but such landslip-formations are readily ity as a restraining check and, in addidistinguished in every case from the true tion to this, the more brittle, and intrinsiring-shaped barriers of primary eruption, cally less dense, substance of the lunar by their being short, broken segments of crust that has been moulded and sculp ridges, instead of continuous rings. The tured by the volcanic energy appear to outer circular ridges of the larger craters be the chief modifying conditions that are commonly seen to be strengthened establish a distinction between the priby external buttresses, which are streams mary volcanic, or Plutonic, disturbances of consolidated lava that have been of the earth and the final and ultimate poured from distinctly visible secondary volcanic disturbances of the moon. craters upon their sides. The hollowed- In the not unfrequent instances of out cavities of the most boldly pro-walled-in, crater-like depressions of the nounced craters seem to have been moon's surface, in which volcanic modelcaused by the eroding action of the ling is less obviously marked, first on erupted lava; and such craters as are account of the absence of all trace of devoid of the characteristic central cones peaks of eruption on the inner floors, and of residual force are held to have had often on account also of the less promimolten lava quietly welled up towards the nent character of the surrounding piledtermination of the eruption from the up rims, Mr. Nasmyth nevertheless holds primary central vents until the lakes of that the same instrumentality may be acliquid rock have risen within the limiting cepted. He thinks that even in the bulwark higher and higher, and have broad smooth-floored craters, with low finally covered and masked all vestiges and slight walls, such as Grimaldi, and of the inner eruptive peaks. Wargentin perhaps Shickard immediately below is shown in one of the drawings as the Wargentin, the external limiting bulnotable instance of a bulwarked crater warks have been formed by the outflow which has been left, in this way, brimful. of molten lava from inner vents, in conMr. Nasmyth adopts it as an aphorism nection with which concentric waves of that the size of the crater is simply the liquefied substance have been propavisible expression of the strength of the gated outwards, as on the surface of a eruption which has been concerned in pool, until circular banks of consolidatits formation, and that the larger craters ing and cooling scoriæ have been pressed are essentially the first-fruits of the up at the outer margin, and left there as young-born eruptive power, and therefore permanent ramparts. When these ramolder formations in point of time than the parts have once been made, subsequent smaller craters; and he conceives that flooding of liquid lava would easily whenever a violent eruption stopped sud- efface all vestige of the central source of denly, it left as the memorial monument the eruption; but the surface of the subof the effort a large ring-shaped and high-sequently consolidated pool would still walled crater, and that whenever a gentle commonly show the mouths of the small eruption died gradually away, it either outlets through which the last streams of piled up its monumental record higher the supply had been poured, as is the and higher into a pyramid or sharp-point-case with Shickard and all pits of a simed cone, or spread its smooth pavement of lava. He holds that the best-developed forms of the lunar craters in reality represent volcanic force in its purest state and its highest perfection, and that the moon is thus virtually a model of the radical operations of volcanic processes, devoid of the disturbing and masking effects brought about by such secondary agencies as water and air, and presenting to the contemplation of telescopic observers very much what the solid foundations of the earth would show if it were cleared of its water-worn groovings and furrowings, its water-formed sedimentary beds, and its oceans and rivers. The larger extent and freedom of the primary eruptions, due to the more rapid cooling of the smaller sphere, and to the inferior power of grav ilar character. In many the flat floors of the inner plateaux are literally freckled with small secondary craters. The grandest specimen of the smooth-floored craters is, perhaps, the magnificent object which is known as Plato, and which is the subject of one of Mr. Nasmyth's most remarkable drawings. In this crater, which has a clear diameter of seventy miles, the limiting bulwark towers up to a varying height of from 4.000 to 8,000 feet, and jagged peaks at the top cast long serrated shadows half way across the inner plain, where innumerable craters spangle the floor. In this splendid specimen, however, there has obviously been piling-up influence at work in the construction of the outer wall. In one part there is a very remarkable and character istic instance of the segmentary terrace attributable to a landslip. appear to have been produced by the gentle oozing