Guttemberg 102 13·9 118·3 Inghirami 27 61·3 138·9 Isidorus 103 16·7 118·0 Kant 105 25·8 118·5 Kepler 146 60·0 108·0 Kies 72 49·7 128·8 Kircher 10 47·5 145·8 Klaproth 8 43·5 146·7 La Caille 74 37·5 126·8 Lagrange 68 67·0 131·3 La Hire 177 54·3 99·3 Lalande 117 43·4 115·3 Lambert 193 49·6 97·8 Landsberg 127 54·0 113·0 Langreen 100 6·3 117·7 Letronne 120 62·0 119·0 Licetus 21 34·1 139·6 Lichtenberg 197 66·5 94·9 Linnæus 188 31·7 95·7 Littrow 185 20·5 99·4 Lohrman 143 71·3 112·8 Longomontanus 23 45·7 140·6 Lubiniezky 91 51·3 123·5 Macrobius 182 13·7 100·2 Maginus 22 40·0 140·4 Mairan 217 56·7 89·5 Manilius 167 32·2 103·9 Manzinus 4 31·3 146·0 Maraldi 181 18·6 100·8 Marius 171 65·0 105·5 Maskelyne 132 19·5 111·0 Mason 204 23·7 88·8 Maupertius 213 48·7 85·8 Maurolycus 33 31·8 137·0 Menelaus 165 28·3 103·0 Mercator 65 51·4 130·2 Mersenius 89 61·7 125·7 Messala 202 14·0 90·5 Messier 131 10·8 114·0 Metius 36 18·8 105·9 Moretus 5 39·5 146·5 Moesting 128 41·6 113·2 Neander 57 18·7 131·0 Nearchus 18 26·8 142·0 Newton 1 41·0 147·7 Nonius 49 36·5 133·2 Olbers 172 73·0 107·7 Pallas 149 38·6 109·5 Parrot 108 35·8 121·6 Petavius 80 9·5 127·5 Phocylides 25 55·5 141·6 Piazzi 41 65·0 133·5 Picard 163 8·3 104·7 Piccolomini 58 21·7 131·0 Pico 211 41·9 87·3 Pitatus 63 44·1 130·2 Plana 205 24·8 88·8 Plato 210 41·8 84·8 Playfair 75 33·5 127·5 Pliny 165 24·2 103·4 Poisson 60 32·8 131·0 Polybius 82 24·5 125·6 Pontanus 59 29·0 130·2 Posidonius 186 22·2 94·3 Proclus 162 11·4 104·5 Ptolemy 111 39·5 118·2 Purbach 73 38·7 128·4 Pythagoras 220 53·0 81·2 Pytheas 178 49·7 100·4 Ramsden 42 52·9 132·5 Reamur 118 37·3 114·6 Reiner 145 67·3 108·5 Reinhold 139 51·5 111·2 Repsold 219 60·2 85·7 Rheita 51 16·1 134·2 Riccioli 142 72·7 113·8 Riccius 50 23·7 133·5 Ritter 134 26·0 111·6 Roemer 184 18·3 97·6 Ross 161 25·0 105·3 Sabine 133 25·0 112·0 Sacrobosco 77 27·5 127·7 Santbech 79 15·7 126·8 Saussure 31 39·6 137·7 Scheiner 14 45·5 143·5 Schickard 28 59·0 137·5 Schiller 24 51·3 141·0 Schroeter 137 42·3 110·7 Schubert 155 2·3 110·8 Segner 16 51·3 143·5 Seleucus 174 69·0 99·8 Sharp 216 54·2 87·7 Short 2 39·7 147·4 Silberschlag 157 32·0 108·1 Simpelius 3 35·8 147·7 Snell 55 11·3 129·6 Soemmering 136 42·8 112·2 Stadius 148 45·6 107·0 Stevinus 53 11·9 130·7 Stoefler 32 35·6 136·8 Strabo 226 23·2 81·6 Struve 203 18·3 88·7 Taruntius 153 11·7 109·0 Taylor 130 27·6 116·2 Thales 225 24·3 81·8 Thebit 85 40·8 126·8 Theophilus 97 22·3 120·0 Timæus 222 38·3 80·8 Timocharis 192 45·1 97·0 Tobias Mayer 170 54·5 103·0 Triesnecker 150 35·5 109·8 Tycho 30 43·0 142·3 Ukert 159 37·1 107·5 Vasco de Gama 173 72·8 104·9 Vendelinus 99 6·8 121·6 Vieta 69 64·3 129·7 Vitello 66 55·8 130·7 Vitruvius 180 20·1 102·0 Vlacq 19 25·0 140·1 Zuchius 15 50·7 144·2

