volcanic ridges and chains by the entire absence of bold serrations upon their summits.

fro of the moon, and so, at such times, becomes more obvious. Professor Schmidt, the distinguished astronomer of Athens, who has given close study to this interesting spot since the year 1866, is of opinion that there certainly must have been substantial change in the form of the object since he began to watch it with narrow scrutiny. Mr. Nasmyth, on the other hand, doubts whether any absolute visible change has really occurred.

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. It has been estimated that towards the termination of its long scorching day of 300 hours the surface of the moon must have been heated to something more than twice the temperature of boiling water, probably about to the fusing-heat of tin, and that towards the end of its equally long 300 hours' night it must have been cooled pretty well to the temperature of interstellar space, which is 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 concentration 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 the two bodies as respects their volcanic age, tute a comparison between the condition of risen out of the mouth of the crater, and using the one as a basis for inference concernspread 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

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

the sight of objects of such transcendent antiquity as to render the oldest geological features of the earth modern by comparison. In regard to the possibility of the existence of any form of living organization at all comparable to the vital structures which teem so abundantly, and in such infinite diversity, upon the earth, there is no room for speculation or question. No vegetable organization could exist in the entire absence of moisture, and where at brief intervals of fourteen days the heat is of sufficient intensity to melt the least stubborn of metals, and then the cold immeasurably below that which is ever experienced in the arctic regions of the earth-where the usual monthly range of temperature is more than seven hundred degrees of Fahrenheit's thermometric scale, or nearly four times the difference between freezing ice and boiling water. Neither could any form of living animal, which the most lively physiological imagination could conceive, maintain the conditions of even the lowest kind of vitality in an atmosphere so rare that it could not sustain the column of the barometer the smallest fractional part of an inch.

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, and we may consider that the volcanoes now active over the surface of the globe represent the last expiring efforts of its eruptive force. Now in the earth we perceive several conditions wherefrom we may infer that it parted with its cosmical heat (and therefore with its prime source of volcanic agency) at a rate which will appear relatively very slow when we come to compare the like conditions in the moon. We may, we think, take for granted that the surface of a planetary body generally determines its heat-dispersing power, while its volume determines its heat-retaining power. Given two spherical bodies of similar material but unequal magnitude and originally possessing the same degree of heat, the smaller body will cool more rapidly than the larger, by reason of the greater proportion which the surface of the smaller sphere bears to its volume than that of the larger sphere to its volume this proportion depending upon the geometrical ratio which the surfaces of spheres bear to their volumes, the contents of spheres being as the cubes, and the surfaces as the squares, of their diameters. The volume of the earth is forty-nine times as great as that of the moon, but its surface is only thirteen times as great; there is consequently in the earth a power of retaining its cosmical heat nearly four times as great as in the case of the moon; in other words, the moon and earth being supposed at one time to have had an equally high tem- Mr. Nasmyth is not only an earnest perature, the moon would cool down to a expositor of the orthodox views of the old given low temperature in about one-fourth the Plutonian cosmogony, which teaches the time that the earth would require to cool to molten condition of the orbs of space as the same temperature. But the earth's cosmi- antecedent to their consolidation into cal heat has without doubt been considerably rocky, hard-coated spheres, he is also a conserved by its vaporous atmosphere, and still more by the ocean in its antecedent va- thorough believer in the yet broader and porous form. Yet, notwithstanding all this, more comprehensive assumptions of the the earth's surface has nearly assumed its final elder Herschel and of Laplace, which condition, so far as volcanic agencies are con- trace back the formation of liquid spheres cerned; it has so far cooled as to be subject to the condensation of nebulous vapour. to no considerable distortions, or disruptions, Mr. Nasmyth holds that no more satisof its surface. What, then, must be the state factory, or more philosophical, explanaof the moon, which, from its small volume and tion of the origin of cosmical heat can be large proportionate area, parted with its heat given than the one which attributes it to at the above comparatively rapid rate? The the influx, and consequent impact, of matter of the moon is, too, less dense than that of the earth, and hence, doubtless, from material particles, drawn simultaneously this cause disposed to more rapid cooling; together by gravitating force, and to the and it has no atmosphere or vaporous en- conversion of the arrested motion of the velope to retard its radiating heat. We are concentrating mass into the rotary movedriven thus to the conclusion that the moon's ment of the constituent molecules; and loss of cosmical heat must have been so rapid he refers, in terms of strong admiration, as to have allowed its surface to assume its to the labours, in this department of refinal conformation ages on ages ago, and search, of Julius Robert Mayer, of Heilhence that it is unreasonable and hopeless to bronn, and of Dr. Joule, of Manchester, look for evidence of change of any volcanic character still going on.... Speaking by our as establishing the now generally ac own lights, from our own experience and cepted principle of the conservation and reasoning, we are disposed to conclude that indestructibility of the physical forces of in all visible aspects the lunar surface is un- nature, and of the convertibility of mochangeable, that in fact it arrived at its tion into heat. He quotes, in illustration