of molten lava from narrow In many of the finest craters the cen- orifices, and the piling-up of heaps of its tre of the floor is occupied by a perfect consolidating substance around; in the cluster of peaks, instead of by a solitary case of the loftiest and boldest protruone. Aristotle, Eudoxus, Theophilus, sions the vent remaining open, and the Tycho, and super-eminently Copernicus, discharging orifice rising with the growth are instances of this peculiarity. Mr. of the mountain until great altitude has Nasmyth has been at considerable pains been attained. Telescopic powers, magto show that in these cases the multipli- nifying 300 diameters, show that the ridges cation of the central eruptive cone has and flanks of these clustered peaks are in been due to the sudden arrest and subse- reality studded with minute but perfectly quent diversion of the primary outburst. formed volcanic craters. The small size A casual choking of the original vent has of these vents plainly indicates that they thrown the rising stream out in a new belong to a comparatively gentle phase direction, where the obstruction and re- of volcanic action, in which the exuding sistance were less; and in this way, by forces were destitute of the higher explorepeated arrests and fresh diversions of sive energies. Mountain chains in the the eruptive force, cone has successively moon have resulted, not from the shattergrown upon cone, until a cluster of peaks ing, uptilting, folding, and puckering of has been reared before the subsiding hard rocky beds, but from the comparaeffort has finally been exhausted. The tively slow and long-sustained escape of small secondary craters studding smooth lava through multitudinous openings and level floors of consolidated lava have burst in weak parts of the surface-crust. probably a similar formative history. This view of the matter is remarkably Mr. Nasmyth thinks that the whole of confirmed by these ranges of the moon these secondary mouths are diverticula being found in the least-disturbed porof older central channels of eruption, and tions of the lunar surface, and not where that each of them has been opened out the volcanic power has had most eneras the eruptive force was opposed by getic play. There are no continuous gathering impediments in the older course clusters and ranges about Tycho and of the outflow. Walter, where crater is crowded upon Large clusters and continuous ranges crater in endless and almost inextricable of mountain elevation are by no means confusion, as is shown in a notable decommon upon the moon, but they do oc- lineation contained in the twentieth plate cur. The finest examples of them are of Mr. Nasmyth's book, where more than seen in the two groups of prominences 200 large craters had to be sketched. They which have been called the Apennines lie almost exclusively, on the other hand, and the Alps. The Apennines are a in the quite northern region where the grand range rising from a comparatively so-called Sea of Serenity and Sea of smooth and unbroken plain, and extend- Showers extend their smooth, almost ing to a distance of 450 miles. Some of ocean-like, surfaces over hundreds of the peaks on this mighty chain rise with square miles. They in reality form the almost precipitous faces to a height of circumscribing boundaries of the plain18.000 and 20,000 feet, and cast black districts that can be seen in the moon, sharp-pointed shadows sometimes to the even by the unaided eye, as broad dark extent of ninety miles from their bases. patches. The sharp, serrated, and spireThe Alps consist of a broad cluster of like shadows cast by the boldest peaks, peaks, a little to the west of Plato, mount- however, by no means of necessity indiing from 8,000 to 10,000 feet high, and cut cate that the extruded masses through in one part by a remarkable flat- similar needle-like forms; for Mr. Nasbottomed valley, six miles wide and sev-myth demonstrates, by the actual photoenty-five miles long. The terminal sum-graph of a long shadow thrown by a pea, mits in this group are in some parts so that even a round eminence has a long, densely clustered as to render it an im- pointed, index-like shadow when the practicable task to count them. Mr. Nas- light falls upon it at a very oblique angle myth, however, believes that all peaked of incidence. Many of the sharply shadand clustered mountains on the moon of owed eminences in the moon may really this character are still essentially volcanic | be as dome-shaped and rounded as ordiexudations, and not veritable mountain nary volcanic protrusions upon the earth. ridges in the terrestrial acceptation. In Pico, the finest isolated peak upon the the moon even these mountain systems moon, which rises from the level surface, are of just to the south of Plato, to a towering full moon. These extend over the plain height of 8,000 feet, and which casts a around Copernicus to the distance of long-pointed shadow more than thirty one hundred miles, and are of closer miles upon the surrounding plain, is and finer form, and