The strong family likeness pervading the craters of the moon renders it unnecessary that we should attempt a description of each one of them or even of one in twenty. We have, however, thought that a few remarks upon the salient features of a few of the most important may be acceptable in explanation of our illustrative plates; and what we have to say of the few may be taken as representative of the many.

COPERNICUS, 147—(49·8—107·0). Plate VIII.

This may deservedly be considered as one of the grandest and most instructive of lunar craters. Although its vast diameter (46 miles) is exceeded by others, yet, taken as a whole, it forms one of the most impressive and interesting objects of its class. Its situation, near the centre of the lunar disc, renders all its wonderful details, as well as those of its immediately surrounding objects, so conspicuous as to establish it as a very favourite object. Its vast rampart rises to upwards of 12,000 feet above the level of the plateau, nearly in the centre of which stands a magnificent group of cones, three of them attaining the height of upwards of 2400 feet.

The rampart is divided by concentric segmental terraced ridges, which present every appearance of being enormous landslips, resulting from the crushing of their over-loaded summits, which have slid down in vast segments and scattered their débris on to the plateau. Corresponding vacancies in the rampart may be observed from whence these prodigious masses have broken away. The same may be noticed, although in a somewhat modified degree, around the exterior of the rampart. In order to approach a realization of the sublimity and grandeur of this magnificent example of a lunar volcanic crater, our reader would do well to endeavour to fix his attention on its enormous magnitude and attempt to establish in his mind’s eye a correct conception of the scale of its details as well as its general dimensions, which, as they so prodigiously transcend those of the largest terrestrial volcanic craters, require that our ideas as to magnitude of such objects should be, so to speak, educated upon a special standard. It is for this reason we are anxious our reader, when examining our illustrations, should constantly refer the objects represented in them to the scale of miles appended to each plate, otherwise a just and true conception of the grandeur of the objects will escape him.

Copernicus is specially interesting, as being evidently the result of a vast discharge of molten matter which has been ejected at the focus or centre of disruption of an extensively upheaved portion of the lunar crust. A careful examination of the crater and the district around it, even to the distance of more than 100 miles on every side, will supply unmistakable evidence of the vast extent and force of the original disruption, manifested by a wonderfully complex reticulation of bright streaks which diverge in every direction from the crater as their common centre. These streaks do not appear on our plate, nor are they seen upon the moon except at and near the full phase. They show conspicuously, however, by their united lustre on the full moon, Plate III. Every one of those bright streaks, we conceive, is a record of what was originally a crack or chasm in the solid crust of the moon, resulting from some vastly powerful upheaving agency over the site of whose focus of energy Copernicus stands. The cracking of the crust must have been followed by the ejection of subjacent molten matter up through the reticulated cracks; this, spreading somewhat on either side of them, has left these bright streaks as a visible record of the force and extent of the upheaval; while at the focus of disruption from whence the cracks diverge, the grand outburst appears to have taken place, leaving Copernicus as its record and result.

Many somewhat radial ridges or spurs may be observed leading away from the exterior banks of the great rampart. These appear to be due to the more free egress which the extruded matter would find near the focus of disruption. The spur-ridges may be traced fining away for fully 100 miles on all sides, until they become such delicate objects as to approach invisibility. Several vast open chasms or cracks may be observed around the exterior of the rampart. They appear to be due to some action subsequent to the formation of the great crater—probably the result of contraction on the cooling of the crust, or of a deep-seated upheaval long subsequent to that which resulted in the formation of Copernicus itself, as they intersect objects of evidently prior formation.

