,,modern ,,cosmogonies ,by the ,same ,author ,a ,,popular ,,history ,,of ,,astronomy ,,during ,,the ,,nineteenth ,,century ,,fourth ,,edition4 ,,demy #h,,vo41 ,,cloth1 ,,illustrated ,,price #aes4 ,,net ,,problems ,,in ,,astrophysics ,,demy #h,,vo41 ,,cloth1 ,,illustrated ,,price #bjs4 ,,net ,,the ,,system ,,of ,,the ,,stars ,,second ,,edition ,,demy #h,,vo41 ,,cloth1 ,,illustrated ,,price #bjs4 ,,net ,a4 ,c4 ,black ,soho ,square ,london1 ,w4 ',the world's a prophecy of worlds to come4'--,young ,,modern ,,cosmogonies ,,by ,,agnes ,m4 ,,clerke ,,hon4 ,,mem4 ,r4,a4,s4 ,,author ,,of ',a ,,popular ,,history ,,of ,,astronomy ,,during ,,the ,,nineteenth ,,century1' ',,the ,,system ,,of ,,the ,,stars1' ',,problems ,,in ,,astrophysics1' ,,and ,,other ,,works ,,london ,,adam ,,and ,,charles ,,black #aije ,,preface ,of the sixteen chapters constituting this little work1 thirteen have been published as a series1 begun in ,knowledge and continued in ,knowledge and ,illustrated ,scientific ,news1 and to the proprietors of those journals1 for their courteous permission to reprint them1 ,i offer my sincere thanks4 ,three additional chapters1 equivalent to1 though not identical with1 those that now appear1 formed an integral part of the original plan of the book1 now presented to the public in the hope that it will enable general readers to follow1 with the profound interest it should inspire1 the course of modern inquiries regarding the origin of the world4 ,their advance is by no means smooth or facile4 ,many difficulties and perplexities are encountered in the attempt to get back towards the beginning of things4 ,some of the old tracks1 too1 have been torn up by the pioneers of twentieth century science1 and the process of constructing new ones1 which shall lead further into the unknown fore-time1 is slow and laborious4 ,but the rail-head in the desert is a peculiarly suggestive place of pilgrimage1 and several such outlying posts and temporary halting-places are more or less vaguely localized in the following pages4 ,london1 ,november1 #af1 #aije4 ,,contents ,,chapter ,,page ,i4 ,,from ,,thales ,,to ,,kant #a ,,ii4 ,,the ,,nebular ,,hypothesis #ba ,,iii4 ,,criticisms ,,of ,,the ,,nebular ,,hypothesis #ci ,,iv4 ,,the ,,nebular ,,hypothesis ,,varied ,,and ,,improved #fj ,v4 ,,tidal ,,friction ,,as ,,an ,,agent ,,in ,,cosmogony #hc ,,vi4 ,,the ,,fission ,,of ,,rotating ,,globes #ajj ,,vii4 ,,world-,,building ,,out ,,of ,,meteorites #aah ,,viii4 ,,cosmogony ,,in ,,the ,,twentieth ,,century #ace ,,ix4 ,,protyle3 ,,what ,,is ,,it8 #aej ,x4 ,,universal ,,forces #aff ,,xi4 ,,the ,,inevitable ,,ether #ahc ,,xii4 ,,the ,,forms ,,of ,,nebul #aii ,,xiii4 ,,the ,,procession ,,of ,,suns #baf ,,xiv4 ,,our ,,own ,,system #bcb ,,xv4 ,,remnants ,,and ,,survivals #bej ,,xvi4 ,,life ,,as ,,the ,,outcome #bfe ,,index #bhc ,,modern ,,cosmogonies ,,chapter ,i ,,from ,,thales ,,to ,,kant ,very few even of the most savage tribes are content to take the world just as it is without speculating as to how it came to be4 ,for time has three dimensions--past1 present1 and future--and we can no more restrict our thoughts within one of them than we can exist corporeally in ,flatland4 ,we are1 indeed1 told that the ,abipones and ,esquimaux refuse to trouble themselves with questions of origin1 on the ground that the hard facts of life leave no room for otiose discussions2 but even they feel obliged to justify their incuriosity4 ,in easier circumstances they1 too1 would claim the entirely human privilege of 'looking before and after1' as their forgotten progenitors may have done4 ,it is1 indeed1 difficult to think at all about the framework of nature without attempting to divine1 were it only by a crude surmise1 the process of its construction4 ,we are instinctively convinced that there is no such thing as fixity of condition4 ,so far1 ,heracleitus was in the right4 ,experience tells us of continual change in ourselves and whatever surrounds us4 ,reason teaches us that its minute momentary effects1 if pursued backward for an indefinite time1 must sum up to a prodigious total4 ,no limit1 that is to say1 can be put to the difference between what is and what was4 ,yet the machinery of modification must somehow have been set going4 ,an initial state is prescribed by logical necessity4 ,and the start was made on certain terms--it was 'conditioned4' ,but the conditioned implies the absolute2 ordinances1 an enactive power4 ,the inevitableness of the connection has been more or less obscurely perceived wherever men have tried to establish some kind of accord between phenomena and intuition1 with results legible in the wavering outlines of many primitive cosmogonies4 ,only1 however1 in the ,hebrew ,scriptures has the idea of ,creation been realized in all its fulness and freedom2 elsewhere the gods invoked to bring the world into existence themselves demanded a birth-history1 a theogony being the usual and necessary prelude to a cosmogony4 ,nevertheless 'picture-thoughts' 7it has been well said71#a and nothing more1 were represented by these prefatory genealogies4 ,night and darkness loomed into personal shape1 and from the obscurity of their union the creatures of light radiantly sprang1 and proceeded1 according to a predetermined law of order1 to sort out the elements of chaos and dispose them into cosmical harmony4 ,this mythical phase of thought terminated in ,greece with the rise of the ,ionian ,school of ,philosophy4 ,immemorial legends1 discredited by the advent of a new wisdom1 took out a fresh lease of life under the guise of folk-lore2 ,orphic fables were left to the poets and the people2 and the sage of ,miletus set on foot a speculative tradition1 maintained by a long succession of metaphysicians down to the very threshold of the recent scientific epoch4 ,all were what we should call evolutionists--,thales of ,miletus no less than ,descartes and ,swedenborg2 their main object1 in other words1 was to find a practicable mode of evoking a systematic arrangement of related parts from the monotony of undifferentiated confusion4 ,now1 in essaying this enterprise they encountered two distinct problems4 ,one was concerned with the nature of the primeval world-stuff2 the other with the operations to which it had been submitted4 ,modern theorists have made it their primary object to expound the mechanism of cosmic growth--the play of forces involved in it1 the transformations and progressive redistribution of energy attending it4 ,but questions of this kind could only in the scantiest measure be formulated by early thinkers1 who accordingly devoted their chief attention to selecting an appropriate material for the exercise of their constructive ingenuity4 ,thales asserted all things to have been derived from water1 and water is still among unsophisticated tribes the favourite ',urstoff4' ,anaximenes substituted air4 ,heracleitus gave the preference to the mobile and vital element 7as he thought it7 of fire4 ,anaximander1 on the other hand1 might put forward a colourable claim to priority over ,sir ,william ,crookes in the invention of 'protyle4' ,he imagined as the matrix of the world a boundless expanse of generalized matter1 containing potentially all the chemical species1 which1 separating out by degrees through the affinity of like for like1 formed1 by their contrasts and conjunctions1 the infinitely varied sum of things4 ,the successors of ,anaximander had recourse to spontaneously arising condensations and rarefactions as the mainspring of development2 but all these vague principles were quickly crowded into oblivion by the definite and intelligible doctrine of the 'four elements' enunciated by ,empedocles1 which1 guaranteed by the imprimatur of ,plato1 took a place unchallenged for nearly two millenniums among the fundamentals of science4 ,erroneous and misleading though it was1 it yet served as a means of regulating appearances and guiding vagrant ideas--it was a track to follow in the absence of any better method of orientation4 ,leucippus and his more famous disciples1 ,democritus and ,epicurus1 were the first who ventured to trace the mechanical history of the cosmos4 ,their primordial atoms were endowed with weight1 and it was weight or gravity which ultimately determined their spacial arrangement and mutual relations4 ,rectilinear in the first draft of the scheme1 their movements were somewhat arbitrarily deflected by ,epicurus2 and the gyrations thence ensuing eventually became1 so to speak1 authentic and precise in the ,cartesian vortices and in ,swedenborg's solar maelstrom4 ,kant's ,natural ,history of the universe was another1 though an entirely separate branch of the atomistic stock4 ,the ,democritean atoms1 however1 and in a lesser degree the ,kantian atoms1 differed essentially from the ultimates of chemical analysis postulated by ,dalton4 ,they were a scratch lot--an incongruous assortment of fragments1 rather than of elementary portions of matter1 indefinitely various in size1 shape1 and mass4 ,nor was this diversity created as a mere play of fancy4 ,it was strictly necessary to the plan of action adopted4 ,for1 apart from heterogeneity1 there could obviously be no development4 ,absolute uniformity involves absolute permanence4 ,change can originate only through inequality4 ,there must be a tilt of level before the current will begin to flow2 some cause of predominance is needed to set it going in a given direction4 ,here1 of a surety1 is the initial crux of all cosmogonists4 ,they usually surmount it by assuming the occurrence of casual condensations1 secure against disproof1 while incapable of verification4 ,the expedient thus begs the question4 ,theories of world-history made an integral part of antique philosophy4 ,each founder of a school aimed at establishing a complete system of knowledge1 co-extensive with phenomena1 embracing all things1 from the primum mobile overhead to the blade of grass underfoot1 and rationalizing the past1 present1 and future of the comprehensive whole4 ,modern science is less ambitious4 ,aspiring to no such vast synthesis1 it is content to make laborious acquaintance with the facts of nature1 to ponder their implications1 and1 if possible1 to reconstruct on the basis supplied by them the condition of things in the 'dim backward' of unmeasured time4 ,by no such means1 it is true1 can their beginning in any real sense be arrived at2 the weapons of induction become blunted long before they strike home to the heart of that mystery2 yet the recognition of their inadequacy brings compensation in a fuller mastery over their properly adapted use4 ,science1 so called1 was1 indeed1 down to the ,baconian era1 a turbid mixture of physics with metaphysics4 ,the solution1 it might be said1 was attempted of an insoluble material which refused to dissolve and was hindered from precipitating4 ,the ,greek view of nature was essentially pantheistic4 ,the ,ionian speculators appear to have presumed without expressly insisting upon its self-regulating power4 ,aristotle alone emphatically rejected the doctrine of cosmic vitality or sub-conscious tendencies4 ,but ,plato accepted and magnified the ,oriental tradition2 the conception of a ',world-,soul' owed to him its vague splendour and perennial fascination4 ,the function of the ,platonic vice-creator 7for such the ,world-,soul must be accounted7 was that of moulding brute matter into conformity with the archetypal ideas of the ,divine mind2 this was not1 however1 accomplished once for all1 but by a progressive spiritualizing of what in its nature was dead and inanimate4 ,the spiritual agent1 becoming incorporated with the universal frame1 lent to it a semblance of life1 an obscure sensitiveness1 and even some kind of latent intelligence2 and so the anima mundi was shaped into existence1 and continued century by century to be the subject and source of imaginings beyond measure wild and fantastic4 ,one great thought--that of the unity of nature--lay behind them1 but its significance was lost amid the phantasmagoria of ,neo-,platonist exaltations4 ,hence the ,bacchic fervours of ,giordano ,bruno took their inspiration2 here was the groundwork of ,spinoza's pantheism4 ,shelley's ,demiorgon1 felt as 'a living spirit1' seen as 'a mighty darkness1' descended lineally from that strange essence--formless1 inarticulate1 devoid of individual self-consciousness--which animated the submerged philosophy of ,neo-,pagan times with the barren ardours of mysticism4 ,the doctrine1 in its original and more sober version1 obtained memorable expression in ,virgil's melodious hexameters3 ',principio clum1 ac terras1 camposque liquentes1 ,lucentemque globum lun1 ,titaniaque astra1 ,spiritus intus alit1 totamque infusa per artus ,mens agitat molem1 et magno se corpore miscet4' ,in ,conington's rhymed version they run as follows3 ',know first1 the heaven1 the earth1 the main1 ,the moon's pale orb1 the starry train1 ,are nourished by a soul1 ,a bright intelligence1 whose flame ,glows in each member of the frame1 ,and stirs the mighty whole4' ,kepler was no cosmogonist1 but he aspired to found a 'physical astronomy1' and in his gropings for a mechanical power that might suffice to regulate the movements of the heavenly bodies1 he stumbled upon a mode of action highly appropriate for the explanation of their growth4 ,his ignorance of the laws of motion precluded him from the conception of velocities persistent in themselves1 and merely deflected from straight into curved paths by a constant central pull4 ,hence he was driven to the twofold expedient of creating a whirling medium for maintaining the revolutions of the planets1 and of supposing the sun to exercise a 'magnetic influence1' by which they were drawn into closed orbits4 ,here1 then1 central forces made a definitive entry on the astronomical stage1 although with scarcely a discernible promise of their brilliant future4 ,but it was otherwise with the clumsy machinery they helped to animate4 ,kepler's simple modus operandi1 adopted1 or more probably re-invented by ,descartes1 was published as an epoch-making discovery in his ,principia ,philosophica 7#afdd71 and sprang under its new aspect into swift notoriety4 ,the wide acceptance of the theory of vortices was at least in part due to the impressive largeness of its framework4 ,descartes left nothing out4 ,the spacious scope of his speculations embraced all that was knowable--nature1 animate and inanimate1 life and time3 ',planets and the pale populace of heaven1 ,the mind of man1 and all that's made to soar4' ,a philosophy1 a metaphysic1 and a cosmogony were linked together in a single plan4 ,its author distinguished in matter three gradations of fineness4 ,the coarsest kind was that composing the earth and other opaque bodies2 the more sublimated materials of the sun and stars came next2 finally1 there was the ethereal substance of the skies1 so delicately constituted as to be luminous or luminiferous4 ,this last variety was regarded as of subordinate origin4 ,it represented1 in fact1 a kind of celestial detritus4 ,interstellar space had gradually become filled with intangible dust1 the product of molecular attrition among originally angular solar and stellar particles4 ,ether was thus supposed to bear to the subtlest description of ordinary matter very much the same sort of relationship that ions presumably do to atoms4 ,enough has been said to show that the ,cartesian universe was based on crude atomism4 ,its mode of construction1 moreover1 evinced a total disregard of mechanical principles4 ,yet some acquaintance with the laws of motion was by that time easily within reach4 ,the first of the three1 at any rate1 had been unmistakably enounced by ,galileo in #afcb1 and ,descartes himself strongly championed its validity4 ,yet he thought it necessary1 in order to keep the planets moving1 to immerse them in one great self-gyrating vortex centred on the sun1 each being further provided with a similar subordinate whirlpool for the maintenance of its domestic system4 ,comets were left in a singularly anomalous position4 ,they circulated freely on the whole1 their exemption from planetary restrictions being tacitly recognized2 nevertheless1 they took advantage of every encountered swirl to help themselves on towards their destination4 ,among the fables of pseudo-science ,delambre declared that1 had the choice been offered to him1 he would have preferred the solid spheres of ,aristotle to the tourbillons of ,descartes4 ',the spheres1' he added1#b 'have proved helpful both for the construction of planetariums representing in a general way the celestial movements1 and for their calculation by approximate rules deduced from them2 but the system of vortices has never served any purpose whatsoever1 whether mechanical or computative4' ,its vogue had1 nevertheless1 been brilliant and sustained4 ,advanced thinkers in the time of ,louis ,quatorze piqued themselves upon being ,cartesians4 ,the vortical hypothesis was novel--it seemed daring2 and though it might not be true1 it had plausibility enough for fashionable currency4 ,nor did it deserve the unmitigated contempt with which it was treated by ,delambre4 ,a glance at the skies makes us pause before condemning it to scornful oblivion4 ,just two centuries after its promulgation the first spiral nebula was identified in ,canes ,venatici4 ,that the heavens swarm with analogous objects is certain1 and their status