of a more reticulated sketched by Mr. Nasmyth as a rugged, character, than the rays of Tycho. The ridged, and buttressed pyramid as broad crater which stands on the focal centre again at its base as it is high. of this system of radiant fissures is fortysix miles across, and has a limiting bulwark 12,000 feet high, divided into concentric terraced ridges which are in many parts obviously enormous landslips that have been crushed down by the overloaded summits, and that have scattered their débris in vast segmental heaps below. Gaps can, in many places, be traced in the higher ramparts from which these landslips have fallen. On the central plateau of the crater there is a fine cluster of eruptive cones, in three instances rising to a height of 2,400 feet above the floor. Mr. Nasmyth developes with considerable force and clearness the connection that there seems to be between fissures and continuous lines of craters upon the moon. He considers that when a long fissure had been opened out in the thickening and consolidating crust, a mountain chain was formed if the exuding was gentle and continuous; but that successive craters, ranged in a linear progress, one after the other, were opened out if the exuding force was sudden, intermittent, and violent. That the eruptive force which has been brought into operation in shattering Besides these systems of bright radithe solidified shell of the moon has been ant streaks, there are innumerable other very deep-seated, and very large, is un-indications of shatterings and fissures mistakably evident. Towards the south-which seem to have taken place at a later ern part of the moon's face there is a period of the moon's formative history, pole of eruption which has starred the when the outer shell had not yet finally hard shell around it very much as the settled down into its condition of permacracks are starred over the shell of the nent repose, but when the epoch of the glass globe in Mr. Nasmyth's experi- formation of volcanic vents and of the ment. This pole of eruption is the well-outpouring of molten rock had entirely known crater of Tycho, which is appar- passed away. The cracks of this later ent to the unaided eye as a centre of bril-age have remained open and gaping, so liancy in the full moon. The radiating that at periods of oblique illumination streaks which have been traced issuing they are seen as black, shadow-filled out around this crater are more than one lines. They extend to varying distances hundred in number, and some of them up to 150 miles, are from one to two can be followed for at least 600 miles in miles wide in the broadest part of their length, that is for about a tenth part of span, taper away to their extremities, and the moon's circumference. They are are of unfathomable depths. They occur only visible in the full moon because the in very many parts of the lunar surface, original fissures, which have been opened but very fine examples of them are seen out in the hard brittle shell, have been around Triesnecker, Mercator, Arissince filled up with a bright shining tarchus, Copernicus, and along the base material that has subsequently welled up of the Apennines. Drawings of these from within, and that can be seen under have been made, and appear in the pardirect light glistening like polished sil- ticular sketches of these objects. There ver, although it is lost to view when the are also, it may be remarked, continuous brilliant glare is thrown off sideways in ridges of less bold relief and of lower oblique illumination. This subsequent elevation scattered about on the moon, infiltration appears to have scarcely risen which Mr. Nasmyth believes to be true above the outer surface of the sphere, as specimens of wrinkling, rather than of no shadows are cast from its edges in volcanic eruption, essentially caused by oblique light, although it has spread out the shrinking and shrivelling of the outer to a certain extent over the edges of the shell as it sank down to its temperature crack, and has been bevelled down to the of final repose. The ridges of this charlevel beneath. There are streaks of this acter are most abundantly seen over the class that are estimated to measure in plain surface of the Ocean of Storms bewidth more than twenty-five miles! Co-tween Copernicus and Gassendi, and pernicus is the centre of a similar system of bright rays that come into sight in the directly incident sunshine of the about the otherwise smooth spaces of the Sea of Tranquillity. They are, for the most part, distinguished from the true volcanic ridges and chains by the entire absence of bold serrations upon their summits. strong probability, ascribed to the difference of illumination at different times. At one time oblique light fills the hollow Mr. Nasmyth has been led by his long of the crater with black shade, and comcourse of patient observation and reflect- municates to it a tenfold distinctness, ive study to the conviction that the moon and then at another time direct sunshine had arrived, even long ages preceding