Under circumstances specially favourable for “fine vision,” for upwards of 70 miles on all sides around Copernicus, myriads of comparatively minute but perfectly-formed craters may be observed. The district on the south-east side is specially rich in these wonderfully thickly-scattered craters, which we have reason to suppose stand over or upon the reticulated bright streaks; but, as the circumstances of illumination which are requisite to enable us to detect the minute craters are widely adverse to those which render the bright streaks visible, namely, nearly full moon for the one and gibbous for the other, it is next to impossible to establish the fact of coincidence of the sites of the two by actual simultaneous observation.

At the east side of the rampart, multitudes of these comparatively minute craters may also be detected, although not so closely crowded together as those on the west side; but among those on the east may be seen myriads of minute prominences roughening the surface; on close scrutiny these are seen to be small mounds of extruded matter which, not having been ejected with sufficient energy to cause the erupted material to assume the crater form around the vent of ejection, have simply assumed the mound form so well known to be the result of volcanic ejection of moderate force.

Were we to select a comparatively limited portion of the lunar surface abounding in the most unmistakable evidence of volcanic action in every variety that can characterize its several phases, we could not choose one yielding in all respects such instructive examples as Copernicus and its immediate surroundings.

GASSENDI, 90—(59·7—123·3). Frontispiece.

An interesting crater about 54 miles diameter; the height of the most elevated portion of the surrounding wall from the plateau being about 9600 feet. The centre is occupied by a group of conical mountains, three of which are most conspicuous objects and rise to nearly 7000 feet above the level of the plateau. As in other similar cases, these central mountains are doubtless the result of the expiring effort of the eruption which had formed the great circular wall of the crater. The plateau is traversed by several deep cracks or chasms nearly one mile wide.

Both the interior and exterior of the wall of the crater are terraced with the usual segmental ridges or landslips. A remarkable detached portion of the interior bank is to be seen on the east side, while on the west exterior of the wall may be seen an equally remarkable example of an outburst of lava subsequent to the formation of the wall or bank of the crater; it is of conical form and cannot fail to secure the attention of a careful observer.

Interpolated on the north wall of the crater may be seen a crater of about 18 miles diameter which has burst its bank in towards the great crater, upon whose plateau the lava appears to have discharged itself.

The neighbourhood of Gassendi is diversified by a vast number of mounds and long ridges of exudated matter, and also traversed by enormous chasms and cracks, several of which exceed one mile wide and are fully 100 miles in length, and, as is usual with such cracks, traverse plain and mountain alike, disregarding all surface inequalities.

Numbers of small craters are scattered around; the whole forming an interesting and instructive portion of the lunar surface.

EUDOXUS, 208 (29·7—88·0), and ARISTOTLE, 209 (30·0—84·6). Plate X.

Two gigantic craters, Eudoxus being nearly 35 miles in diameter and upwards of 11,000 feet deep, while Aristotle is about 48 miles in diameter, and about 10,000 feet deep (measuring from the summit of the rampart to the plateau). These two magnificent craters present all the true volcanic characteristics in a remarkable degree. The outsides as well as the insides of their vast surrounding walls or banks display on the grandest scale the landslip feature, the result of the over-piling of the ejected material, and the consequent crushing down and crumbling of the substructure. The true eruptive character of the action which formed the craters is well evinced by the existence of the groups of conical mountains which occupy the centres of their circular plateaux, since these conical mountains, there can be little doubt, stand over what were once the vents from whence the ejected matter of the craters was discharged.

On the west side of these grand craters may be seen myriads of comparatively minute ones (we use the expression “comparatively minute,” although most of them are fully a mile in diameter). So thickly are these small craters crowded together, that counting them is totally out of the question; in our original notes we have termed them “Froth craters” as the most characteristic description of their aspect.

The exterior banks of Aristotle are characterized by radial ridges or spurs: these are most probably the result of the flowing down of great currents of very fluid lava. To the east of the craters some very lofty mountains of exudation may be seen, and immediately beyond them an extensive district of smaller mountains of the same class, so thickly crowded together as under favourable illumination to present a multitude of brilliant points of light contrasted by intervening deep shade. On the west bank of Aristotle a very perfect crater may be seen, 27 miles in diameter, having all the usual characteristic features.