as partially developed systems is visible in every line of their conformation4 ,our own planetary world may1 or may not1 have traversed the stage they so copiously illustrate2 but in any case they prove beyond question that vortices variously conditioned are prevalent among the forms assumed by cosmic masses advancing towards an orderly arrangement4 ,mystical cosmogonies belong to the period of ethnic infancy4 ,they have not ceased to be current4 ,world-fables must be invented wherever the obscure wonder of savage communities is excited by the mysterious spectacle of ,nature's apparently designed operations and irresistible power4 ,but they were superseded among peoples in the van of progress by philosophic cosmogonies at the epoch when ,thales began to diffuse throughout ,ionia the wisdom of the ,egyptians and ,chaldeans4 ,schemes1 however1 such as he and his successors elaborated result from the discourse of reason unfettered by any close attention to facts4 ,they have been mostly wrought out by men who1 in ,delambre's words1 ',dissertaient perte de vue1 sans jamais rien observer1 et sans jamais rien calculer4' ,the insubstantial fabrics reared by them were then fatally discredited by ,baconian methods and the ,newtonian reign of law2 they survived--forms of thought die slowly--but insecurely1 with noticeably undermined foundations4 ,swedenborg was the last eminent reactionary1 and his restoration in #agcd of the ,cartesian gyrating medium as the motive power of the solar machine was a palpable failure4 ,it could not be otherwise1 since its inceptive idea had grown superannuated4 ,the modern era of scientific cosmogony was at hand4 ,it was preceded by some remarkable attempts at sidereal generalization4 ,cosmology is the elder sister of cosmogony4 ,what is must be studied before what was can be inferred4 ,precedent states remain visionary unless they can be closely linked to actual and observable conditions4 ,now about the middle of the eighteenth century an intelligible plan of the stellar universe1 so far as the telescope had then disclosed it1 began to be a desideratum4 ,and the enterprise of supplying the need was undertaken independently by two men of obscure origin and imperfect education--one ,english1 the other ,german4 ,thomas ,wright1 of ,durham1 was the son of a carpenter at ,byer's ,green1 where he was born ,september #bb1 #agaa4 ,his life was one of many vicissitudes1 but ended happily4 ,having struggled hard for a livelihood--now at sea1 then again on shore as a clock and almanac maker1 a teacher and lecturer--he finally attained1 somewhat unaccountably1 to distinction and affluence1 built himself a handsome house hard by his native shanty1 and prosperously and reputably inhabited it during a quarter of a century4 ,he died ,february #be1 #aghf1 just one year after ,herschel had described to the ,royal ,society the outcome of his first experiments in 'star gauging4' ,as the originator of the 'cloven disc' theory of the ,milky ,way1 ,wright is still deservedly remembered1 for although that majestic structure is assuredly otherwise designed1 it was no mean achievement to have initiated the science of its architecture4 ,heinrich ,lambert was a still more adventurous speculator than his unknown ,english rival4 ,his father was a poor tailor at ,mhlhausen1 then in ,swiss territory1 and he worked as his apprentice4 ,but his irrepressible talents brought him into notice1 and he died1 in #aggg1 through the favour of the second ,frederick1 a ,berlin ,academician4 ,his ,cosmological ,letters1 published in #agfa1 were entirely original2 they were composed in ignorance of what ,wright and ,kant had already written4 ,in some respects he overtopped them both4 ,he had splendid intuitions1 and just touched the confines of greatness4 ,and if his performances fell short of the very highest1 it may have been rather through abridgment of opportunity than through lack of capacity4 ,the ,milky ,way marked1 to his apprehension1 a sidereal ecliptic1 and he coincided with ,wright in regarding it as a disc of aggregated stars1 but with breaches and gaps indicating a multiplicity of systems circulating1 he thought1 round a common centre4 ,nor did he doubt the existence of other ,milky ,ways--numberless1 remote1 unseen--grouped into a combination of a higher order2 while beyond1 and still beyond1 stretched further hierarchies of systems on an ascending scale of magnitude and grandeur4 ,our knowledge of the structural facts of the universe can never be made exhaustive2 in the middle of the eighteenth century1 before ,herschel had opened his sidereal campaign1 it was barely elementary4 ,wright and ,lambert were accordingly on a stint of material--they had to make bricks with very little straw4 ,yet they did their best with what was at hand4 ,both paid profound attention to the stellar heavens2 they earnestly sought the true interpretation of the appearances presented by them1 holding it possible1 as we1 despite accumulating difficulties1 still do1 to harmonize countless detached phenomena in one vast synthetic plan4 ,it was this purpose of fidelity to ,nature which gave value to their work1 and made it a new thing in cosmological history4 ,this alone lent it impulsive force1 and caused the meditations of two lonely thinkers to become effective in stimulating fresh attempts1 favoured by improved conditions1 to comprehend what actually exists1 and to infer thence1 with rational confidence1 its sources in the vague but undeniable past4 ,,footnotes3 ,footnote #a3 ,zeller1 ,history of ,greek ,philosophy1 translated by ,s4,f4 ,alleyne1 vol4 i41 p4 #hf4 ,footnote #b3 ,quoted by ,r4 ,wolf1 ,handbuch der ,astronomie1 ,bd4 ,,ii41 p4 #eic4 ,,chapter ,,ii ,,the ,,nebular ,,hypothesis ,immanuel ,kant was1 in #agea1 still in the plastic stage4 ,his period of 'pure reason' was remote1 and might have appeared improbable4 ,such as they were1 his distinctions had been won in the field of concrete science1 and the world of phenomena invited his speculations more seductively than the subtleties of logic4 ,a seed was accordingly thrown into fertile soil by his reading of ,thomas ,wright's ,new ,theory of the ,universe1 as summarized in a ,hamburg journal4 ,it set him thinking1 and his thoughts proved to be of the dynamic order4 ,wright regarded the heavens under a merely statical aspect4 ,he laid down the first definite plan of their construction1 showing that the stars were not scattered at random1 but aggregated by method2 and this was much for one necessitous human being to have accomplished unaided4 ,but the young professor of ,knigsberg could not rest satisfied with the idle contemplation of any subsisting arrangement4 ,his mind was incapable of acquiescing in things simply as they presented themselves2 it craved to know further how they came to stand to each other in just such mutual relations4 ,he was1 moreover1 permeated with ,epicurean doctrines4 ,not in any reprehensible sense4 ,he could not be reproached either as a hedonist or as an atheist4 ,his pleasures were intellectual1 his morals austere1 his convictions orthodox4 ,behind the veil of material existence he divined its supreme immaterial ,originator1 and his perception of the activity in ,nature of an ordering ,first ,cause remained equally vivid1 whether its disclosures were taken to be by immediate creation or through tedious processes of modification and growth4 ,his large and luminous view embraced besides the ethical significance which such processes adumbrate4 ,the following sentence shows an appreciation of the place of man in ,nature truer and more profound than was attained perhaps by any other of his philosophical contemporaries3 ',the cosmic evolution of ,nature1' he wrote in memorable words1 'is continued in the historic development of humanity1 and completed in the moral perfection of the individual4'#c ,nevertheless1 he owned to a community of ideas with ,democritus as to the origin of the universe4 ,lucretius had cast over him the spell of his lofty diction1 and captured his scientific adhesion by the stately imagery of his verse4 ,with reservations1 however4 ,docile discipleship was not in his line4 ,he availed1 then1 of the ,democritean atoms1 but by no means admitted their concourse to be fortuitous4 ,chaos itself1 as he conceived it1 half concealed1 half revealed the rough draft of a 'perfect plan4' ,his postulates were few4 ,he demanded only a limitless waste of primordial matter1 animated by no forces save those of gravitation and molecular repulsion1 and undertook to produce from it a workable solar system4 ,the attempt was no more than partially successful4 ,retrogressive investigations lead at the best to precarious results1 and this one1 in particular1 was vitiated by a fundamental error of principle4 ,its author clearly perceived that planetary circulation must be the outcome of a vortical swirl in the nebulous matrix2 but he failed to see that no interaction of its constituent particles could have set this swirl going4 ,systems cannot of themselves add to their 'moment of momentum4' ,no changes of internal configuration avail to increase or diminish the sum of the products obtained by multiplying the mass of each of the connected bodies into its areal velocity projected on a common plane4 ,the sum is of the algebraic kind4 ,equal and opposite motions cancel each other1 the total representing only the aggregate excess of speed in either direction4 ,a system with all its parts in rapid motion might then conceivably be devoid of moment of momentum4 ,and if this were its state to begin with1 it should be its state to the end of time1 unless external force were applied to alter it4 ,but the possibility may be dismissed as ideal4 ,the establishment of so nice a balance as it would require is not practically feasible4 ,in the actual world one side of the velocity account would be sure to exceed the other1 albeit very slightly1 and the smallest predominance would suffice to set on foot an eventual rotation of the system4 ,had ,kant been better acquainted with mechanical principles1 he might then have safely trusted to the minute beginnings supplied by aboriginal inequalities of movement and dissymmetry of arrangement for the development in his colossal dust-cloud of the wheeling movement necessary for his purpose2 and he would thus have escaped stumbling at the threshold of his daring inquiry4 ,rightly averse to employing arbitrary expedients1 he piqued himself on the simplicity of his postulates1 and was thus misled into substituting an imaginary for a real cause4 ,the hypothesis adopted by him was that the particles forming the initial inchoate mass fell together by gravity1 but were deviated from rectilinear courses through the effects of unequal resistance4 ,and he derived from the combination of these multitudinous encounters a common axial rotation for the entire agglomeration4 ,the futility of this mode of procedure was adverted to by ,m4 ,faye in #ahhe4d ,the deviations in question would1 in fact1 exactly balance one another1 there being no reason why movement in one sense should prevail over movement in the opposite2 consequently a general rotatory movement could not even begin to affect the seething mass1 which would condense in sterile rigidity4 ,kant should then1 as ,laplace did when his turn came1 have assumed the gyration indispensable to his purpose4 ,he asked too little from ,nature on one side1 and too much on the other1 with the result of arresting the machinery he designed to set going4 ,kant made the germ of the future sun to consist in an aggregation of atoms at the core of the nebula1 which1 growing by successive innumerable accessions1 provided the motive power for the machinery of planetary construction4 ,for it was1 as we have seen1 the jostling of the particles drawn towards the gradually preponderating centre of attraction which set on foot1 it was supposed1 the whirl eventually transformed into the tangential velocities of the sun's attendant bodies4 ,they were formed1 like the sun1 by the perpetuation and increase of subordinate nuclei sure to arise in the elemental tumult4 ,they were formed1 not under the guidance of a definite law1 but just where chance--or what seemed like chance--favoured an accretion4 ,the progressive increase of planetary distances noted by ,titius and ,bode could never have arisen in the ,kantian system4 ,nor could the ,kantian planets have had a direct rotation4#e ,under the given conditions retrograde systems should have originated4 ,this would have necessarily ensued from the incoherence of their materials4 ,particles revolving independently one of the other have smaller velocities the more remote they are from the focus of movement4 ,should they agglomerate into a globe1 the inner flights must1 as being the swiftest1 determine the direction of its rotation1 which will consequently reverse the direction of its orbital revolution4 ,hence1 it depends upon the nature of their generating stuff no less than upon the advance of central condensation whether planets1 in their domestic arrangements1 contravene or obey the larger law of circulation prevailing in the system to which they belong1 and ,kant's nebula was undoubtedly such as to involve its contravention4 ,yet his scheme1 with all its deficiencies1 bore the authentic stamp of genius--of genius imperfectly equipped with knowledge1 but original1 penetrative1 divinatory4 ,the very entitling of the work1 ,a ,natural ,history of the ,heavens was an audacity implying a radical change of conception4 ,it was in this remarkable treatise that 'island universes' made their definitive appearance4 ,wright1 it is true1 had1 five years previously 7in #agej71 thrown out the idea that 'cloudy spots' might represent 'external creations1' but as a mere vagary of the scientific imagination4 ,kant unhesitatingly laid hold of it1 classed nebul as so many separate galaxies1 and regarded them as combining with our own into a revolving system on a surpassing scale of grandeur4 ,kant was also the first to take into account the effects on their development of the plasticity of the heavenly bodies4 ,he published in #aged1 in a ,knigsberg paper1 by way of preliminary to his forthcoming ,natural ,history1 an outline of the workings of tidal friction in the earth-moon system4 ,he saw clearly that it had acted in the past to reduce our satellite's rotation to its present minimum rate1 and that it even now1 by very slow degrees1 tended to retard the spinning of the earth4 ,this brilliant forecast remained unnoticed for well-nigh a century4 ,the assertion1 however1 that ,kant's cosmogony was an anticipatory ',meteoritic ,hypothesis' lacks foundation4 ,it is only true in the sense that his building materials were pulverulent1 not 'fluid4' ,laplace's primitive nebula was a coherent mass4 ,it rotated as a whole2 it divided only under considerable strain2 its separated parts had individual unity--they held together with1 so to speak1 a purpose of concentration4 ,kant's elemental matter1 on the contrary1 was a loose aggregate of independent particles1 each pursuing its way1 disturbed1 indeed1 by its neighbours1 but essentially isolated from them4 ,they were1 in short1 genuine ,lucretian atoms1 intended to stand for the irreducible minima of ,nature4 ,the chaos that they formed was in nowise a 'meteoritic plenum1' unless the phrase be emptied of all distinctive meaning4 ,meteorites1 so far from being primordial units1 have the show and semblance of advanced cosmical products4 ,they raise special questions in chemistry1 mineralogy1 geology1 and physics1 claiming to be dealt with by experts in each branch4 ,before serving for explanatory purposes1 in fact1 they themselves need to be explained4 ,laplace enounced his hypothesis in #agif1 and republished it with supplementary details in #ahjh4 ,herschel had meanwhile ascertained the retrograde movement of the ,uranian satellite-system1 a circumstance highly damaging to the validity of the adopted line of reasoning2 yet its author was content to leave it in jeopardy4 ,he must1 to be sure1 have regretted that ,nature had seen fit to mar the admirable symmetry indicative of her presumed plan of action1 running counter thereby to the plainest teachings of the doctrine of probabilities4 ,but he kept his own counsel on the subject1 preferring that it should be discussed1 as it has been in full detail1 by posterity2 and posterity has1 at any rate1 learned that the seeming caprices of ,nature are often more instructive than her most harmonious regularity1 and has derived a warning from her frequent breaches of continuity against the undue extension of apparently well-grounded inferences4 ,nevertheless1 the constructive scheme handed on by the eighteenth to the nineteenth century has not1 up to the present1 been consigned to the limbo of vanities4 ,it accorded too profoundly with undoubted realities to be thus summarily disposed of4 ,no one then living had studied the mechanism of the solar system so attentively1 or was so intimately acquainted with its workings1 as ,pierre ,simon ,laplace4 ,none knew better how admirable1 yet how far from inevitable1 were the adjustments by which its stability was secured4 ,long meditation upon their poise and plan persuaded him that the subsisting congruities of arrangement must have had their source in a community of origin4 ,he thus acquired the settled conviction