so illumes the spot that the crater itself, the periods of the earth's pre-human his- robbed of its shadows, is only discernible tory, at the stage of unbroken and un- to very excellent telescopes, while a changeable rest. The only forces which broad patch of highly luminous and appear to be now at work in the great brightly reflecting substance (like that lunar wilderness effecting movement and of the radiant streaks of Tycho and of change are the monthly vicissitudes of Copernicus), which surrounds the crater, temperature, and the consequent expan- comes into prominent and conspicuous sion and contraction to which the surface-visibility. This change of illumination solids are subjected as they pass alter-is sometimes more intensely and effectnately from the fourteen terrestrial days ively produced than it is at other correof unintermitting and never-clouded sun-sponding periods of the lunation, on shine to the fourteen days of equally un-account of the libratory swaying to and interrupted deprivation of the sun's rays. fro of the moon, and so, at such times, beIt has been estimated that towards the comes more obvious. Professor Schmidt, termination of its long scorching day of the distinguished astronomer of Athens, 300 hours the surface of the moon must who has given close study to this interhave been heated to something more esting spot since the year 1866, is of than twice the temperature of boiling opinion that there certainly must have water, probably about to the fusing-heat been substantial change in the form of of tin, and that towards the end of its the object since he began to watch it equally long 300 hours' night it must with narrow scrutiny. Mr. Nasmyth, on have been cooled pretty well to the tem- the other hand, doubts whether any abperature of interstellar space, which is solute visible change has really occurred. 250 degrees lower than the zero of Fahren- Mr. Nasmyth, however, is led to his heit's heat-scale. Recurrent changes of view of the unchangeable fixedness of the this violent character in all probability moon's present state by a process of reamay still exert some mechanical influ- soning that is altogether independent of ence among the brittle rocky projections mere observation and watching of the of the ridged craters and peaked moun- lunar face by the telescope, and that is so tains, and even at times produce a re- pre-eminently characteristic of the entire newal of the terrace-forming landslips. method and spirit of the work which has In two particulars only have any sus-enabled him to make this notable contripicions arisen of the presentation of act-bution to the scientific study of the earth's ive phenomena in the moon since it has satellite, that it is obviously well his conbeen watched under the advantage that clusion should be told in his own graphic powerful telescopes confer. A bright and forcible language. He says: flame was at one time believed to be visible in the middle of the crater of Aristarchus when the moon's face was dark. This appearance has now been pretty well demonstrated to be due to the con The theoretical view of the question, which we have now to consider, has led us, however, former volcanic activity lingers in the moon to the strong belief that no vestige of its - that it assumed its final condition an incon centration of secondary earth-shine into ceivable number of ages ago, and that the a kind of bright focus by the concave high interest which would attach to the close mirror-like arrangement of the polished scrutiny of our satellite, if it were still the hollow of this crater. Also in more re-theatre of volcanic reactions, cannot be hoped cent times a small crater known as Linné, for. If it be just and allowable to assume which is placed upon the level surface of that the earth and the moon were condensed the Sea of Serenity, not far from the ex- into planetary form at nearly the same epoch tremity of the Apennines, disappeared, (and the only rational scheme of cosmogony and a large white spot presented itself justifies the assumption), then we may instiin its place, as if a broad white cloud had tute a comparison between the condition of risen out of the mouth of the crater, and using the one as a basis for inference concernthe two bodies as respects their volcanic age, spread over it in the form of an impene- ing the state of the other. We have reason trable canopy or screen. This too, how-to believe that the earth's crust has nearly ever, is now, with all the appearance of assumed its final state so far as volcanic reac : tions of its interior upon its exterior are terminal condition cons of ages ago, and that concerned we may affirm that within the in the survey of its wonderful features, even historical period no igneous convulsions of in the smallest details, we are presented with any considerable magnitude have occurred, the sight of objects of such transcendent anand we may consider that the volcanoes now tiquity as to render the oldest geological active over the surface of the globe represent