About 40 miles to the east of Eudoxus there is a fine example of a crack or fissure extending fully 50 miles—30 miles through a plain, and the remaining 20 miles cutting through a group of very lofty mountains. This great crack is worthy of attention, as giving evidence of the deep-seated nature of the force which occasioned it, inasmuch as it disregards all surface impediments, traversing plain and group of mountains alike.

There are several other features in and around these two magnificent craters well worthy of careful observation and scrutiny, all of them excellent types of their respective classes.

TRIESNEKER, 150 (35·5—109·8). Plate XI.

A fine example of a normal lunar volcanic crater, having all the usual characteristic features in great perfection. Its diameter is about 20 miles, and it possesses a good example of the central cone and also of interior terracing.

The most notable feature, however, in connection with this crater, and on account of which we have chosen it as a subject for one of our illustrations, is the very remarkable display of chasms or cracks which may be seen to the west side of it. Several of these great cracks obviously diverge from a small crater near the west external bank of the great one, and they subdivide or branch out, as they extend from the apparent point of divergence, while they are crossed or intersected by others. These cracks or chasms (for their width merits the latter appellation) are nearly one mile broad at the widest part, and after extending to fully 100 miles, taper away till they become invisible. Although they are not test objects of the highest order of difficulty, yet to see them with perfect distinctness requires an instrument of some perfection and all the conditions of good vision. When such are present, a keen and practised eye will find many details to rivet its attention, among which are certain portions of the edges of these cracks or chasms which have fallen in and caused interruptions to their continuity.

THEOPHILUS, 97 (22·3—120·0). CYRILLUS, 96 (23·5—121·3). CATHARINA, 95 (24·7—124·0). Plate XII.

These three magnificent craters form a very conspicuous group near the middle of the south-east quarter of the lunar disc.

Their respective diameters and depths are as follows:—

Theophilus, 64 miles diameter; depth of plateau from summit of crater wall, 16,000 feet; central cone, 5200 feet high.

Cyrillus, 60 miles diameter; depth of plateau from summit of crater wall, 15,000 feet; central cone, 5800 feet high.

Catharina, 65 miles diameter; depth of plateau from summit of crater wall, 13,000 feet; centre of plateau occupied by a confused group of minor craters and débris.

Each of these three grand craters is full of interesting details, presenting in every variety the characteristic features which so fascinate the attention of the careful observer of the moon’s wonderful surface, and affording unmistakable evidence of the tremendous energy of the volcanic forces which at some inconceivably remote period piled up such gigantic formations.

Theophilus by its intrusion within the area of Cyrillus shows in a very striking manner that it is of comparatively more recent formation than the latter crater. There are many such examples in other parts of the lunar disc, but few of so very distinct and marked a character.

The flanks or exterior banks of Theophilus, especially those on the west side, are studded with apparently minute craters, all of which when carefully scrutinized are found to be of the true volcanic type of structure; and minute as they are, by comparison, they would to a beholder close to them appear as very imposing objects; but so gigantic are the more notable craters in the neighbourhood, that we are apt to overlook what are in themselves really large objects. It is only by duly training the mind, as we have previously urged, so as ever to keep before us the vast scale on which the volcanic formations of the lunar surface are displayed, that we can do them the justice which their intrinsic grandeur demands. We trust that our illustrations may in some measure tend to educate the mind’s eye, so as to derive to the full the tranquil enjoyment which results from the study of the manifestation of one of the Creator’s most potent agencies in dealing with the materials of his worlds, namely, volcanic force. So rich in wonderful features and characteristic details is this magnificent group and its neighbourhood, that a volume might be filled in the attempt to do justice, by description, to objects so full of suggestive subject for study.

THEBIT, 85—(40·8—126·8).

A crater about 32 miles in diameter and about 9700 feet deep, devoid of a central cone. It appears on the upper part and near the middle of Plate XIII. The plateau has five minute craters upon it. On the east outside are two small craters, the lesser of which, about 2·75 miles diameter, has a central cone. We specially note this fact, because it is the smallest crater but one in which we have detected a central cone: no doubt, however, many smaller craters possess this unmistakable stamp of true volcanic origin, but so minute are the specks of light which the central cones of such very small craters reflect, that they fail to be visible to us.