that the sun engendered his cortge1 or was together with it engendered from one parent-mass4 ,and this virtually new truth 7for ,kant's speculation had attracted a negligible amount of notice7 was set forth by him with a directness and lucidity which won for it an immediate place among the permanent acquisitions of the human intellect4 ,few1 perhaps1 any longer believe that planetary formation took the precise course laid down for it in the ,systme du ,monde1 but fewer still doubt that the entire ambit of the solar system was once occupied by an inchoate sun1 and that its component bodies came into being incidentally to that sun's progressive contraction4 ,in favour of this view ,laplace could allege no clinching argument2 it recommended itself to him solely through its inherent probability4 ,unexpected confirmation has1 none the less1 been afforded to it by the modern theorem of the conservation of energy1 applied by ,helmholtz with widely illuminative effect to solve the problem of the maintenance of solar heat4 ,laplace assumed an enormously high initial temperature4 ,it was the only way open to him1 and he took it4 ,but a transcendentally hot nebula is not easily conceivable2 an exalted thermal state seems1 and probably is1 incompatible with a high degree of attenuation4 ,the key to the enigma was given by the demonstration that a diffuse mass1 although actually cold1 might contain vast stores of potential heat4 ,there was then no need to postulate a primitive 'fire-mist'2 the surrendered energy of position amply sufficed to meet the requirements of the case4 ,the temperature of the nebula necessarily rose as it contracted through gravitational stress2 shrinkage and heat-evolution proceeded together2 and they in all likelihood proceed together still4 ,our existence depends in part1 or wholly1 upon the collapse of the sun4 ,if its particles ceased to descend1 their incandescence would become less intense1 and terrestrial vitality would be seriously compromised4 ,their number1 however1 being finite1 the store of energy they can supply in falling even from an infinite distance is also finite4 ,the process of solar sustentation is then terminable2 it had a beginning1 and it will assuredly come to an end4 ,now the terminus ad quem is of a calculable remoteness3 it can be located 7unless shifted by radio-active processes7 within certain limits of time4 ,but the terminus a quo depends upon too many conditions to be satisfactorily defined4 ,it is only certain that the sun is to-day slightly more condensed than it was a year ago4 ,it might a few millenniums back have been measurably larger1 had modern micrometrical methods been available in the ,stone ,age2 while1 looking into the geological past1 we discern a continually more diffuse globe1 filling the orbit of ,mercury when the earth was perhaps still red-hot1 then successively ampler spheres1 out to1 and beyond1 that of ,neptune4 ,and just such a vastly diffused sun realizes the nebula of ,laplace4 ,the state of things he imagined can be reached accordingly1 either by tracing forward the development of a tenuous rotating mass1 or by pursuing backward the surely indicated1 unceasing1 and inevitable distension of the sun4 ,hence1 no sooner was it acknowledged that energy may be transformed1 but cannot be destroyed1 than the nebular cosmogony assumed a new and authoritative aspect4 ,but here a caveat has been entered by the latest inquirers--a caveat not to be ignored1 though based upon modes of action still exceedingly obscure4 ,radio-activity is a fledgling science2 its capabilities1 though immense1 are vaguely outlined4 ,until they more fully approve themselves1 it would be unwise to admit conclusions which they may eventually enforce4 ,subversive ideas are in the air2 the theory of atomic dissociation goes to the very root of things1 and it insistently claims assent4 ,its verification1 by disclosing the presence in the universe of a measureless store of unsuspected energy1 would overthrow all the calculations of cosmic time heretofore attempted1 and might protract indefinitely the radiative span of the sun4 ,mr4 ,w4 ,e4 ,wilson pointed out in #aijcf that its entire thermal output could be supplied by the spontaneous liberation of energy from #cf grammes of radium in each cubic metre of its volume2 and although we have no evidence of the actual existence of radium in the sun1 the possibility that chromospheric helium represents the decay of solar radio-active elements#g must be taken into consideration4 ,the ground here is undermined with pitfalls4 ,we can only see that although ,helmholtz's gravitational rationale of the sun's long life-history remains true1 the results derived from it may be profoundly modified by co-ordinate processes1 variously efficacious according to circumstances1 perhaps knowable1 but as yet unknown4 ,the scope of the nebular hypothesis had widened prodigiously by the time ,helmholtz took it in hand4 ,five years before its promulgation at ,paris1 ,herschel gave at ,slough the first hint of a corresponding scheme of sidereal evolution4 ,the discovery of a nebulous star in ,taurus 7,n4,g4,c4 #aead7 set him pondering2 and he found himself1 as the upshot of his meditations1 reduced to the dilemma either of concluding nucleus and chevelure to be alike stellar1 though composed of stars differing enormously in real magnitude1 or of admitting the possession by the star of a voluminous appendage constituted of a peculiar and unknown 'shining fluid4' ,he chose the latter alternative1 adding the pregnant remark3 ',the shining fluid might exist independently of stars1' and 'seems more fit to produce a star by its condensation than to depend on the star for its existence4'#h ,thus tentatively1 and under the compulsion of phenomena rather than by the deliberate choice of its inventor1 the universal theory of the genesis of stars from nebul took its rise4 ,herschel shaped it definitively in #ahaa and #ahad into a formal plan for the interpretation of celestial appearances1 but in a large and general way4 ,he made no attempt to realize the particularities of a modus operandi vaguely conceived of as involving growth by absorption or assimilation4 ,he and ,laplace thought out their separate schemes quite irrespectively one of the other4 ,there is no evidence of their having exchanged views personally or by correspondence1 nor does their mutual influence appear to have been appreciable4#i ,yet ,laplace needed as the raw material for his solar system precisely the 'shining fluid' elaborated1 one might say1 by ,herschel1 partly through the revelations of his telescopes1 partly as the outcome of his reasonings concerning the chevelure of the star in ,taurus4 ,halley1 it is true1 had1 by a sagacious intuition1 surmised the composition of nebul out of a 'lucid medium4' ,but the ineffectual phrase remained stranded in the pages of the ,philosophical ,transactions1 and has only of late been set floating on the stream of scientific literature4 ,down to the end of the eighteenth century world-building had been a purely speculative undertaking4 ,it lacked actuality2 it was concerned with operations thought of as belonging exclusively to a past order of things1 now over and done with1 and lying wholly outside the range of experience4 ,through ,herschel's synthesis1 however1 those dimly apprehended operations were brought into view as variously progressing even now in different parts of the cosmos1 as incipient in some regions1 far advanced in others1 the rubbish of the workshop here half masking the rising edifice1 while elsewhere signs of decay and exhaustion give legible presage of an appointed end4 ,and this stupendous vision of a forming universe has not vanished on critical scrutiny4 ,it is no dream-tissue2 it cannot dissolve into airy nothingness2 it is based upon a firm substratum of reality4 ,the immeasurable purposes of creative wisdom are still only in part fulfilled4 ,it has become the strange privilege of humanity to contemplate from its little shoal of time the oceanic flow of their development4 ,thus1 in the swing of the ages1 ,laplace's thought was caught up and vitalized4 ,he himself was scarcely sensible of their movement4 ,he recognised very imperfectly1 if at all1 his obligations to ,herschel's nebulous star4 ,his means were inadequate2 his field of view narrow2 his knowledge1 though co-extensive with that of his time1 fell short of what his boundless task demanded4 ,in some respects his mode of procedure was faulty2 his forecasts have been belied2 the behaviour imputed by him to a nebula such as he devised is questionable1 if not impossible4 ,but with the instinct of consummate intelligence he hit off the 'psychological moment1' and1 divining the genetic import of harmonies of construction obvious to perception1 but arduous of interpretation1 he laid down with masterly simplicity the ground-plan of a structure likely to maintain its substantial integrity despite innumerable additions and rectifications4 ,,footnotes3 ,footnote #c3 ,quoted by ,dr4 ,hastie in the preface to his translation of ,kant's ,cosmogony1 ,glasgow1 #aijj4 ,footnote #d3 ,sur l',origine du ,monde1 #c;e d41 p4 #acf4 ,footnote #e3 ,this also was pointed out by ,m4 ,faye1 loc4 cit41 p4 #aej4 ,footnote #f3 ,nature1 ,july #i1 #aijc4 ,footnote #g3 ,rutherford1 ,radio-activity1 p4 #cdb4 ,footnote #h3 ,philosophical ,transactions1 vol4 lxxxi41 p4 #he4 ,footnote #i3 ,herschel met ,laplace during a visit to ,paris in ,july1 #ahja1 but what passed between them is unrecorded4 ,in the sixth edition1 however1 of the ,exposition du ,systme du ,monde1 ,laplace referred to ,herschel's observations of nebul as confirmatory of his own genetic scheme4 ,,chapter ,,iii ,,criticisms ,,of ,,the ,,nebular ,,hypothesis ,laplace's theory was a perfectly definite conception4 ,in this lay its distinctive merit2 in this also its special susceptibility to attack4 ,here was no question of condensation round nuclei arising at discretion amid the large possibilities of boundless elemental confusion2 but of an orderly succession of occurrences1 rendered inevitable by the steady operation of mechanical laws1 and harmonizing1 in their outcome1 with the array of ascertained phenomena visible in the planetary system4 ,these accordingly ceased to be regarded as arbitrary or casual2 they became linked together in the present1 and with the past1 as joint products of one grand scheme of development4 ,the mode of origin of the bodies exhibiting them accounted1 its inventor claimed to have shown1 simply and entirely for them all2 and at least the fundamental propositions laid down by him could not be gainsaid4 ,clearly1 the unanimity of planetary movements is no result of chance2 it represents quite obviously a survival of the general swirl of an inchoate mass1 occupying primitively the whole recognised sphere of solar influence4 ,ambiguities set in only when details come to be considered4 ,the engendering nebula devised by ,laplace was provided with a vast endowment of heat and a slow movement of rotation2 hence cooling1 contraction1 and acceleration advanced pari passu1 the last as a consequence of the mechanical law by which the algebraic sum of the areas described by any number of bodies round a given axis1 multiplied by their several masses and projected upon a single plane1 remains constant to the end of time4 ,in other words1 to repeat what has been stated a few pages back1 the moment of momentum of a congeries of particles can neither increase nor diminish through the effects of their mutual interactions1 however varied and prolonged4 ,the nebula then quickened its pace until a stage was reached at which centrifugal speed could no longer be controlled by gravity2 separation became inevitable1 and an equatorial ring was abandoned1 which thenceforward revolved on its own account in the period conformed to by the undivided mass at the epoch of its secession4 ,this was the first of many subsequent crises of instability1 each eventuating in the detachment of a nebulous ring4 ,these rings1 however1 were regarded as merely transitional forms4 ,they survived1 just for illustrative purposes1 in the ,saturnian system2 elsewhere they broke up into fragments1 which ultimately coalesced into globes1 and the globes were embryo planets4 ,there was1 indeed1 a hitch in the line of argument which did not escape the acumen of the ,french geometer4 ,the direction of the axial movement imparted to the members of the solar family depended essentially upon the relative velocities of the portions of matter brought together for their construction4 ,if the inner sections of the self-shaping mass moved faster than the outer1 the resulting rotation should have been retrograde2 if slower1 direct rotation would have ensued4 ,now1 in a ring like that of ,saturn1 composed of discrete particles1 linear speed decreases continuously outward1 each of its minutest constituents obeying independently ,kepler's law of periods and distances4 ,such a formation1 since it would necessarily have yielded backward-spinning planets1 would have been unfit for the purpose in view1 and ,laplace accordingly substituted an annulus endowed with a considerable amount of cohesion1 and capable of rotating1 like a solid1 in a single period4 ,it is true that such unanimity of movement was incompatible with the other postulated conditions2 but the anomaly escaped notice for above half a century4 ,professor ,darwin has moreover pointed out#aj that a ring of matter distributed with any approach to uniformity must concentrate1 if at all1 round its own centre of gravity4 ,it should accordingly collapse upon1 and become re-absorbed by1 the parent-body4 ,if markedly unsymmetrical and ill-balanced1 its materials might certainly collect at an interior point more or less remote from the centre2 but in no case could the focus of condensation be situated in any part of the annular circumference1 where it was located by ,laplace4 ,whether workable or not1 the genetic plan traced out by him was a strictly regulated one2 its steps were marked with characteristic precision4 ,yet by this very determinateness it gave hostages to the future4 ,it challenged the application of tests which designs more vaguely sketched might have evaded4 ,the primary criterion of its truth was the prevalence of concordant motion throughout the solar domain4 ,counter-currents were formally excluded2 their possibility was not even contemplated4 ,hence1 the discovery of the retrograde systems of ,uranus and ,neptune flatly contravened its pretensions to unconditional acceptance4 ,with less evidence1 but equal certainty1 ,laplace's hypothesis1 strictly interpreted1 involves the consequence that each planet circulates in the identical time occupied by the rotation of the undivided nebula just before instability toppled over into separation4 ,each of the planetary periods should accordingly bear a certain ratio1 prescribed by inexorable mechanical law1 to the actual period of the sun's rotation4 ,in point of fact1 however1 the periods in question are much shorter than comports with the necessity for the conservation from age to age of the system's moment of momentum4 ,the discrepancy was adverted to nearly half a century ago by ,m4 ,babinet4#aa ,he showed in ,march1 #ahfa1 that the axial movement of the solar mass1 when distended to fill the sphere of ,neptune1 should have been1 by the law of areas1 so excessively slow that more than #bg1jjj centuries would have been needed for the completion of a single rotation2 while the period1 even when the shrinking nebula had come to be bounded by the terrestrial orbit1 must still have been protracted to #c1aha years4 ,under these circumstances1 centrifugal force would never have overbalanced central attraction2 no rings could have separated1 and no planets could have been formed4 ,quite recently1 ,mr4 ,f4 ,r4 ,moulton1 of ,chicago1#ab has reconsidered the subject in the course of a careful and candid discussion of the difficulties besetting the nebular cosmogony as viewed from the standpoint of modern science1 and he comes to essentially the same conclusion4 ,his calculations1 though founded on data expressly chosen so as to give the classic theory the benefit of every doubt1 made it perfectly clear that the moment of momentum of the embryo planetary system should have exceeded its present value no less than #bac times if1 when it extended to the distance of ,neptune1 it rotated in what is now the period of ,neptune4 ,but moment of momentum is a constant4 ,the lapse of millions of years makes no difference to it2 it is not1 like energy1 subject to 'dissipation'2 it can neither have gained nor lost value since the sky was first flecked with the 'breath-stain' appointed to condense into our sun1 which1 in this respect at least1 must at every stage of its subsequent evolution have maintained immutability4 ,on the other hand1 this being so1 its primeval wheeling motion would have been much too leisurely to permit the occurrence of accesses of instability4 ,gravity would have steadily kept its supremacy over the forces tending to disruption until the nebula had contracted to less than the compass of the ,mercurian sphere1 and its overthrow at that epoch would have been too late for the origination of any of the sister orbs of the earth4 ,these results1 it is true1 depend in part upon the mode of variation in density ascribed to