features of the earth modern by comparison. the last expiring efforts of its eruptive force. Now in the earth we perceive several condi- istence of any form of living organization In regard to the possibility of the extions wherefrom we may infer that it parted with its cosmical heat (and therefore with its at all comparable to the vital structures prime source of volcanic agency) at a rate which teem so abundantly, and in such which will appear relatively very slow when infinite diversity, upon the earth, there is we come to compare the like conditions in the no room for speculation or question. moon. We may, we think, take for granted No vegetable organization could exist in that the surface of a planetary body generally the entire absence of moisture, and where determines its heat-dispersing power, while its at brief intervals of fourteen days the volume determines its heat-retaining power, heat is of sufficient intensity to melt the Given two spherical bodies of similar material least stubborn of metals, and then the but unequal magnitude and originally possess cold immeasurably below that which is ing the same degree of heat, the smaller body will cool more rapidly than the larger, by reaever experienced in the arctic regions of son of the greater proportion which the surface the earth where the usual monthly of the smaller sphere bears to its volume than range of temperature is more than seven that of the larger sphere to its volume -this hundred degrees of Fahrenheit's therproportion depending upon the geometrical mometric scale, or nearly four times the ratio which the surfaces of spheres bear to difference between freezing ice and boiltheir volumes, the contents of spheres being ing water. Neither could any form of as the cubes, and the surfaces as the squares, of living animal, which the most lively phystheir diameters. The volume of the earth is iological imagination could conceive, forty-nine times as great as that of the moon, maintain the conditions of even the lowbut its surface is only thirteen times as great; there is consequently in the earth a power of est kind of vitality in an atmosphere so retaining its cosmical heat nearly four times rare that it could not sustain the column as great as in the case of the moon; in other of the barometer the smallest fractional words, the moon and earth being supposed at part of an inch. one time to have had an equally high temperature, the moon would cool down to a given low temperature in about one-fourth the time that the earth would require to cool to the same temperature. But the earth's cosmical heat has without doubt been considerably conserved by its vaporous atmosphere, and still more by the ocean in its antecedent vaporous form. Yet, notwithstanding all this, the earth's surface has nearly assumed its final condition, so far as volcanic agencies are concerned; it has so far cooled as to be subject to no considerable distortions, or disruptions, of its surface. What, then, must be the state of the moon, which, from its small volume and large proportionate area, parted with its heat at the above comparatively rapid rate? The matter of the moon is, too, less dense than that of the earth, and hence, doubtless, from this cause disposed to more rapid cooling; and it has no atmosphere or vaporous envelope to retard its radiating heat. We are driven thus to the conclusion that the moon's loss of cosmical heat must have been so rapid as to have allowed its surface to assume its final conformation ages on ages ago, and hence that it is unreasonable and hopeless to look for evidence of change of any volcanic character still going on. . . . Speaking by our own lights, from our own experience and reasoning, we are disposed to conclude that in all visible aspects the lunar surface is unchangeable, that in fact it arrived at its Mr. Nasmyth is not only an earnest expositor of the orthodox views of the old Plutonian cosmogony, which teaches the molten condition of the orbs of space as antecedent to their consolidation into rocky, hard-coated spheres, he is also a thorough believer in the yet broader and more comprehensive assumptions of the elder Herschel and of Laplace, which trace back the formation of liquid spheres to the condensation of nebulous vapour. Mr. Nasmyth holds that no more satisfactory, or more philosophical, explanation of the origin of cosmical heat can be given than the one which attributes it to the influx, and consequent impact, of material particles, drawn simultaneously together by gravitating force, and to the conversion of the arrested motion of the concentrating mass into the rotary movement of the constituent molecules; and he refers, in terms of strong admiration, to the labours, in this department of research, of Julius Robert Mayer, of Heilbronn, and of Dr. Joule, of Manchester, as establishing the now generally accepted principle of the conservation and indestructibility of the physical forces of nature, and of the convertibility of motion into heat. He quotes, in illustration |