East of Thebit is a very remarkable straight cliff 60 miles long by about 1000 feet high, called by some observers the “Railway,” and apparently the result either of an upheaval or of a down-sinking of the surface of the circular area across whose diameter it stretches.

Under moderate magnifying power, this cliff appears straight, but with higher power and under favourable conditions, its face is seen to be serrated, and along the upper edge may be detected several very minute craters. A more conspicuous small crater is seen at the north end of the cliff. To the east of the cliff nearly opposite the centre are two craters, from the east side of the larger of which proceeds a fine crack parallel to the cliff and passing through a dome-shaped hill of low eminence.

PLATO, 210 (41·8—81·8). Plate XIV.

This crater, besides being a conspicuous object on account of its great diameter, has many interesting details in and around it requiring a fine instrument and favourable circumstances to render them distinctly visible. The diameter of the crater is 70 miles; the surrounding wall or rampart varies in height from 4000 to upwards of 8000 feet, and is serrated with noble peaks which cast their black shadows across the plateau in a most picturesque manner, like the towers and spires of a great cathedral. Reference to our illustration will convey a very fair idea of this interesting appearance. On the north-east inside of the circular wall or rampart may be observed a fine example of landslip, or sliding down of a considerable mass of the interior side of the crater’s wall. The landslip nature of this remarkable detail is clearly established by the fact of the bottom edge of the downslipped mass projecting in towards the centre of the plateau to a considerable extent. Other smaller landslip features may be seen, but none on so grand and striking a scale as the one referred to. A number of exceedingly minute craters may be detected on the surface of the plateau. The plateau itself is remarkable for its low reflective power, which causes it to look like a dingy spot when Plato is viewed with a small magnifying power. The exterior of the crater wall is remarkable for the rugged character of its formation, and forms a great contrast in that respect to the comparatively smooth unbroken surface of the plateau, which by the way is devoid of a central cone. The surrounding features and objects indicated in our illustration are of the highest interest, and a few of them demand special description.

THE VALLEY OF THE ALPS (37·0—86·0). Plate XIV.

This remarkable object lays somewhat diagonally to the west of Plato; when seen with a low magnifying power (80 or 100), it appears as a rut or groove tapering towards each extremity. It measures upwards of 75 miles long by about six miles wide at the broadest part. When examined under favourable circumstances, with a magnifying power of from 200 to 300, it is seen to be a vast flat-bottomed valley bordered by gigantic mountains, some of which attain heights upwards of 10,000 feet; towards the south-east of this remarkable valley, and on both sides of it, are groups of isolated mountains, several of which are fully 8000 feet high. This flat-bottomed valley, which has retained the integrity of its form amid such disturbing forces as its immediate surroundings indicate, is one of the many structural enigmas with which the lunar surface abounds. To the north-west of the valley a vast number of isolated mounds or small mountains of exudation may be seen; so numerous are they as to defy all attempts to count them with anything like exactness; and among them, a power of 200 to 300 will enable an observer, under favourable circumstances, to detect vast numbers of small but perfectly-formed craters.

PICO, 211 (41·9—87·3). Plate XIV.

This is one of the most interesting examples of an isolated volcanic “mountain of exudation,” and it forms a very striking object when seen under favourable circumstances. Its height is upwards of 8000 feet, and it is about three times as long at the base as it is broad. The summit is cleft into three peaks, as may be ascertained by the three-peaked shadow it casts on the plain. Five or six minute craters of very perfect form may be detected close to the base of this magnificent mountain. There are several other isolated peaks or mountains of the same class within 30 or 40 miles of it which are well worthy of careful scrutiny, but Pico is the master of the situation, and offers a glorious subject for realizing a lunar day-dream in the mind’s eye, if we can only by an effort of imagination conceive its aspect under the fiercely brilliant sunshine by which it is illuminated, contrasted with the intensely black lunar heavens studded with stars shining with a steady brightness of which, by reason of _our_ atmosphere intervening, we can have no adequate conception save by the aid of a well-directed imagination.