the progressively shrinking nebula2 but the law adopted by ,mr4 ,moulton has a consensus of authorities in its favour4 ,nor could its deviation from exactitude--if it be inexact--possibly suffice to account for the enormous discrepancies which calculations based upon it have brought to light4 ,the nebular hypothesis stipulates further that satellites must revolve more slowly than their primaries rotate4 ,the reason is patent4 ,in the periodic time of a body detached by centrifugal acceleration the rate of gyration of the original mass is1 if the theory be valid1 perpetuated4 ,subsequent contraction tends to quicken1 and very greatly to quicken1 the rotation of the planet1 while the period of the satellite survives unaltered as a standing record of what the joint period was4 ,this relation may indeed be modified by the effects of tidal friction1 but it is more than doubtful whether it can ever be reversed4 ,it is1 then1 a characteristic feature of the mode of evolution described by ,laplace that no month--so to call it--can be shorter than the corresponding day4 ,and the rule is conformed to in nearly every part of the solar system4 ,nevertheless1 two flagrant violations of it have lately obtruded themselves upon notice1 and can scarcely be explained away by supplementary hypotheses4 ,the first ascertained anomaly of the kind was met with in the swift circulation of ,phobos1 the inner satellite of ,mars1 which completes three revolutions and enters upon a fourth while the planet attended by it wheels once on its axis4 ,the fact is most perplexing1 and the confident persuasion that solar tidal friction would avail to remove the difficulty has not proved well grounded4 ,solar tidal friction1 it may be remarked1 acts as an external force upon subordinate systems submitted to its influence4 ,within their precincts moment of momentum may be destroyed by it2 it tends1 so far1 to abrogate the law of conservation2 and the supposition was hence feasible that the rotation of ,mars had1 in the course of ages1 greatly slackened through the retarding effect of sun-raised tides4 ,but the agency was demonstrably inadequate to the task assigned to it4 ,the reduction of the rotational moment of ,mars to about one twenty-fifth its primitive amount#ac would have brought other consequences in its train1 at least one of which did clearly not ensue4 ,at an early stage of the process ,phobos should have been re-engulfed in the mass of its primary4#ad ,for the pull of the small tidal wave raised by it on the surface of that body would have been backward from the instant that the balance of periods became inclined1 through solar compulsion1 in a direction contrary to that it would have naturally taken2 and the ensuing loss of velocity must have entailed the descent of the little satellite along a spiral path towards an inevitable doom4 ,its continued existence1 then1 closes this way of escape from the difficulty raised by the shortness of its period4 ,m4 ,wolf had recourse to a different explanatory subterfuge4#ae ,he believed that ,phobos might have owed its origin to one of ,roche's 'elliptic sheddings' of nebulous matter dropped downward from near the polar regions of the distended ,martian spheroid1 and rotating1 owing to its low rate of linear speed1 in the immediate vicinity of the cooling planet4 ,the explanation1 though ingenious1 is too recondite to be satisfactory4 ,the mind takes no grip of it2 it evades distinct apprehension4 ,the ,saturnian system exhibits a case of the same kind1 but still more perplexing to speculative prepossessions4 ,saturn's ring-system has always appealed to thinkers as a striking object-lesson in nebular development4 ,it forcibly arrested ,kant's attention1 and he sketched its birth-history on lines anticipatory of those adopted by ,laplace for the solar system in its entirety4 ,laplace himself regarded the formation as the one surviving relic of the annular stage of planet-building--as a witness from the dim past to a condition of things elsewhere transitory4 ,yet the witness has turned king's evidence1 and betrayed the whole situation4 ,the innermost ,saturnian ring has a period far too short to be compatible with the requirements of theory4 ,for its meteoric constituents1 known on spectroscopic testimony to revolve each on its own account1 complete their circuits in between five and six hours1 while the planet needs just ten hours and a half for its axial rotation4 ,moreover1 tidal friction is here far less available than on ,mars2 yet no other retarding agency has been invented4 ,the deadlock appears final and hopeless4 ,an objection quite as formidable1 and even more fundamental1 was raised by ,kirkwood in #ahfi4 ,the nebulous material of the uncondensed sun must have been1 at the outset1 of the utmost tenuity4 ,atmospheric air is1 by comparison1 a dense and massive substance4 ,yet no reasonable person could ascribe to aerial matter the least power of resisting strain4 ,we know perfectly that a rotating globe of air1 and1 fortiori1 a globe of matter thousands of times less compact than air1 would unintermittently disintegrate at the surface with the progress of acceleration4 ,the disturbance and restoration of equilibrium would be virtually simultaneous4 ,there could be no accumulation of internal stress1 and consequently no definitely separated epochs of instability4 ,at the first solicitation1 at the first instant that centrifugal velocity gained the upper hand over gravity1 nebulous wisps would have become detached1 and their detachment would have gone on without pause4 ,space would have been strewn with the dbris of the condensing nebula1 and there should have resulted a vast cloud of cosmic dust1 not a majestic array of revolving spheres4 ,further1 the possibility of their emergence from pre-existent annuli is by no means assured4 ,even if the nebulous material had possessed the fabulous cohesion indispensable for its division into voluminous rings with wide intervening empty gaps1 their ultimate agglomeration into planetary globes would probably never have been effectually accomplished4 ,kirkwood long ago questioned the feasibility of the process4 ,mr4 ,moulton has gone far towards demonstrating that it must have had an abortive outcome4 ,professor ,darwin pronounces its very inception1 apart from very special conditions1 to be impracticable4 ,another grave objection to ,laplace's scheme is founded on the marked deviations visible in the solar system1 from conformity to a fundamental plane of motion4 ,unless acted on by influences difficult to imagine or explain1 all the planets should circulate along the level of the sun's equator1 and rotate on axes perpendicular to it4 ,how far this is from being realized in nature we have only to look around us to perceive4 ,we owe the changes of our seasons to the tilted fashion of the earth's spinning4 ,yet it is by no means easy to understand how the pole of its equator comes to be situated in the tail of ,ursa ,minor1 while the pole of the ecliptic is involved in the folds of ,draco4 ,they should have coincided if the simple rules of the nebular prescription had been followed in the making and modelling of the planets4 ,nor are the terrestrial arrangements exceptional4 ,the ,saturnian equator and the ,saturnian rings have a still higher inclination2 while in the systems of ,uranus and ,neptune--if we may thus interpret their retrograde revolutions--the angle exceeds the limit of a quadrant4 ,these and other similar discrepancies prove the solar mechanism to have originated by a more complex method than that imagined by ,laplace1 and an hypothesis which invokes the aid of a multitude of auxiliary devices for its extrication from accumulating embarrassments falls thereby under the suspicion of not being worth the trouble of extricating4 ,it forfeits1 at any rate1 all claim to commendation for directness and simplicity4 ,the cosmogony turned out at ,paris has thus proved vulnerable on a number of points2 but all the blows aimed at it have not told with such deadly effect as those just referred to4 ,some have fallen harmlessly1 or glanced aside4 ,one hostile argument in particular1 which for a time seemed irresistible1 has been completely overthrown by the logic of facts1 and deserves mention only as a historical curiosity4 ,towards the middle of the nineteenth century the progress of sidereal astronomy seemed to take the direction of showing all nebul indiscriminately to be of stellar composition4 ,with ,lord ,rosse's great reflectors a good many such objects were genuinely1 and some besides were deceptively1 resolved into stars1 the illusory effects being confirmed by ,bond's observations with the deservedly celebrated #ae-;inch refractor then recently built by ,merz for ,harvard ,college4 ,hence the rash inference was drawn that resolution was wholly a question of optical power1 and that no real distinction existed between the stellar and the nebular realms4 ,herschel's 'shining fluid' assumed a mythical air2 'island-universes' came into popular vogue2 and all but a few careful thinkers held nebul and clusters to be differentiated merely by degrees of remoteness4 ,but if space contained only full-grown stars and no stars in the making--no star-spawn1 no star-protoplasm--then the imagined evolutionary history of our system was left in the air1 destitute of even the most fragile prop of observed fact4 ,from this precarious position it was rescued1 partly by the cogent reasonings of ,whewell and ,herbert ,spencer1 finally and triumphantly by ,sir ,william ,huggins's spectroscopic discovery of the cosmic gas 'nebulium4' ,since ,august1 #ahfd1 there has been no possibility of denying that the heavens contain ample stores of just the kind of material ,laplace wanted1 though whether it played just the part he assigned to it in the manner that he supposed is a question to be answered with profound and growing reserve4 ,an objection of late urged against the nebular theory from the standpoint of the kinetic doctrine of gaseous constitution is of much speculative interest4 ,a gaseous nebula equal in mass to the sun and planets1 and distended sufficiently to fill the orbit of ,neptune1 would have been1 supposing the prevalent opinion correct1 subject to a rapid leakage into space of its lighter ingredients4 ,of hydrogen and helium1 we are told1 it should infallibly have become depleted2 yet there is no lack of either in the sun of the twentieth century4 ,their retention1 it must be admitted1 is1 on the hypothetical conditions1 difficult to account for4 ,the 'critical velocity' at the limiting surface of the supposed nebula would have been #dh miles a second4 ,this is1 in fact1 at the distance of ,neptune1 parabolic speed4 ,the planet itself1 if it could attain to it1 would break the bonds that bind it to the sun1 and seek its fortunes under some different allegiance4 ,similarly1 any particle of the primitive nebula thus accelerated should have become an irreclaimable vagrant4 ,now1 the velocity of hydrogen molecules at the zero of ,centigrade is1 in the mean1 about #a-a_/f miles a second1 but attains in the extreme to above seven miles4 ,hydrogen could not then have been permanently retained by the solar nebula1 and the escape of helium would have more slowly ensued4 ,yet these results1 though seemingly inevitable1 did not actually come to pass1 either because the generating body was differently constituted from what has been supposed1 or because countervailing influences were brought to bear4 ,it is1 for instance1 amply possible that the dynamical condition of gases may be essentially modified by rarefaction carried to a degree transcending the range of experimental enquiries4 ,the progress of science affords many warnings against trusting implicitly to the rule of continuity4 ,curves of change seldom preserve indefinitely a uniform character4 ,their unexplored sections may include quite unlooked-for peculiarities of flexure1 and the possibility seriously undermines confidence in inferences depending upon 'extrapolation4' ,the presence of hydrogen and helium in our system cannot1 then1 be ranked among facts incontestably contradictory of the nebular hypothesis4 ,the concerted advance of mathematical astronomy during the eighteenth century was effected with the confident serenity of irresistible power4 ,one after another the obstacles barring its path went down before repeated and skilful onslaughts1 the unbroken succession of which lends a certain exultant sameness to the story of the heroic age of analysis4 ,the ,mcanique ,cleste attested 'victory all along the line4' ,there were no more worlds to conquer that ,laplace knew of2 the reign of gravitational law was firmly established throughout the solar dominions2 menaced revolts had been appeased2 anomalies removed2 no extant observations any longer impaired the perfect harmony between what was and what had been foreseen4 ,nature for the moment submitted readily to the trammels put upon her by human thought2 her intricacies had apparently ceased to defy unravelment2 her modes of procedure looked straightforward and intelligible4 ,as they were judged to be in the present1 so they might be presumed to have been in the past2 and the temptation was irresistible to adventure backward speculation1 inferring initial conditions from the elaborated product laid open to scrutiny4 ,it was an epoch of peremptory renewals4 ,the formula of equality promised to regenerate society2 a political panacea had been found by the creation of a republic 'one and indivisible'2 and the success of the guillotine in securing its supremacy was almost outdone by the triumphs of the calculus in vindicating the unimpeded sway of gravitation4 ,humanity had made a fresh start2 science should do likewise4 ,the sanguine spirit of a rejuvenated world animated all forms of human endeavour4 ,it has long since evaporated4 ,the buoyant hopes of a century back have been crushed2 the future of civilization looks dim2 and its uncertainty compromises the future of knowledge4 ,but we1 at any rate1 no longer delude ourselves with the idea that he who runs may read the secrets of the universe4 ,we have learned by convincing experience how much1 and how variously1 'the subtlety of nature transcends the subtlety of sense and intellect'2 we are vividly aware that there is no single and simple recipe for the 'cosmification' of chaos4 ,that devised by ,laplace has ceased to be satisfactory4 ,its simplicity1 at first sight so seductive1 leaves it at a disadvantage compared with the intricacy of the effects it was designed to elicit4 ,the relations claiming explanation have multiplied with the progress of research4 ,those of the dynamical order were alone attended to by the geometers of the eighteenth century1 and even they have grown recalcitrant2 while those of a physical and chemical kind have proved wholly unmanageable4 ,it has1 indeed1 become abundantly clear that the series of operations described by ,laplace could scarcely1 under the most favourable circumstances1 have been accomplished1 and in a thin nebulous medium would have been entirely impossible4 ,the nebular cosmogony has not1 then1 stood ',foursquare to all the winds that blew4' ,its towers and battlements have crumbled before the storms of adverse criticism4 ,it survives only as a wreck1 its distinctive features obliterated1 although with the old flag still flying on the keep4 ,in the next chapter we shall attempt a survey of the works set on foot for its reconstruction4 ,,footnotes3 ,footnote #aj3 ,presidential ,address to the ,british ,association1 ,johannesburg1 ,august #cj1 #aije4 ,footnote #aa3 ,comptes ,rendus1 tom4 lii41 p4 #dha4 ,footnote #ab3 ,astrophysical ,journal1 vol4 xi41 p4 #ajc4 ,footnote #ac3 ,moulton1 ,astrophysical ,journal1 vol4 xi41 p4 #aaj4 ,footnote #ad3 ,nolan1 ,nature1 vol4 xxxiv41 p4 #bhg4 ,footnote #ae3 ,bulletin ,astronomique1 tom4 ii41 p4 #bbc4 ,,chapter ,,iv ,,the ,,nebular ,,hypothesis ,,varied ,,and ,,improved ',restorations' often go very far4 ,things may be improved beyond recognition1 nay1 out of existence4 ,so it has happened to the nebular hypothesis4 ,stat nominis umbra4 ,the name survives1 but with connotations indefinitely diversified4 ,the original theme is barely recalled by many of the variations played upon it4 ,entire license of treatment prevails4 ,the strict and simple lines of evolution laid down by ,laplace are obliterated or submerged4 ,some of the schemes proposed by modern cosmogonists are substantially reversions to ,kant's ,natural ,history of the ,heavens2 the long-discarded and despised ,cartesian vortices reappear1 with the clat of virtual novelty1 in others2 nor are there wanting theories or speculations reminiscent even of ,buffon's cometary impacts4 ,moreover1 the misleading fashion has come into vogue of bracketing ,kant with ,laplace as co-inventor of the majestic and orderly plan of growth commonly designated the 'nebular hypothesis4' ,this has been1 and is1 the source of much hurtful confusion4 ,save the one fundamental idea--and that by no means their exclusive property--of ascribing unity of origin to the planetary system1 ,kant's and ,laplace's evolutionary methods had little in common4 ,their postulates were very far from being identical2 they employed radically different kinds of 'world-stuff'2 and the 'world-stuff' was subjected1 in each case1 to totally dissimilar processes4 ,yet it is often tacitly assumed that to defend or refurbish one scheme is to rehabilitate the other4 ,under cover of the intellectual vagueness thus fostered1 a backward drift of thought is1 indeed1 discernible towards the view-point of the ,knigsberg philosopher4 ,it is recommended1 not so much by the favourable verdict of science as by the wide freedom of the prospect which it affords4 ,the imperative guidance of ,laplace1 reassuring at first1 led to subsequent revolts4 ,but ,kant is highly accommodating2 one can deviate widely from1 without finally quitting1 the track of his conceptions2 they are capacious and indefinite enough to comport with much novelty both of imagination and experience1 and hence lend themselves with facility to the changing requirements of progress4 ,a noteworthy attempt was made1 in #ahgc1 by the late douard ,roche of ,montpellier to reconstruct1 without subverting1 ,laplace's hypothesis4 ,this remarkable man lived and died a provincial4 ,only a few scattered students have made acquaintance at first hand with his works2 his fame1 always dim1 now already begins to seem remote4 ,yet a score of years ago he was still lecturing at the ,lyce of his native town4 ,the waters of oblivion have grown1 perhaps1 more turbid than of yore4 ,anyhow1 ,roche of ,montpellier is only vaguely remembered1 and that by a specially educated section of the public1 as having fixed a limit within which a satellite cannot revolve intact4#af ,nearer to the ruling planet than #bdd of its mean radii1 it could not--setting aside improbable conditions of density--maintain a substantive globular status under the disruptive strain of tidal forces4 ,in point of fact1 all the moons so far discovered in the solar system circulate outside ',roche's limit'2 and ,saturn's rings1 which lie within it1 owe to that circumstance1 it may plausibly be asserted1 their pulverulent condition4 ,professor ,darwin accordingly regards knowledge of that condition as dating from #ahdh1 the year in which ,roche published the law involving it as a corollary4#ag ,roche was the precursor of ,poincar and ,darwin in those profound investigations of the figures of equilibrium of rotating fluid bodies which have opened up new paths and disclosed untried possibilities in evolutionary astronomy4 ,his researches1 moreover1 into the origin of the solar system#ah constituted a reinforcement of first-rate importance to the strength of ,laplace's position4 ,he was perhaps its most effective and timely defender2 he came to the rescue just when its safety was seriously compromised1 repaired its breaches1 and threw up skilfully constructed outworks4 ,adopting the same premisses1 he drew virtually the same conclusions as ,laplace1 ingeniously modifying them1 however1 so as to evade certain objections1 and temporarily to silence the less obstinate cavillers4 ,his results were1 indeed1 almost as difficult to disprove as they had been to attain4 ,they were arrived at laboriously1 legitimately1 by long-drawn analytical operations2 and the reasonings survive in full credit1 even although the initial conditions they started from now wear an aspect of unreality4 ,thus1 the invention of traines elliptiques not only usefully met an argumentative emergency1 but still remains as a supplementary adjunct to cosmic processes4 ,undeniably1 polar annulation may have played a part in planetary formation2 the possibility cannot be gainsaid4 ,the 'ellipsoidal trains' investigated at ,montpellier were huge nebulous strata detached from the polar regions of the primitive spheroid1 which1 bringing with them the low rotational velocity proper to that situation1 tended1 some to constitute interior equatorial rings1 others to become agglomerated with the central mass4 ,but their incorporation should have had as its consequence--since the 'law of areas' is inviolable--a quickening of angular rotation throughout the nebula4 ,the 'law of areas1' it may be explained1 is merely a short title for the 'law of conservation of moment of momentum1' which prescribes--as we know--that the sum total of the areas described in a given time on a given plane by the members or constituent particles of a rotating system1 multiplied by their several masses1 remains constant under all conceivable circumstances of re-arrangement or mutual disturbance4 ,hence1 approach towards the centre1 because it narrows the circle1 must quicken the speed of rotation4 ,a short line having to sweep over the same space as one of greater length1 its moving end must proportionately hurry its pace4 ,an engulfment1 accordingly1 by the embryo sun of one of ,roche's 'elliptic trains' would have occasioned an immediate shortening of the period of revolution of both nucleus and atmosphere1 an accession of centrifugal force producing sudden instability1 and1 as a consequence1 the separation of an equatorial ring4 ,by this subtly devised expedient ,roche sought to explain away the difficulty connected with the wide intervals between the planets4 ,for they originated1 he conceived1 not in the regular course of condensation1 but through complications arising abruptly and exceptionally4 ,what he called the 'limiting surface' of the nebula might also be described as the atmospheric limit4 ,it corresponds to the widest possible extension of a true atmosphere4 ,its boundaries are fixed at the distance just outside of which a satellite could freely circulate in the axial period of its primary4 ,now the limiting surface1 if contraction had proceeded equably1 should have retreated continuously1 as axial movement quickened1 its withdrawal being attended by the shedding of slender rivulets of superfluous matter4 ,but by the introduction of 'elliptic trains1' stability1 artificially maintained 7so to speak7 throughout long spells of time1 was overthrown only by catastrophic downrushes from the shoulders of the nebulous spheroid1 when1 with the prompt abridgment of the axial period1 the limiting surface as promptly shrank inward1 and there was left1 outstanding and self-subsistent1 the tenuous ring destined to coalesce into a planet4 ,a singular and unexplained felicity of ,roche's analysis consisted in the symmetry of time-relations established by it4 ,the successive births of his planets followed each other at equal intervals4 ,a species of translation of ,bode's law of distances 7extended by him to satellite-systems7 in terms of the nebular hypothesis thus appeared to be rendered feasible4#ai ,that hypothesis1 in its original form1 as explained in the last chapter1 produced planets with retrograde rotation--that is1 spinning in an opposite sense to that of their circulation4 ,for the purpose of abolishing the anomaly1 ,kirkwood1 in #ahfd1bj had recourse to solar tidal friction1 and he was followed1 doubtless independently1 by ,roche1 and by ,roche's interpreter1 ,c4 ,wolf of ,paris4 ,objections to any particular mode of planetary formation1 on the ground that its outcome must have been inverted axial movement1 lost their validity1 they remarked1 through the consideration that solar tidal friction would have availed to redress the incongruity4 ,for its retarding action would have ceased only when synchronism with the revolutionary period was attained--that is1 when the planet wheeled in its orbit1 as ,mercury seems to do1 turning always the same face inward2 and then already direct rotation would have set in1 and1 becoming accelerated by contraction1 should permanently retain the direction impressed upon it by the friction of sun-raised tides4 ,a certain air of plausibility is given to this view by the fact that the only two retrograde planetary systems are situated entirely beyond the possible range of any such manner of influence1 and may accordingly be supposed to have preserved unaltered their primitive fashion of gyration4 ,the late ,m4 ,faye was less loyal to tradition than the savant of ,montpellier4 ,the appearance in #ahhd of his work1 ,sur l',origine du ,monde1 gave the signal for renewed activity and a larger license in cosmological speculation4 ,conservative opinions on the subject are now rarely held2 the old groove has been by most definitively quitted2 inquiry becomes continually more individual and less constrained by tradition4 ,faye's reform1 however1 was not avowedly of a revolutionary character4 ,he did not make a clean sweep of the work of his great predecessor1 by way of preliminary to setting forth his own more perfect plan4 ,yet his emendations of it went very deep4 ,laplace's nebula was of a gaseous consistence1 and it stood in a genuine atmospheric relation to the central condensation--that is to say1 its strata gravitated one upon the other2 they were subject to hydrostatic pressure4 ,faye ruled things otherwise4 ,the nebulous matrix which he postulated was a vast congeries of independently moving particles1 forming a system governed by a single period1 in which both gravity and velocity increased in the direct ratio of the distance from the centre4 ,now1 globes formed by the method of annulation 7admitting its practicability7 out of materials thus conditioned1 should have possessed1 ab initio1 a direct rotation2 their axial spinning would have been in the same sense as their orbital circulation4 ,and this it was which recommended to ,faye the adoption of a meteoric structure for the inchoate solar system4 ,but the simple law of force regulating it at first would1 by degrees1 have undergone essential alteration4 ,that of inverse squares1 familiarized to ourselves by long habits of thought1 would have begun to supersede it so soon as a sun1 properly so called1 could be said to exist4 ,the retrograde planets1 ,uranus and ,neptune1 must1 however1 by ,faye's supposition have taken shape under the modern regimen2 they were formed subsequently to the earth and all the rest of her sister orbs4 ,this unexpected inversion of the recognised order of planetary age involved the further consequence that the ante-natal offspring of the sun--thus paradoxically to designate them--must have drawn closer to him as his attractive power developed1 ,uranus and ,neptune alone among the entire cortge preserving the original span of their orbits4 ,faye's scheme1 if it did not meet all the arduous requirements of the problem it confronted1 served1 at any rate1 to illustrate very forcibly the devious variety of tracks by which nebular evolution might advance towards its goal4 ,the particular one chosen was certainly not clear of impediments4 ,in his preoccupation with the removal from ,laplace's hypothesis of the flaw relating to planetary rotation1 ,m4 ,faye had discarded its cardinal merit of explaining secessions of material by the growth of centrifugal force4 ,he alleged no sufficient reason1 and none could be alleged why the remodelled nebula should have separated into rings4#ba ,the process implies definite and special conditions2 it testifies to a rhythmically acting cause4 ,laplace brought such a cause into play4 ,faye abolished it1 and his annuli1 accordingly1 wear a fictitious aspect4 ,it is1 indeed1 true that an annular structure is commonly visible in nebul1 but it is begging a most arduous question to assume that nebular spires have anything in common with planet-forming rings4 ,these would probably never have been heard of save for the ,saturnian example4 ,a pattern is easily copied2 an idea palpably feasible is tempting to adopt2 a demonstration on the solvitur ambulando principle cannot but prove convincing4 ,but how if the rings cannot be made to coalesce into globes8 ,and the difficulty of the transformation becomes more apparent the more clearly its details are sought to be realized4 ,reversed in direction1 it might better find a place in the order of ,nature4 ',analysis seems to indicate1' ,kirkwood wrote in #ahhd1bb 'that planets and comets have not been formed from rings1 but rings from planets and comets4' ,nor is this mode of procedure merely possible according to theory2 it is also vividly illustrated by facts4 ,meteoric swarms can be observed1 decade by decade1 to disperse under the scattering influence of the sun and planets1 and unmistakably tend to become more or less uniformly distributed along the entire round of their orbits4 ,their advance is directed1 not towards condensation1 but towards disaggregation2 and they pursue it with surprising rapidity4 ,faye's theory was disfigured by a still more glaring incongruity4 ,nothing in the planetary economy seems more evident than that the zone of asteroids marks a division between two strongly dissimilar states of the solar nebula4 ,it is a visible halting-place4 ,one series of events came to an end1 and there was an interlude before the next began4 ,during that interlude1 during the partial suspension of activity which ensued upon the production of the ,ajax among the planets1 the crowd of planetoids were launched to fill the blank space4 ,here1 if anywhere1 ,nature changed her hand and tried a fresh method4 ,faye's shifting of the scene of change to trans-,saturnian regions is then1 as ,m4 ,wolf justly perceived1 non-natural1 and undermines the credit of a plan to which the device is essential4 ,on the other hand1 it had the merit of being elastic enough to include the great cometary family4 ,kant had also1 although in an unsatisfactory manner1 made room for them2 but ,laplace had no choice save to regard them as casual intruders from space1 the admission of which as natives of his well-ordered domain would have led to the subversion of all its harmonious regulations4 ,modern inquiries1 however1 prove comets decisively to be no such stray visitors as ,laplace supposed1 but to be of the same lineage--however remotely traceable--with the planets1 and to own the same allegiance4 ,drifting with the sun1 they form part of its escort on the long1 irrevocable voyage it is engaged upon1 and cannot1 save by accidents of perturbation1 be driven finally to part from its company4 ,the problems of planetary and cometary origin are then inseparable2 the two classes of body are fellow-citizens of one kingdom4 ,comets become only by compulsion cosmopolitan wanderers from star to star4 ,there was yet another motive and semblance of justification for ,faye's reform of the nebular hypothesis4 ,the discovery of the conservation of energy supplemented1 as we have seen1 very happily the mechanics of a condensing nebula by satisfactorily solving the enigma of solar radiation4 ,helmholtz was thus able1 in #ahga1 to sketch cosmic development as1 in its essence1 a thermodynamic process on the grandest scale4 ,yet the alliance entered into1 fruitful and fortifying though it was1 had an attendant embarrassment4 ,time had now to be reckoned with4 ,in the cosmogonies of ,kant1 ,herschel1 and ,laplace the allowance of ons was unstinted4 ,because the rate of change was indeterminate1 they might be permitted to elapse ad libitum4 ,but it was otherwise when the driving-power came to be defined4 ',conservation of force' implies the measurableness of force4 ,equivalence cannot be ascertained where no limits are determinable4 ,knowledge1 accordingly1 regarding the source of the sun's heat brought with it the certainty that the source was by no means inexhaustible4 ,the stock of energy rendered available by shrinkage from a primitively diffuse to its present compact state was enormous1 but not boundless4 ,the task then became incumbent upon cosmogonists of proving its sufficiency1 or of eking out its shortcomings4 ,the problem is both retrospective and prospective4 ,we look back towards the birth of the sun1 we look forward to its demise2 and each event has1 if possible1 to be located on our time-scale4 ,helmholtz assigned terms of twenty-two millions of years in the past and seventeen millions in the future for the shining of our luminary with its actual intensity4 ,geologists and biologists1 however1 claimed a much more extended leisure for the succession of phenomena on this globe1 and efforts on the part of physicists to meet their demands barely availed to tone down without removing the discrepancy4 ,m4 ,faye then came to the rescue4 ,his suggestion that the earth took separate form while the sun was still nebulous was designed to conciliate the demands of those who needed all but eternity for the slow accumulation into specific differences of infinitesimal variations4 ,in this way a start was gained upon the sun2 the preparations for vitality on our planet were going forward long before the lavish radiative expenditure designed to nurture its development had begun4 ,the earth1 in fact1 was shaping itself for its destiny in advance of the epoch when time began to count for the sun4 ,this supposed relation of precedence cannot1 indeed1 be insisted upon2 it was imagined to save a difficult situation1 and intimates a design more or less academic4 ,yet the expedient was significant as regards the effect of the introduction into modern thought of the principle of the conservation of energy4 ,it gave definiteness and a kind of solidity to speculation by widening the basis upon which it was made to rest4 ,at the same time it necessitated adjustments between the exigencies of the various sciences1 and brought into prominent view apparent incompatibilities only to be removed by prolonged investigations of wide scope and intricate bearings4 ,modern cosmogony1 in short1 while disposing of enlarged means1 has to meet multiplied requirements4 ,quite lately1 