of this part of his argument, the estimate | members of the planetary system are of Professor Helmholtz, as to the amount spheres in which small solid nuclei are of heat that would be generated by the enveloped in deep liquid oceans, or atcondensation of the entire mass of the mospheres, that have lost, in the further solar system-sun, planets, and worlds process of cooling, all shining power, -from the nebulous into the liquid although they still scatter radiant heat state; and which assumes a quantity that into space, and so perform the subordiwould be enough to raise a mass of water nate function of "heat-suns." In the of the same weight 28,000,000° C. There views of Mr. Nasmyth our own pleasant is, of course, a wide range for speculation world is but a more finished production in this part of the subject, but it will not in which the still molten, and yet radiant, be forgotten how much more coherence central nucleus has been shut up in a and meaning such speculative considera- thick, cold shell of consolidated subtions have acquired since the spectro-stance; and the moon is the ultimate and scope has been brought to bear in inves- final issue of the same process, in which tigating the physical conditions of the the cold, solid crust has extended to the luminaries of space. In connection with very core, and all has become a chilled these pages of Mr. Nasmyth's book, re- cindery mass, in which the outer pittings ferring to the earliest periods of the his- and frettings are the only vestiges that tory of the moon, there will come to the remain to tell of the fiery ordeal which mind of the reader the discoveries re- has been passed through. cently made concerning the existing state Mr. Proctor, in his recently printed of the great solar orb, which tell of col- description of "The Moon," has, in that umns of luminous gas thousands of miles portion of the work which is especially high, and streams of white-hot meteoric devoted to " aspect, scenery, and physihailstones millions of miles long, shot cal condition," travelled essentially over out from volcanic vents in the sun's in- the same ground as Mr. Nasmyth, and in candescent, and certainly fluid, surface; doing so he has strongly marked the disof clouds of dark, heavy fumes, seem-tinction that there is between making a ingly of condensing metallic vapours, rolled back into the whirling rents; of the engraven hieroglyphics-the dark lines of Fraunhofer-traced upon the prismatic spectrum of the sunbeam, to record that the rays sent forth from the [and views of inquirers who have worked incandescent sphere have to penetrate in this field. In this gathering there apthrough a dense investment of heavy pear the pittings of the moon's surface sublimations and vapours before they can with meteoric rain, the groovings and emerge into transparent space. The scorings of its rocks with glacial action, most recent conclusions of this powerful the manufacture of annular craters by the method of research, it will be remem- bursting of surface bubbles, the fracturbered, point to those brightest luminaries ing of the hardened crust, and the fusion of the celestial hierarchy-the white of subjacent rock by the impact of the as isolated spheres in which concussion; and the swallowing up of heavy fumes of magnesium, sodium, and primeval seas by the opening out of iniron are kept scintillating in oceans of ternal cavities and caverns. Perhaps glowing gas, very much after the manner upon the whole, the part of these maniin which molecules of unsublimed carbon fold references which takes the strongest are kept scintillating in jets of glowing hold upon the reader's attention is Mr. hydrogen in the flames of artificial illu- Proctor's comments upon the views of mination; and to the lower grade of Mallet, first fully developed in an article yellow stars and red stars as kindred contributed to the "Philosophical Magaspheres more surface-chilled, in which zine" of December 1872, which ascribe, yet thicker vapours and agglomerating the development of volcanic energy, and scoriæ are gathering around the inner the fusion of rock, to the crushing-in of bright nucleus and dulling its lustre very large broken masses of the crust of the much as the white-hot brightness of earth, and to the production of lakes and molten iron, in the founder's hands, is pockets of red-hot lava of comparatively dimmed through the various tints of yel-limited extent, where the mechanical imlow and red while the fiery heat subsides. pulse of the shattering and dislocation is Yet other steps in the same line of argu- transformed intc heat. Over and above ment suggest that the larger and outer his favourable regard for this theory, Mr.