TYCHO, 30 (43·0—142·3). Plate XVI.

This magnificent crater, which occupies the centre of the crowded group in our Plate, is 54 miles in diameter, and upwards of 16,000 feet deep, from the highest ridge of the rampart to the surface of the plateau, whence rises a grand central cone 5000 feet high. It is one of the most conspicuous of all the lunar craters, not so much on account of its dimensions as from its occupying the great focus of disruption from whence diverge those remarkable bright streaks, many of which may be traced over 1000 miles of the moon’s surface, disregarding in their course all interposing obstacles. There is every reason to conclude that Tycho is an instance of a vast disruptive action which rent the solid crust of the moon into radiating fissures, which were subsequently occupied by extruded molten matter, whose superior luminosity marks the course of the cracks in all directions from the crater as their common centre of divergence. So numerous are these bright streaks when examined by the aid of the telescope, and they give to this region of the moon’s surface such an extra degree of luminosity, that, when viewed as a whole, their locality can be distinctly seen at full moon by the unassisted eye as a bright patch of light on the southern portion of the disc. (See Plate III.) The causative origin of the streaks is discussed and illustrated in Chapter XI.

The interior of this fine crater presents striking examples of the concentric terrace-like formations that we have elsewhere assigned to vast landslip actions. Somewhat similar concentric terraces may be observed in other lunar craters; some of these, however, appear to be the results of some temporary modification of the ejective force, which has caused the formation of more or less perfect inner ramparts: what we conceive to be true landslip terraces are always distinguished from these by their more or less fragmentary character.

On reference to Plate III., showing the full moon, a very remarkable and special appearance will be observed in a dingy district or zone immediately surrounding the exterior of the rampart of Tycho, and of which we venture to hazard what appears to us a rational explanation: namely, that as Tycho may be considered to have acted as a sort of safety-valve to the rending and ejective force which caused, in the first instance, the cracking of this vast portion of the moon’s crust—the molten matter that appears to have been forced up through these cracks, on finding a comparatively free exit by the vent of Tycho, so relieved the district immediately around him as to have thereby reduced, in amount, the exit of the molten matter, and so left a zone comparatively free from the extruded lava which, according to our view of the subject, came up simultaneously through the innumerable fissures, and, spreading sideways along their courses, left everlasting records of the original positions of the radiating cracks in the form of the bright streaks which we now behold.

“WARGENTIN,” 26 (57·5—140·2). Plate XVII.

This object is quite unique of its kind—a crater about 53 miles across that to all appearance has been filled to the brim with lava that has been left to consolidate. There are evidences of the remains of a rampart, especially on the south-west portion of the rim. The general aspect of this extraordinary object has been not unaptly compared to a “thin cheese.” The terraced and rutted exterior of the rampart has all the usual characteristic details of the true crater. The surface of the high plateau is marked by a few ridges branching from a point nearly in its centre, together with some other slight elevations and depressions; these, however, can only be detected when the sun’s rays fall nearly parallel to the surface of the plateau.

To the north of this interesting object is the magnificent ring formation Schickard, whose vast diameter of 123 miles contrasts strikingly with that of the sixteen small craters within his rampart, and equally so with a multitude of small craters scattered around. There are many objects of interest on the portion of the lunar surface included within our illustration, but as they are all of the usual type, we shall not fatigue the attention of our readers by special descriptions of them.

ARISTARCHUS, 176 (6·3—99·2), and HERODOTUS, 175 (63·2—99·6). Plate XVIII.

These two fine examples of lunar volcanic craters are conspicuously situated in the north-east quarter of the moon’s disc. Aristarchus has a circular rampart nearly 28 miles diameter, the summit of which is about 7500 feet above the surface of the plateau, while its height above the general surface of the moon is 2600 feet. A central cone having several subordinate peaks completes the true volcanic character of this crater: its rampart banks, both outside and inside, have fine examples of the segmental crescent-shaped ridges or landslips, which form so constant and characteristic a feature in the structure of lunar craters. Several very notable cracks or chasms may be seen to the north of these two craters. They are contorted in a very unusual and remarkable manner, the result probably of the force which formed them having to encounter very varying resistance near the surface.