nevertheless1 some authoritative exponents of geological and biological science manifest a satisfactory disposition to 'hurry up their phenomena1' quite independently of the inadequate age of the sun4#bc ,on neither side1 accordingly1 are the irreconcilable claims of the past any longer insisted upon1 and a compromise has become easily possible4 ,a theory of planetary evolution marked by some novel features was ably expounded by ,m4 du ,ligonds in #ahig4bd ,designed to improve1 by simplifying1 ,faye's plan1 it reduced postulates to a minimum1 and left the freest possible play to 'original indetermination4'#be ,the embryo world of ,m4 du ,ligonds was a tumultuous mle of particles moving anyhow4 ,their jostlings1 however1 did not1 and could not1 exactly balance1 and the inequality1 small though it might be1 sufficed to afford a basis for harmonious growth4 ,motion became regularized by collisions2 counter-currents of velocity were gradually eliminated2 and the particles pursuing eccentric or retrograde courses1 brought sooner or later to a stand1 fell towards the centre and accumulated into the sun1 while the remnant that travelled in the prevalent direction along circular paths finally constituted the planets4 ,they were formed1 not at haphazard1 but through the medium of zones of maximum density1 due to the variations of gravity within the disc towards which the primitive spheroid finally collapsed2 and each1 as it took shape1 became a source of perturbative influence on its subsequently developed neighbours1 by which the inclinations of their orbital planes and of their axes of rotation were in various ways altered4 ,the planetary zones1 too1 contracted with the advance of condensation1 so that the matured planets occupied positions much nearer to the sun than those assigned to their inchoate materials4 ,the modus operandi employed1 in short1 adapted itself with praiseworthy readiness to the diversities of nature4 ,sir ,robert ,ball is at one with ,m4 du ,ligonds in regarding the origin of the solar system chiefly under its mechanical aspect4 ,like ,helmholtz and ,faye1 he chooses pulverulent materials to work with2 his nebula is a 'white nebula4' ,but looking still further back1 he discerns as its parent an irregular 'green' nebula1 the confused movements of which falling into a settled order as the result of encounters1 it slowly flattened down into the 'plane of maximum areas'--the fundamental plane conformed to more and more closely as the energy of a system inevitably wastes4 ,he dispenses with the troublesome process of annulation1 and starts his planets virtually by ,kant's method of accidental nuclear condensation4#bf ,a spiral structure1 moreover1 would be imparted to the entire nebula by the gradual propagation outward of the central acceleration due to contraction4 ,but would it have contracted8 ,it had1 by supposition1 reached the stage of approximate unanimity in movement4 ,the great bulk of its constituent bodies circulated in the same direction1 in nearly the same plane1 and presumably in orbits not deviating much from circularity4 ,their aggregate condition might then be regarded as permanent and stable4 ,the central mass would1 accordingly1 no longer be fed by the engulfment of particles brought to rest by their mutual impacts2 motion being unimpeded1 heat could not be evolved2 and the imagined transformation of a disc-like meteoric formation into a sun and planets would fail to come to pass4 ,what1 then1 we may ask ourselves1 is the upshot of these various efforts at reconstruction8 ,they establish1 certainly1 the unassailable unity of the solar world2 and the solar world must be understood to embrace comets and cometary meteors4 ,the arguments favouring this unity have gained enormously in cogency through modern discoveries4 ,for those depending upon structural coincidences and harmonies of movement have been reinforced by others of a totally different nature1 furnished by the doctrine of the conservation of energy and the teachings of spectrum analysis4 ,the sun is hot because it was anciently expanded2 the energy of position formerly belonging to its particles incontestably provided a large part1 if not the sum total1 of its present thermal energy1 and this amounts to saying that a sphere indefinitely great was once filled by our inchoate system4 ,the conclusion that it arose from an undivided whole through the gradual differentiation of its parts is further ratified by the identity of solar and terrestrial chemistry4 ,the earth is thus strongly averred to have once made an integral part of the substance of the sun1 and what is true of the earth is no less true of its sister planets4 ,regarding the mode and manner of cosmic change there is1 nevertheless1 no consensus of opinion4 ,faye made a noteworthy effort to elaborate a process that might endure modern tests of feasibility1 yet his theory has been well-nigh torn to pieces by adverse criticism4 ,m4 du ,ligonds escapes some1 but not all1 of the objections which proved fatal to his predecessor4 ,that there was in the beginning a solar nebula1 all are agreed2 but whether it was gaseous or pulverulent1 whether it shone with interrupted or continuous light1 how it became ordered and organized1 how it collected into spheres1 leaving wide interspaces clear1 the wisest are perplexed to decide4 ,mr4 ,moulton concludes1 from his careful examination of the subject1 that 'the solar nebula was heterogeneous to a degree not heretofore considered as being probable1 and that it may have been in a state' resembling that exhibited in recent photographs of spiral nebul4#bg ,but1 even if all the facts do not chime in with this tempting analogy1 there can be little reason to dissent from his intimated opinion that 'the ,laplacian hypothesis is only partially true1 and that we do not yet know the precise mode of the development of the solar system4' ,,footnotes3 ,footnote #af3 ,mmoires de l',acadmie de ,montpellier1 tom4 i4 ,footnote #ag3 ,the ,tides1 p4 #cbg4 ,footnote #ah3 ,mmoires de l',acadmie de ,montpellier1 tom4 viii4 ,footnote #ai3 ,c4 ,wolf1 ,bulletin ,astronomique1 tom4 i41 p4 #eif4 ,footnote #bj3 ,american ,journal of ,science1 vol4 xxxviii41 p4 #c4 ,footnote #ba3 ,g4 ,h4 ,darwin1 ,nature1 vol4 xxxi41 p4 #ejf4 ,footnote #bb3 ,proceedings of the ,american ,philosophical ,society1 vol4 xxii41 p4 #aji4 ,footnote #bc3 ,de ,vries1 ,die ,mutationstheorie1 ,bd4 ,,ii41 p4 #gad4 ,footnote #bd3 ,formation ,mcanique du ,systme du ,monde4 ,see also ,le ,problme ,solaire1 by the ,abb ,th4 ,moreux1 p4 #fc et seq4 ,footnote #be3 ,revue des ,questions ,scientifiques1 ,january1 #aijd4 ,footnote #bf3 ,the ,earth's ,beginnings1 p4 #bdg4 ,footnote #bg3 ,astrophysical ,journal1 vol4 xi41 p4 #acj4 ,,chapter ,v ,,tidal ,,friction ,,as ,,an ,,agent ,,in ,,cosmogony ,the effects of tidal friction are of almost infinite complexity4 ,how it will act in each particular case cannot be predicted offhand2 it is a matter for detailed inquiry4 ,mutually countervailing influences have to be taken into account1 nor is the balance easy to strike4 ,the manner of its inclination may1 indeed1 often depend upon qualities and relations of the bodies concerned which lie outside the range of what can be distinctly ascertained4 ,all that may be hoped for1 then1 is to arrive at estimates neither misleading by their ostensible precision1 nor yet so vague as to be wholly uninstructive1 of the part played by tidal forces in moulding the history of connected globes4 ,the assumption that they attract one another as if the mass of each were collected at its centre1 is one of those convenient fictions without which the advancing feet of science would be impeded by tangled thickets of illusory refinements and superfluous elaborations4 ,the fiction would correspond with fact only if the globes were truly spherical1 and they could be truly spherical only if they were ideally rigid4 ,cosmic bodies1 however--suns and planets alike--are actually plastic spheroids2 they can1 to be sure1 be treated without sensible error as attractive points when their distances are very great relatively to their diameters2 but upon a closer approach inequality of action supervenes4 ,the component parts of the gravitating masses respond1 each individually1 and in a measure independently1 to the graduated pulls exercised upon them1 and tidal strains begin variously to take effect4 ,their historical significance was in part divined by ,kant4 ,his penetration of so recondite a secret is truly astonishing4 ,a struggling young pedagogue in a remote ,prussian province1 profoundly learned1 though no more than half skilled in technical acquirements1 saw by intuition what escaped the acumen of all the great geometers of the eighteenth century--namely1 that the moon turns one perpetual face towards the earth1 because its primitive rotation was stopped by the friction of earth-raised tides4 ,he perceived besides that a reciprocal action of the same kind must affect the earth1 and will continue to affect it until the day coincides in length with the month4 ,nor did he fail to point out that1 in a molten state of the globes1 the process would advance with comparative rapidity4 ,to one solitary thinker1 then1 it became apparent1 already in #aged1bh that oceanic tides are1 in cosmogony1 of negligible importance compared with bodily tides4 ,there is no substance in nature that will not change its shape through prolonged stress1 and the more readily the nearer it approaches to the fluid condition4 ,the heaping-up of the waters on the earth's surface at the bidding of the moon is thus a differential effect4 ,continents heave and subside as well as oceans1 though not nearly to the same extent4 ,the measurable rise of water serves to gauge the relative mobilities of the solid globe and of its liquid envelope4 ,if the former did not yield at all to the pull so readily obeyed by the latter1 the tides would1 in fact1 be greater than they actually are in the proportion of about three to two1 the ratio indicating for the earth an effective rigidity at least equal to that of steel4#bi ,were there no discrepancy in rigidity between the various parts of our terraqueous world1 tides would fail to be perceptible4 ,the ocean and the bed of the ocean would rise and fall together1 and to the same extent4 ,in the far past there was no discrepancy4 ,the viscous earth took1 as a whole1 the form momentarily impressed upon it by the unequal attractions of the sun and moon on its variously distant sections1 with the upshot of bringing the year1 month1 and day into relations so familiar as to appear inevitable4 ,tidal friction does not merely act as a check upon rotational speed4 ,one element of motion in a system cannot be altered without some counter-change in the others4 ,they are coupled up together like a train of geared wheels4 ,from the principle of the conservation of moment of momentum1 we know with certainty that a loss in one direction must be compensated by a gain in some other4 ,tidal friction had1 then1 reactive consequences4 ,they were first adverted to by ,julius ,robert ,mayer in #ahdh1cj and were brought prominently into view in the series of investigations begun by ,professor ,darwin in #ahgi4 ,the rotational momentum removed from the earth by the drag of a circulating wave of deformation must assuredly have reappeared in some other part of the system4 ,it was restored1 all but the percentage wasted as heat1 by the widening of the lunar orbit4#ca ,concomitantly with the slackening of the earth's axial rate1 the moon retreated from its surface1 pulled forward by the tidal crest continually in advance of its position4 ,this redressed the balance by augmenting orbital momentum1 while at the same time diminishing the moon's linear velocity4 ,the importance of this secondary frictional effect in the history of the earth-moon system was the virtual discovery of ,professor ,darwin4 ,that system occupies a critical situation in the solar cortge4 ,the planets interior to it have no satellites2 the planets exterior to it 7,neptune making probably only an apparent exception to the rule7 have two or more4 ,the earth alone is truly binary2 and the moon is not only its solitary companion1 but it is by far the largest companion-body1 relatively to the mass of its primary1 to be found within the precincts of the solar domain4 ,these circumstances are certainly not disconnected one from the other1 and they obviously depend upon a single cause4 ,solar tidal friction was here the determining factor4 ,the apportionment of satellites to the various planets was1 beyond doubt1 in great measure prescribed by the degrees of retarding power exerted on their axial movement through the agency of sun-raised tides in their still plastic bodies4 ,hence1 the disruptive rate of spinning needed for the separation of satellites was never attained by either ,mercury or ,venus2 they remained moonless for all time1 and exposed1 through the cutting down of their rotational velocity1 to uncompensated extremes of temperature4 ,how the earth was to fare in both respects long hung in the balance4 ,rightly to forecast its destiny would1 indeed1 have demanded no common perspicuity in an intelligent onlooker from some other sphere4 ,although the solar brake acted upon terrestrial rotation with no more than one-eleventh the power brought to bear upon that of ,venus1 it nevertheless sufficed during uncounted ages to hinder acceleration from reaching the pitch involving instability4 ,our embryonic planet had long ceased to be nebulous1 and had1 in fact1 shrunk by cooling nearly to its present dimensions before the die was cast4 ,then1 at last1 the hurrying effects of contraction prevailed over the slowing down due to tidal resistance1 axial speed overbore equilibrium1 and the spheroid divided4 ,now globes thus far advanced in condensation are apt to split less unequally than globes in a more primitive stage2 and the moon1 because late-born1 was of large size4 ,its mass is #a_/ha that of the earth2 the masses of ,titan and ,saturn are as #a to #d1fjj2 while ,jupiter's third and greatest satellite contains only #a_/aacjj part of the matter englobed in the parent-body4 ,moreover1 ,professor ,darwin has made it clear that the satellites of ,jupiter and ,saturn revolve now in orbits not widely remote from those at first pursued by them2 while the moon1 on the contrary1 started on its career almost1 if not quite1 from grazing contact with its primary4 ,owing to these two exceptional circumstances--its considerable relative mass and its close initial vicinity--the moon wielded over the earth tidal influence incomparably more powerful than that exerted by any of its compeers in the sun's realm4 ,the lunar-terrestrial system offers1 accordingly1 an example unique among those in solar subordination of a pair of globes1 the mechanical relations of which have been settled on their present basis by the predominating agency of bodily tides4 ,it holds forth1 too1 the one case in which origin by fission was possible4 ,professor ,darwin's communication to the ,royal ,society in #ahgi occasioned on this point a remarkable diversion of ideas4 ,saturn's rings were at last1 through the reasonings contained in it1 perceived to be illustrative of only one among many feasible modes of cosmic growth4 ,it became clear that a single cut-and-dried method would not answer all the infinitely varied purposes of creative design4 ,annulation might have served its turn1 but there were alternatives4 ,a fresh standpoint was virtually attained1 and the wide prospect commanded by it begins already to spread out invitingly before the gaze of investigators4 ,but whether the moon emerged from the earth as a protuberance1 or was abandoned by it as an irregular equatorial ring1 it was revolving1 when our theoretical acquaintance with it begins1 in a period of not less than two and not more than four hours1 quite close to the earth's surface2 while the nearly isochronous rotation of the earth was conducted with all but disruptive rapidity4 ,the situation is so suggestive that it needs only a short and tolerably safe leap in the dark to reach the conclusion that the two masses had very recently been one4 ,with their division1 at an epoch estimated to have been about sixty million years ago1 the process began by which the moon was pushed back along a widening spiral course to its present position1 the vanished rotational momentum of the earth cropping up again in the augmented orbital momentum of the moon4 ,and the transformation is1 at least in theory1 still going on4 ,tidal friction has further capabilities4 ,the transference of momentum from one part of a system to another is only the most obvious among the crowd of its results4 ,scarcely an element of movement escapes its influence4 ,it increases1 as a rule1 orbital eccentricity4 ,the smallest initial deviation from circularity develops1 through the inequality of accelerative action thence ensuing1 into pronounced ovalness4 ,that of the moon's path can in this way be accounted for4 ,moreover1 its plane was1 in all probability1 shifted simultaneously and under compulsion of the same power1 from its original coincidence with the earth's equatorial plane to the level it now occupies4 ,the obliquity of the ecliptic1 too1 is partially explicable on the same principle4 ',the present motion of the two bodies' 7to quote ,professor ,darwin's words71 are 'completely co-ordinated by the theory that tidal friction was the ruling power in their evolution4' ,holding this clue1 we are enabled to trace them back to the start of their dual existence1 and to follow the insensible modifications by which their state was moulded to its actual form4 ,in no other satellite-system is this possible4 ,no moon besides our own possesses a stock of orbital momentum large enough to intimate for it an analogous history4 ,planetary attendants elsewhere travel nearly in their original tracks2 the fluid ripples raised by them on the surfaces of their primaries lacked power to displace them sensibly4 ,their own rotation1 indeed1 seems to have been completely destroyed4 ,destroyed1 that is1 relatively to the destroying body4 ,there is a certainty that some1 there is the strongest likelihood that all1 of the ,jovian and ,saturnian satellites turn unchangingly the same face towards their primaries4 ,they rotate in the period of their several revolutions1 just as our moon does1 and as a consequence of the same cause4 ,tidal friction1 however1 appears to have been otherwise of subordinate importance in shaping their dynamical relations4 ,the agency will not1 then1 serve in all cases for a deus ex machin4 ,it is not indiscriminately efficacious4 ,the modes of its action have1 in each of the systems considered1 to be delicately distinguished4 ,the stage of development arrived at by the bodies affected1 their degree of viscosity1 their comparative mass and bulk1 their modes of motion1 all avail profoundly1 and it may be incalculably1 to modify the outcome4 ,the facility of error in estimates of the kind is illustrated by ,professor ,darwin's remark that the magnitude of the tide-raising force is only one factor of the product4#cb ,the other is relative movement4 ,now1 in the case of the moon the former continually augmented retrospectively1 while the latter fell off4 ,tidal generative power varies inversely as the cube of the distance2 in antique times1 then1 when the earth and moon revolved contiguously1 the bodily distortions they mutually produced were beyond question on an extremely large scale4 ,yet1 because of the near coincidence of the periods of the globes1 they must have been almost inoperative for frictional purposes4 ,the travelling of the piled-up matter over their surfaces was too slow to lend it much power as a friction-brake4 ,the insignificant waves raised by the sun were1 we are led to believe1 because of their swift relative motion1 more influential at that early epoch in checking terrestrial rotation than the colossal1 but nearly stationary waves due to the moon4 ,numerical calculations1 where they are practicable1 afford the only safe guide to this intricate field of inquiry4 ,it does not suffice to show that tidal action would have been of the kind required--would have taken the right direction--for bringing about some apparently anomalous result4 ,proof must1 besides1 be forthcoming that the action would have been of adequate power4 ,plausible guesses on the subject may be entirely fallacious4 ,the machine1 even if properly constructed for the end in view1 may work too feebly for its attainment4 ,we are1 for instance1 assured that no difficulty connected with the sense of planetary rotation need impede acceptance of the theory of planetary origin from separated rings1 since even if the embryo globes gyrated the wrong way at the outset1 solar tidal friction would promptly have reduced them to conformity with the general current of movement4 ,this is true in principle1 but will it bear quantitative investigation8 ,many promising hypotheses have broken down under the weight of figures2 whether this particular one is strong enough to survive their application remains to be seen4 ,we are1 indeed1 sure of its validity as regards ,mercury1 but the efficacy of tidal friction decreases as the sixth power of increasing distance1 and the actual rotation of ,venus furnishes an enigma sufficiently perplexing to discourage scrutiny of its dimly discerned antecedent conditions4 ,as regards the earth and the exterior planets1 the question could only be answered with the help of information which is not forthcoming4 ,the unexpected circumstance that the newly-discovered ninth ,saturnian moon circulates from east to west can thus be no more than tentatively explained by invoking this agency of change4 ,admitting 7as we seem bound to do7 that satellites are the offspring of the planets they attend1 there is no evading the conclusion that the small body under discussion was thrown off from a primary endowed with a rotation opposite to that now possessed by it4 ,and the reversal must have been completely brought to pass before the eighth satellite1 ,japetus1 came into existence4 ,the crux is most arduous2 there is no other resource for meeting it but to consider the effects on planetary rotation of solar tides1 and this ,professor ,w4 ,h4 ,pickering1 the discoverer of ,phbe1 has done4#cc ,but a cause may be true without being sufficient2 and close calculation will be needed to determine1 in this instance1 how the matter stands4 ,professor ,darwin's researches were fruitful just because they were definite4 ,they demonstrated1 once for all1 the diverse faculties of tidal friction as a cosmogonic agency1 and indicated clearly the departments of cosmogonic change in which its competence lay4 ,they availed1 moreover1 to determine for the earth-moon system the amount of work actually done by tidal friction in these several departments1 and to prove its large excess over the corresponding output in any other sub-system falling within the sphere of observation4 ,this memorable result suggests that our terrestrial home may be singular1 not only in its evolutionary history1 but in the innumerable adjustments fitting it to be the abode of life4 ,the relations of the earth and moon adumbrate1 and scarcely more than adumbrate1 the physical influences mutually exerted upon each other by numerous twin-globes in stellar space4 ,tidal friction is of maximum power in systems formed of equal masses2 and those of double stars are seldom widely disparate4 ,most1 if not all of them1 were1 besides1 primitively very near neighbours1 so that their symmetry must have been marred by conspicuous tidal deformations4 ,the results upon their development have been expounded in detail by ,dr4 ,see4 ,one of the most remarkable is the high average eccentricity of their orbits4 ,visual binaries1 with few exceptions1 travel in considerably elongated ellipses1 while spectroscopic binaries as a rule pursue approximately circular paths4 ,dr4 ,see's argument that the eccentricity of the more spacious systems was acquired under the influence of tidal friction1 during the long course of progressive separation1 is well-nigh irresistible4 ,true1 this line of explanation is not wholly clear of obstacles and incongruities4 ,yet they may probably be described as of a complicating1 rather than of a contradictory kind4 ,the theory of tidal friction is not a universal solvent of the difficulties encountered in the study of double stars4 ,that the mode of action it deals with had a contributory share towards regulating their mechanical arrangements may1 nevertheless1 be regarded as certain1 while the potency and perhaps even the manner of its operation varied extensively from system to system4 ,what precisely it effected in each lies beyond our range of determination4 ,for the data available regarding the viscosity1 density1 and axial movements of embryo star-pairs must always be too scanty and insecure to provide a basis for rigorous computations4 ,the mystery of the fore-time can never be entirely dissipated4 ,enough if we can look at it through a glass which darkens1 without distorting1 the objects presented in its field of view4 ,,footnotes3 ,footnote #bh3 ,smmtliche ,werke1 ,bd4 ,,vi41 pp4 #e-ab1 #ahci4 ,footnote #bi3 ,g4 ,h4 ,darwin1 ,encyclopdia ,britannica1 article on ',tides4' ,footnote #cj3 ,dynamik des ,himmels1 p4 #di4 ,footnote #ca3 ,darwin1 ,philosophical ,transactions1 vol4 clxxii41 p4 #ebh4 ,footnote #cb3 ,philosophical ,transactions1 vol4 clxxi41 p4 #hgf4 ,footnote #cc3 ,harvard ,annals1 vol4 liii41 p4 #eh4 ,,chapter ,,vi ,,the ,,fission ,,of ,,rotating ,,globes ,few people need to be told that a rotating fluid mass is shaped very much like an orange4 ,it assumes the form of a compressed sphere4 ,and the reason for its compression is obvious4 ,it is that the power of gravity1 being partially neutralized by the centrifugal tendency due to axial speed1 decreases progressively from the poles1 where that speed has a zero value1 to the equator1 where it attains a maximum4 ,here1 then1 the materials of the rotating body are virtually lighter than elsewhere1 and consequently retreat furthest from the centre4 ,the 'figure of equilibrium' thus constituted is a spheroid1 a body with two unequal axes4 ,in other words1 its meridional contour--that passing through the poles--is an ellipse1 while its equator is circular4 ,now we know familiarly1 not only that a spinning sphere becomes a spheroid1 but that the spheroid grows more oblate the faster it spins4 ,the flattened disc of ,jupiter1 for instance1 compared with the round face of ,mars1 at once suggests a disparity in the rate of gyration4 ,but there must be a limit to the advance of bulging1 or the spheroid1 accelerated ad infinitum1 would at last cease to exist in three dimensions4 ,clearly this unthinkable outcome must be anticipated2 at some given point the process of deformation must be interrupted4 ,a breach of continuity intervenes2 the train is shunted on to a branch line4 ,nor is it difficult to divine1 in a general way1 how this comes to pass4 ,equilibrium1 beyond doubt1 breaks down when rotation attains a certain critical velocity1 varying according to circumstances1 and the spheroid either alters fundamentally in shape or goes to pieces4 ,so much plain common-sense teaches1 yet the precise determination of the course of events is one of the most arduous tasks ever grappled with by mathematicians4 ,m4 ,poincar essayed it in #ahhe2cd it was independently undertaken a little later by ,professor ,darwin2#ce and the subject has now been prosecuted for eighteen years1 chiefly by these two eminent men1 with a highly interesting alternation of achievement1 one picking up the thread dropped by the other1 and each in turn penetrating somewhat further into the labyrinth4 ,the results1 nevertheless1 are still to some extent inconclusive2 they indicate1 rather than indite1 the genetic history of systems4 ,a strong light is1 indeed1 thrown upon it2 but in following its guidance1 the limitations of the inquiry have to be borne in mind4 ,the chief of these are1 first1 that the assumed spheroid is liquid2 secondly1 that it is homogeneous4 ,neither of these conditions1 however1 is really prevalent in nature1 so that inferences based upon them can only be accepted under reserve4 ,they were adopted1 not by choice1 but through the necessities of the case4 ,there was no possibility of dealing mathematically with bodies in any other than the liquid state4 ,the equilibrium of gaseous globes defies treatment1 except under arbitrary restrictions4#cf ,nor is it possible to cope with the intricacies of calculation introduced by variations of interior density4 ,cosmical masses1 as they actually exist1 are nevertheless strongly heterogeneous1 so that at the utmost only an approximation to the genuine course of their evolution can be arrived at by the most skilful analysis4 ,yet even an approximate solution of such a problem is of profound interest4 ,we can here only attempt briefly to specify its nature4 ,the course of change by which the equilibrium of a rotating liquid spheroid is finally overthrown has1 at any rate1 been satisfactorily tracked4 ,when its spinning quickens to a disruptive pitch1 it acquires three unequal axes instead of two4 ,the equator becomes elliptical like the meridians4 ,a ',jacobian ellipsoid' is constituted4 ,to this new form1 it would seem1 a long spell of stability must be attributed2 only its major axis becomes more and more protracted as cooling progresses1 and with cooling1 contraction1 and with contraction the increase of axial velocity4 ,then at last a crisis once more supervenes2 there is a collapse of equilibrium1 and its re-establishment involves the sacrifice of the last vestige of symmetry4 ,an 'apioid1' or pear-shaped body1 replaces the antecedent ellipsoid2 and its apparent incipient duality suggested to ,m4 ,poincar that the furrow unequally dividing it might deepen1 with still accelerated gyration1 into a cleft1 splitting the primitively single mass into a planet and satellite4 ,but this eventuality1 he was careful to note1 had no direct bearing on ,laplace's hypothesis1 which dealt with a nebula condensed towards the centre1 while the fissured apioid was liquid and homogeneous4#cg ,professor ,darwin followed out the conditions of this remarkable pear-shaped body to a closer degree of approximation than its original investigator had done1 and succeeded in virtually demonstrating its conditional stability4 ,but his analysis tended to smooth away the characteristic peculiarities of its shape1 and1 so far1 to diminish the probability of its ultimate disruption4 ,mr4 ,jeans1 on the other hand1 from an elaborate study of a series of cigar-shaped figures which in theory follow a parallel course of development to that pursued by ellipsoids1 derived1 by strict mathematical reasoning1 the actual separation of a satellite from one end of a parent-cylinder4 ,the representative figures reminded ,professor ,darwin 'of some such phenomenon as the protrusion of a filament of protoplasm from a mass of living matter4' ',in this almost life-like process' he saw 'a counterpart to at least one form of the birth of double stars1 planets1 and satellites4'#ch ,but the resemblance1 when examined dispassionately1 seems shadowy and evasive1 especially when we confront it with the case of double stars4 ,here1 indeed1 an entirely different set of conditions comes into play from that postulated by ,poincar and ,darwin1 since stars are certainly not liquid bodies4#ci ,they are most likely gaseous to the core1 though the indefinite diffusiveness incident to gaseity is restricted by their condensed photospheric surfaces4 ,this circumstance intimates the possibility that the results arrived at for liquid globes by mathematical analysis may1 with qualifications1 be extended to stars2 but the necessary qualifications1 unfortunately1 are vague and large2 for too little is known regarding the physical condition of stellar spheres to warrant assumptions that might provide a secure basis for research4 ,the evolution of binary stars can then only be treated of inferentially1 not rigorously2 and we must1 at the outset1 discard the idea that it is illustrated by the phenomena of double nebul4 ,many such objects thought to supply clinching visual arguments for the actual effectiveness of slow cosmic fission proved1 on the application to them of the late ,professor ,keeler's searching photographic methods1 to be knots on spiral formations4 ,their mutual relations are then entirely different from what had been supposed by telescopic observers2 they are1 in fact1 still structurally connected1 and the mode of their origin1 however inviting to conjecture1 scarcely comes within the scope of definitely conducted inquiries4 ,their future destiny is no more accessible to it than their past history1 and only by a daring flight of imagination can we see in spiral nebul the prototypes of double stars4 ,questions as to the mode of genesis of these latter systems have1 in recent years1 acquired extraordinary interest4 ,conclusive answers cannot1 indeed1 at present be given to them1 because the terms in which they are couched lack distinctness1 owing to our lack of knowledge2 but probable answers may legitimately supply their place1 at least ad interim1 above all when their probability is heightened almost to certainty by the accumulation of circumstantial evidence4 ,observations and investigations of stellar eclipses have created a new department of astrophysics1 and have vastly widened the domain of cosmogony4 ,they have brought to notice a number of systems1 not merely in a primitive1 but seemingly in an inchoate stage of development4 ,the periods of occulting stars are nearly all of them less than seven days1 although one extending to thirty-one has lately been recognised2 and the comparative length of the intervals of obscuration shows them to be produced by the circulation in narrow orbits of distended globes4 ,these are characteristic symptoms of juvenility1 for1 as we have seen1 orbits widen and periods lengthen with the efflux of time through the frictional power of bodily tides4 ,now the class of stars which obviously and certainly undergo eclipses has some outlying members of a still dubious nature4 ,and their marginal position serves greatly to enhance the present1 the prospective1 and the retrospective interest attaching to them4 ,these remarkable objects vary in light continuously4 ,their phases are not1 like those of ,algol1 mere interruptions to a regular course of steady shining4 ,they progress without a moment's sensible pause2 they are represented graphically by a smoothly-flowing1 symmetrical curve4 ,the eclipses by which