stars

book in years and writing a book in days. Mr. Proctor has brought together, and he has done this with a considerable manifestation of ability and industry, a copious collection of references to the labours

Proctor seems to incline, in dealing with When, some two centuries ago, Sir the moon's formative history, to the no- Isaac Newton was engaged in knotting tion that "processes of contraction and the first meshes of the marvellous net of of gathering-in of matter from without," intellectual apprehension that has since have sufficed "to produce all the effects enveloped a firmament of worlds and of disturbance which have brought the suns, it was fortunately a correlative fact moon to its present condition." As an that there was one bright luminary, movexponent of this particular part of the ing so swiftly and punctually round in the theme, namely, the description of the heavens, among the stars, and so ostenphysical state and history of the moon, tatiously and demonstratively marking its Mr. Nasmyth's book is very much like course over those illuminated graduations the Wargentin of his illustrations a of the nocturnal sky, that it at once sugcup full to the rounded brim with out-gested itself as a ready and obvious test welling substance furnished from within, of the accuracy of the great mathematiwhile Mr. Proctor's book has the aspect cian's novel conception. Newton was rather of an agglomeration of matter indeed, for a passing instant, so staggered "pitted with meteoric rain," and fash-by the very aptness and sufficiency of this ioned from the gathering-in of extraneous rough-and-ready proof that he was, for contributions. This remark, however, is the time, thrown off the scent of his wonto be understood as limited to that por-derful discovery. In common with other tion of the subject which of necessity mathematicians of the day he had adopted comes most immediately into comparison an erroneous estimate of the size of the with the work of Mr. Nasmyth. Mr. earth, and valued each degree of the meProctor is very much more original and ridian as having a span of sixty miles. very much more at home when he deals When he attempted to square the movewith the more congenial theme of "thements of the moon, and the necessities of motions" of the moon, which will presently be spoken of.

vestigation, the French astronomer, Picard, detected the error in the earth's measure, and extended the length of a degree of the meridian to sixty-nine miles and an eighth. When this correction was taken into account in the calculations of Newton it immediately appeared that his assumption of the identity of the force that made a stone fall to the ground, and that made the moon curve, in its remote orbit, towards the earth, was substantially correct, and from that time the Newtonian theory of gravitation became an assured possession of human science, to be thenceforth wielded by astronomers and mathematicians to interminable and momentous issues.

his theory, with this old estimate, as the Imedium of the comparison, it was maniAttempts were made, even as early as fest that the movements and the theory the middle of the seventeenth century, to could not be made to agree. But by one construct maps of the moon, in which all of the lucky coincidences that sometimes the objects that had been discovered by occur in mundane affairs, it happened the telescope were sketched in their rela-that, just at the critical moment of the intive positions. In 1837 the Germans Beer and Maedler published a really splendid map of the moon, thirty-seven inches across, in which all the leading objects, amounting to several hundreds in number, are laid down, the names of the older observers being for the most part attached to them. Mr. Proctor has included in his book a very good copy of Beer and Maedler's map on a reduced scale. Mr. Nasmyth, on his part, has given in his volume what he aptly terms a "Picture map of the Moon; a chart which is constructed upon an altogether novel and very admirable plan. In it the objects are all represented in the bold relief of light and shadow which they acquire under the most favourable circumstances of illumination. The several objects are, therefore, shown as they never can be seen altogether at one time; but each one has the aspect and individuality by which it is best known, when viewed in its most pronounced form in the telescope, fringed by the shadows of oblique light. On account of the readiness with which each familiar object is caught by the eye; this is a very excellent and welcome expedient.