Some parts of these chasms gape to the width of two to three miles, and when closely scrutinized are seen to be here and there partly filled by masses which have fallen inward from their sides. Several smaller craters are scattered around, which, together with the great chasms and neighbouring ridges, give evidence of varied volcanic activity in this locality. We must not omit to draw attention to the parallelism or general similarity of “strike” in the ridges of extruded matter; this appearance has special interest in the eyes of geologists, and is well represented in our illustration.

Aristarchus is specially remarkable for the extraordinary capability which the material forming its interior and rampart banks has of reflecting light. Although there are many portions of the lunar surface which possess the same property, yet few so remarkably as in the case of Aristarchus, which shines with such brightness, as compared with its immediate surroundings, as to attract the attention of the most unpractized observer. Some have supposed this appearance to be due to active volcanic discharge still lingering on the lunar surface, an idea in which, for reasons to be duly adduced, we have no faith. Copernicus, in the remarkable bright streaks which radiate from it, and Tycho also, as well as several other spots, are apparently composed of material very nearly as highly reflective as that of Aristarchus. But the comparative isolation of Aristarchus, as well as the extraordinary light-reflecting property of its material, renders it especially noticeable, so much so as to make it quite a conspicuous object when illuminated only by earth-light, when but a slender crescent of the lunar disc is illuminated, or when, as during a lunar eclipse, the disc of the moon is within the shadow of the earth, and is lighted only by the rays refracted through the earth’s atmosphere.

There are no features about Herodotus of any such speciality as to call for remark, except it be the breach of the north side of its rampart by the southern extremity of a very remarkable contorted crack or chasm, which to all appearance owes its existence to some great disruptive action subsequent to the formation of the crater.

WALTER, 48 (37·8—131·9), and adjacent Intrusive Craters. Plate XX.

This Plate represents a southern portion of the moon’s surface measuring 170 by 230 miles. It includes upwards of 200 craters of all dimensions, from Walter, whose rampart measures nearly 70 miles across, down to those of such small apparent diameter as to require a well practized eye to detect them. In the interior of the great crater Walter a remarkable group of small craters may be observed surrounding his central cone, which in this instance is not so perfectly in the centre of the rampart as is usually the case. The number of small craters which we have observed within the rampart is 20, exclusive of those on the rampart itself. The entire group represented in the Plate suggests in a striking manner the wild scenery which must characterize many portions of the lunar surface; the more so if we keep in mind the vast proportions of the objects which they comprise, upon which point we may remark that the smallest crater represented in this Plate is considerably larger than that of Vesuvius.

ARCHIMEDES, 191 (40·3—95·8), AUTOLYCUS, 189 (36·8—95·5), ARISTILLUS, 190 (37·0—93·3), and the APENNINES. Plate IX.

This group of three magnificent craters, together with their remarkable surroundings, especially including the noble range of mountains termed the Apennines, forms on the whole one of the most striking and interesting portions of the lunar surface. If the reader is not acquainted with what the telescope can reveal as to the grandeur of the effect of sunrise on this very remarkable portion of the moon’s surface, he should carefully inspect and study our illustration of it; and if he will pay due regard to our previously repeated suggestion concerning the attached scale of miles, he will, should he have the good fortune to study the actual objects by the aid of a telescope, be well prepared to realize and duly appreciate the magnificence of the scene which will be presented to his sight.

Were we to attempt an adequate detail description of all the interesting features comprised within our illustration, it would, of itself, fill a goodly volume; as there is included within the space represented every variety of feature which so interestingly characterizes the lunar surface. All the more prominent details are types of their class; and are so favourably situated in respect to almost direct vision, as to render their nature, forms, and altitudes above and depths below the average surface of the moon most distinctly and impressively cognizable.

Archimedes is the largest crater in the group; it has a diameter of upwards of 52 miles, measuring from summit to summit of its vast circular rampart or crater wall, the average height of which, above the plateau, is about 4300 feet; but some parts of it rise considerably higher, and, in consequence, cast steeple-like shadows across the plateau when the sun’s rays are intercepted by them at a low angle. The plateau of this grand crater is devoid of the usual central cone. Two comparatively minute but beautifully-formed craters may be detected close to the north-east interior side of the surrounding wall of the great crater. Both outside and inside of the crater wall may be seen magnificent examples of the landslip subsidence of its overloaded banks; these landslips form vast concentric segments of the outer and inner circumference of the great circular rampart, and doubtless belong to its era of formation. Two very fine examples of cracks, or chasms, may be observed proceeding from the opposite external sides of the crater, and extending upwards of 100 miles in each direction; these cracks, or chasms, are fully a mile wide at their commencement next the crater, and narrow away to invisibility at their further extremity. Their course is considerably crooked, and in some parts they are partially filled by masses of the material of their sides, which have fallen inward and partially choked them. The depths of these enormous chasms must be very great, as they probably owe their existence to some mighty upheaving action, which there is every reason to suppose originated at a profound depth, since the general surface on each side of the crater does not appear to be disturbed as to altitude, which would have been the case had the upheaving action been at a moderate depth beneath. We would venture to ascribe a depth of not less than ten miles as the most moderate estimate of the profundity of these terrible chasms. If the reader would realize the scale of them, let him for a moment imagine himself a traveller on the surface of the moon coming upon one of them, and finding his onward progress arrested by the sudden appearance of its vast black yawning depths; for by reason of the angle of his vision being almost parallel to the surface, no appearance of so profound a chasm would break upon his sight until he came comparatively close to its fearful edge. Our imaginary lunar traveller would have to make a very long détour, ere he circumvented this terrible interruption to his progress. If the reader will only endeavour to realize in his mind’s eye the terrific grandeur of a chasm a mile wide and of such dark profundity as to be, to all appearance, fathomless—portions of its rugged sides fallen in wild confusion into the jaws of the tortuous abyss, and catching here and there a ray of the sun sufficient only to render the darkness of the chasm more impressive as to its profundity—he will, by so doing, learn to appreciate the romantic grandeur of this, one of the many features which the study of the lunar surface presents to the careful observer, and which exceed in sublimity the wildest efforts of poetic and romantic imagination. The contemplation of these views of the lunar world are, moreover, vastly enhanced by special circumstances which add greatly to the impressiveness of lunar scenery, such as the unchanging pitchy-black aspect of the heavens and the death-like silence which reigns unbroken there.

These digressions are, in some respects, a forestallment of what we have to say by-and-by, and so far they are out of place; but with the illustration to which the above remarks refer placed before the reader, they may, in some respects, enhance the interest of its examination.

The upper portion of our illustration is occupied by the magnificent range of volcanic mountains named after our Apennines, extending to a length of upwards of 450 miles. This mountain group rises gradually from a comparatively level surface towards the south-west, in the form of innumerable comparatively small mountains of exudation, which increase in number and altitude towards the north-east, where they culminate and suddenly terminate in a sublime range of peaks, whose altitude and rugged aspect must form one of the most terribly grand and romantic scenes which imagination can conceive. The north-east face of the range terminates abruptly in an almost vertical precipitous face, and over the plain beneath intense black steeple or spire-like shadows are cast, some of which at sunrise extend fully 90 miles, till they lose themselves in the general shading due to the curvature of the lunar surface. Nothing can exceed the sublimity of such a range of mountains, many of which rise to heights of 18,000 to 20,000 feet at one bound from the plane at their north-east base. The most favourable time to examine the details of this magnificent range is from about a day before first quarter to a day after, as it is then that the general structure of the range as well as the character of the contour of each member of the group can, from the circumstances of illumination then obtaining, be most distinctly inferred.

Several comparatively small perfectly-formed craters are seen interspersed among the mountains, giving evidence of the truly volcanic character of the surrounding region, which, as before said, comprises in a comparatively limited space the most perfect and striking examples of nearly every class of lunar volcanic phenomena.

We have endeavoured on Plate XXIII. to give some idea of a landscape view of a small portion of this mountain range.