The proof which the moon furnished of the truth of Newton's conception of the universality of gravitation was simply and essentially this. The moon circles about the earth at a distance of sixty of the earth's half-diameters from the terrestrial surface, and therefore in a position where, if the assumption of the theory that gravitating force diminishes in proportion to the distance from which it is exerted be correct, the attraction of the earth should be sixty times less than

it is at the earth's surface. The moon cause of the disturbance can be tracked should therefore be drawn, by the earth's to its hidden lair. The searching-out of attraction, as far in one minute (which is these minor perturbations of the moon sixty seconds) as a stone at the earth's has been carried on, since Newton's surface is drawn in one second. Now time, with unceasing attention, and, inthe moon at its distance of sixty half-deed, is still persevered in with everdiameters of the earth, or 240,000 miles, increasing rigour and exactness. The moves through a circular path which is 1,646,015 miles long; and it performs this journey in 27 days, 7 hours, 43 minutes, or in 39,343 minutes; and in order that it may complete such a journey in such a time it has to move round in a curve which falls out, towards the earth, from a straight course, 16 7-9 feet every 419 miles. Now 419 miles is the distance through which the moon moves in a minute; and therefore the moon does fall towards the earth, under its attraction, 16 7-9 feet in a minute; just as a stone falls towards the surface of the earth 16 7-9 feet in a second. Consequently the force which draws the moon and the force which draws the stone is one and the same, its power being only diminished sixty times in the case of the moon, because it is exerted from a distance sixty times as great.

perfecting, as it is called, of the tables of the moon is the staple work of all the most important national observatories, amongst which, in this point of view, the Royal Observatory at Greenwich stands certainly pre-eminent. This progressive correction of the tables of the moon is entirely a process of continued comparison of exact instrumental observation of the satellite's place amongst the stars with calculations that have been made beforehand, so that any failure of the moon to take some special place that has been assigned to it for that particular instant, may furnish the clue to fresh causes of disturbance and perturbation, which may be used for insuring better forecasts in the future when they have been tracked and ascertained.

The Royal Observatory at Greenwich was built in the reign of Charles II. " for In reality, however, the moon does not the rectifying the tables of the motions move in an exactly circular path, and of the heavens, and the places of the with unchanging velocity. It is some- fixed stars, so as to find out the longitimes a little nearer to, and sometimes a tudes of places for the perfecting the art little farther from, the earth; and it of navigation." Flamsteed, a contemposweeps along with a pace that is some-rary of Newton, was appointed the first times a little more rapid, and sometimes "astronomical observer" of the king, or a little less rapid, than 419 miles in the "astronomer royal,” in 1674, and the minute; and these irregularities are due, work of the observatory was commenced not to any one influence, but to the com-in 1676. The earliest mural circle, or bination of a very large number of sep- large circle attached to the face of a. arate influences that vary in direction and wall, with a graduated scale, for exact force from instant to instant, and that observations in the meridian, was concan nevertheless be hunted down by the structed by Flamsteed at his own exrelentless scent of mathematical analysis, pense in 1689, and with this exact inand that must be hunted down, and fixed, strument the systematic study of the each in its exact integrity, if the moon's moon's movements was initiated, two movements are to be calculated before- years after the publication of the "Prinband, and tabulated in such a form that cipia," which contained the final develthey can be turned to account by sailors opment of Newton's great theory. In in navigating their ships upon the wide, 1694 Flamsteed supplied Newton with a trackless sea. This regulated irregular- series of observed places of the moon ity, indeed, is the great charm which the for use in his calculations. A notable moon's movements have for practical as- illustration is afforded of the appreciatronomers; for it has been found through tion which was given to astronomical scia long experience that each fresh dis-ence at this time in the fact that the first covery of an irregularity of movement mural circle in the observatory was coninfallibly leads also to the discovery of a structed at Flamsteed's own expense; previously missing link in the chain of that Flamsteed's salary for his public the Newtonian theory. Each particular service was 100l. per annum, with a deirregularity is due to some special inter-duction of 10l. per annum for a tax, and ference that invariably hangs upon the action of gravity somewhere. There fore having seized the irregularity, the

was coupled with the condition that he should instruct two of the Christchurch schoolboys in nautical astronomy; and