they are occasioned--if they are so occasioned--must1 accordingly1 succeed each other in a strictly unbroken series4 ,no sooner has one terminated than the next commences4 ,one star passes first behind1 then in front of its companion1 and their combined brightness is seen undimmed only during the few moments of actual maximum4 ,this means that they revolve in contact2 they are separated by no sensible gap of space4 ,goodricke's variable1 ,lyr1 is held to be thus constituted4 ,the possibility1 at least1 of employing the 'satellite-theory' to account for its changes was demonstrated some years ago by ,mr4 ,g4 ,w4 ,myers1 of ,indiana4#dj ,he found the system to be composed of two barely separated ellipsoids1 circulating in the visual plane1 and producing1 by their successive transits1 two unequal eclipses in the course of each period of #abia days4 ,the joint mass of the pair is just thirty times that of our sun1 but their mean density has the almost incredibly small value of #a_/abjj that of water4 ,their real existence is conditional upon the possibility that masses much more tenuous than atmospheric air should radiate with the intensity of true suns4 ,spectroscopic observations are not wholly unfavourable to ,mr4 ,myers's hypothesis1 but their interpretation is hampered by discrepancies so numerous and perplexing that no secure inference can be derived from them4 ,moreover1 the star supposed to be alone presented to view at the principal minimum is that giving the bright-line spectrum2 yet it is compulsorily assumed1 in order to meet the exigencies of the situation1 to be much more massive1 while much less intrinsically bright1 than its companion4 ,this is disquieting1 but nearly everything connected with ,lyr is more or less disquieting4 ,a variable of the same type1 but much fainter1 was made the subject of a similar inquiry by ,mr4 ,myers in #ahih4da ,u ,pegasi never attains ninth magnitude2 hence1 spectroscopic complications equally with spectroscopic verification remain at present out of sight4 ,the star1 nevertheless1 excites keen interest1 and claims sustained attention4 ,its light-curve has been laid down with exquisite accuracy at ,harvard ,college1 and shows two slightly unequal minima to be comprised within a period of nine hours1 signifying1 on the adopted theory1 the occurrence of alternating eclipses at intervals of four and a half hours4 ,the distance from centre to centre of the occulting stars1 the smaller of which is of about eight-tenths the brightness of the larger1 'does not materially differ1' ,mr4 ,myers tells us1 'from the sum of their radii1 suggesting the probable existence of the apioidal form of ,poincar4' ,if they do not actually coalesce1 the component bodies revolve in contact1 and rotate synchronously4 ,thus1 it is hard to say whether ,u ,pegasi should be accounted as a single pear-shaped mass spinning in the time of light-change1 or as a close couple circulating freely in that identical period4 ,the mean density of the system appears to lie between one-third and one-fourth that of the sun4 ,another specimen of the 'dumb-bell' system is possibly met with in ,r#b ,centauri4 ,the narrow range of its variation makes it a delicate object to observe2 but ,mr4 ,a4 ,w4 ,roberts1 who first noticed its peculiarity in #ahif1 has since accumulated an extensive series of wonderfully accurate visual determinations of its fluctuating brightness1 and has besides rendered them the basis of an able and exhaustive theoretical discussion4#db ,the double period of ,r#b ,centauri is restricted to fourteen hours thirty-two minutes4 ,within this brief span quadruple phases are included--that is to say1 two evenly balanced maxima and two slightly disparate minima4 ,these result1 ,mr4 ,roberts concludes1 from the mutual eclipses of interpenetrating ellipsoids1 one somewhat more luminous than the other1 revolving--if they can properly be said to revolve--in an orbit inclined #cb to the visual plane4 ,they are of just one-third the solar density1 and the forms satisfying photometric requirements by the varying areas of luminous surface presented to sight in different sections of their path show a surprising agreement with the bi-prolate figure given by ,professor ,darwin's analysis as the shape of a body on the verge of disruption through accelerated rotatory movement4 ,the inference is1 then1 almost irresistible that ,r#b ,centauri really exemplifies the nascent stage of binary stars4 ,to establish this completely1 however1 spectroscopic data are needed2 and they are difficult to procure for a star below the seventh magnitude4 ,no such obstacle impedes the investigation of the analogous1 but much brighter object1 ,v ,puppis4 ,detected as a spectroscopic binary by ,professor ,pickering in #ahie1 this star traverses so wide an orbit in the short period of thirty-five hours as to imply--if the published details are correct--that the pair possess no less than #cdh times the gravitational power of the sun4 ,they are1 nevertheless1 according to ,mr4 ,roberts1 fifty times more tenuous1 and each globe should have a diameter of about #af-a_/b million miles2 yet nothing of all this is incredible4 ,the light-curve of ,v ,puppis1 as traced by ,mr4 ,roberts1 is closely modelled upon that of ,u ,pegasi4 ,and he postulates similar conditions of eclipse4 ,it rests with the spectroscope to determine whether those conditions are realized or not4 ,probably all short-period variables are binaries1 with coincident orbital- and light-cycles4 ,but all are not occulting binaries4 ,there are some--we are still ignorant of their proportionate numbers--which undergo a course of light-change1 apparently compatible with an occulting hypothesis1 yet certainly escape eclipse4 ,professor ,campbell has made it unmistakably clear that ,geminorum is thus constituted4#dc ,two stars are present1 but their plane of motion is inclined at an unknown angle to the line of sight2 it does not approximate to coincidence with it4 ,now the possibility is not excluded that ,v ,puppis belongs to the same class4 ,mr4 ,roberts's assumptions are1 indeed1 in themselves plausible1 and they may at any moment be proved1 by a few well-timed spectrograms1 to be undeniably true4 ,the one conclusive test of their truth is the cessation of radial movement at epochs of minimum4 ,evidently1 if the diminution in lustre be due to an eclipse1 the eclipsing and eclipsed bodies must be crossing the line of sight just when the obscuration is deepest4 ,there is no evading this geometrical requirement1 and it must be rigorously complied with in the circular orbits traversed by bodies revolving in contact4 ,before1 then1 ,mr4 ,roberts's theory of ,v ,puppis can be accepted with implicit confidence1 it has to be ascertained whether a zero of radial speed is reached concurrently with the photometric minima4 ,if so1 these may be unhesitatingly set down as eclipse-phenomena2 if1 on the contrary1 the decline in brightness prove to be unrelated to a slackening of speed1 then the supposition that it accompanies and indicates a transit must be peremptorily discarded4 ,moreover1 the spectroscopic verdict as regards ,v ,puppis can safely be applied to stars with similar light-curves1 especially to ,r#b ,centauri and ,u ,pegasi1 and may serve to clear away some of the intricacies connected with the exceptional system of ,lyr4 ,the measurement of a single spectrographic plate might thus1 by deciding the test-case of the binary in the poop of ,argo1 be made essentially to supply the lack of desirable1 but at present unattainable determinations as regards a considerable number of analogous objects4 ,the existence of stellar systems of the 'dumb-bell' type would violate no mechanical law4 ',roche's limit' does not apply to globes comparable in size4 ,the range of disparity within which it holds good has not1 indeed1 been theoretically established2 but it may be said1 in general terms1 to concern the relations of planets and satellites 7to use a purposely vague phrase71 not those of double stars4 ,what the law asserts is that a subordinate small body cannot revolve intact at a less distance than #bdd radii of its primary from that primary's centre1 if their mean density be the same4 ,for satellites of slighter consistence the limit should be extended4 ,our own moon1 for instance1 could never have circulated1 without being rent in pieces by tidal strains1 in an orbit less than #bb1jjj miles in diameter4#dd ,bodies of co-ordinate mass are1 however1 exempted from the prohibitive rule against mutual approach4 ,no analytical veto is imposed upon the origin by fission of double stars1 or upon the subsistence of stellar ,siamese twins4 ,the inequalities of their mutual attractions avail to distort1 not to disrupt1 such embryo globes4 ,their individuality1 therefore1 once created1 is in a manner indestructible4 ,it tends1 in fact1 to become more pronounced as the orbital span gradually widens through the reactive effects of tidal friction4 ,the 'dumb-bell' condition may then be regarded as in a manner transitory4 ,nor can we be assured of its actuality otherwise than by the peculiar nature of the eclipses attending upon it1 taken in connection with correlated spectroscopic observations proving eclipses of the kind veritably to take place4 ,the disclosure1 by such means1 of systems so strangely conditioned promises to afford a deeper insight than would else have been possible into the cosmical order1 and fills a blank page in the marvellous history of sidereal birth and growth4 ,,footnotes3 ,footnote #cd3 ,acta ,mathematica1 vol4 vii41 ,stockholm1 #ahhe4 ,footnote #ce3 ,proceedings ,royal ,society1 vols4 xlii41 lxxi42 ,philosophical ,transactions1 vols4 cxcviii41 cxcix41 ,series ,a4 ,footnote #cf3 ,j4 ,h4 ,jeans1 ,philosophical ,transactions1 vol4 cxcix41 ,series ,a1 p4 #a4 ,footnote #cg3 ,figures d'quilibre d'une ,masse ,fluide1 p4 #agb4 ,footnote #ch3 ,proceedings ,royal ,society1 vol4 lxxi41 p4 #ahc4 ,footnote #ci3 ,j4 ,h4 ,jeans1 ,astrophysical ,journ41 vol4 xxii41 p4 #ic4 ,footnote #dj3 ,astrophysical ,journal1 vol4 vii41 p4 #a4 ,footnote #da3 ,astrophysical ,journal1 vol4 viii41 p4 #afc4 ,footnote #db3 ,monthly ,notices1 vol4 lxiii41 p4 #fbg4 ,footnote #dc3 ,astrophysical ,journal1 vol4 xiii41 p4 #ij2 ,science1 ,july #bg1 #aijj4 ,footnote #dd3 ,g4 ,h4 ,darwin1 ,the ,tides1 p4 #cbg4 ,,chapter ,,vii ,,world ,,building ,,out ,,of ,,meteorites ,the idea is seductive that we see in every meteoric fire-streak a remnant of the process by which our world1 and other worlds like or unlike it1 were formed4 ,it is not a new idea4 ,chladni entertained it in #agid2 and it has since from time to time been revived and rehabilitated with the aid of improved theoretical knowledge and a larger array of facts4 ,survivals are tempting to thought4 ,it costs less effort to realize differences in degree than differences of kind4 ,the enhanced activity of familiar operations is readily imagined1 while perplexity is apt to shroud the results of modes of working strange to experience4 ,hence the presumption in favour of continuity2 nor can it be said1 even apart from our own mental inadequacy1 that the presumption is other than legitimate4 ,nature is chary of her plans1 lavish of her materials4 ,her aims are characterized by a majestic unity1 but she takes little account 7that we can see7 of surplusage or wreckage4 ,now1 it seems likely that meteorites represent one or the other of these two forms of waste stuff4 ,they are analogous1 apparently1 either to the chips from shaped blocks1 or to the dust and rubbish of their destruction4 ,let us consider what it is that we really know about them4 ,it cannot be said that the sources of our information are scanty4 ,fully one hundred millions are daily appropriated by the earth as she peacefully spins through the ether4 ,their absorption leaves her unaffected4 ,it produces no perceptible change in her internal economy1 and makes no sensible addition to her mass4 ,the hundred millions of small bodies taken up have1 nevertheless1 in ,professor ,langley's opinion1 an aggregate weight of more than one hundred tons4#de ,and this increment is always going on4 ,yet its accumulated effect is evanescent by comparison with the enormous mass of our globe4 ,that it was more considerable in past ages than it is at present might be plausibly conjectured1 but cannot reasonably be maintained4 ,geological deposits contain--unless by some rare exception--no recognisable meteoric ingredients4 ,there is nothing to show that the earth was subject to a heavier bombardment from space during the ,silurian era than in the twentieth century4 ,nor could the whole of its constituents have been1 in any case1 thus provided4 ,out of kiln-dried fragments1 like the ,mazapil iron or the 'thunder-stones' of ,adare1 a terraqueous planet could not have been formed4 ,this objection1 urged by ,mr4 ,o4 ,fisher1#df is seemingly irrefutable4 ,meteorites signify their existence to us1 in general1 only by the bale-fires of their ruin2 but in a few cases their tangible relics come to hand4 ,those substantial enough to escape total disintegration through atmospheric resistance to their swift movements plunge into the sea or bury themselves in the earth1 and in a certain proportion of cases find their way to museums and laboratories1 where they are subjected to the searching investigation demanded by their exotic origin4 ,its results are scarcely what might have been expected4 ,aerolites--as these samples from space are distinctively called--are not chemically peculiar2 they consist exclusively of the same elementary substances composing the crust of the earth2 but their mineralogy is strongly characteristic4 ,they are extremely complex structures1 formed apparently in the absence of water1 and with a short supply of oxygen2 the further condition of powerful pressure is indicated with some probability1 nay1 with virtual certainty for those including small diamonds1#dg while prolonged vicissitudes of fracture and re-agglomeration are possibly recorded by the brecciated texture of many of these rocky trouvailles4 ,their aspect is thus anything but primitive2 each fragment tacitly lays claim to an eventful history2 they suggest a cataclysm1 of which we behold in them the shattered outcome4 ,the nature of such cataclysms is scarcely open to conjecture2 only a hint regarding it may be gathered from the circumstance that the most profound terrestrial formations are those which approximate most closely to the mineralogical peculiarities of meteorites4 ,nevertheless1 the only ascertained relationships of meteorites are with comets4 ,in every system of shooting stars the primary body most probably is1 or at any rate was1 a comet4 ,each appears to be the offspring of a cometary parent1 and develops pari passu with its decay4 ,the view has hence been adopted1 and not without justification1 that comets in their primitive integrity are simply 'meteor-swarms4' ,assent may be given to it with some qualifications which we need not here stop to discuss4 ,what immediately concerns us is the interesting question as to the constitution of meteor-swarms4 ,what is the real meaning of the term8 ,what does it convey to our minds8 ,a meteor-swarm may be defined as a rudely globular aggregation of small cosmical masses1 revolving under the influence of their mutual attraction1 round their common centre of gravity4 ,each must revolve on its own account1 though all have the same period2 and their orbits may be inclined at all possible angles to a given plane1 and may be traversed indifferently in either direction4 ,from this tumultuous mode of circulation collisions should frequently ensue1 but they would be of a mild character4 ,they could not be otherwise in a system of insignificant mass and correspondingly sluggish motion4 ,we are considering1 it must be remembered1 only cometary swarms1 as being the only collections of the sort that come1 even remotely1 within our ken2 and comets include the minimum of matter4 ,this we are entitled to infer from the fact that none of those hitherto observed1 whether conspicuous or obscure1 newly arrived from space1 or obviously effete1 have occasioned the slightest gravitational disturbance to any member of our system4 ,a cometary swarm1 if left to itself1 might eventually shape itself into a reduced model of the ',saturn' planetary nebula4 ,colliding particles should1 owing to their loss of velocity1 subside towards the centre1 and accrete into a globular mass4 ,a predominant current of movement would1 through their elimination1 gain more and more completely the upper hand2 and it would finally1 with the inevitable diminution of energy1#dh be restricted almost wholly to the principal plane of a system1 composed essentially of a rotating nucleus encompassed by a wide zone of independently circulating meteorites4 ,but this mode of evolution is not even distantly followed by comets4 ,it would be possible only if they were isolated in space1 and1 in point of fact1 their revolutions round the sun are of overwhelming importance to their destinies4 ,the sun's repulsive energy causes them to waste and diffuse with expansion of splendid plumage4 ,under the sun's unequal attraction at close quarters they are subject to disruption1 and the upshot of the tidal stresses acting upon them is the dispersal of their constituent particles along the wide ambit of their oval tracks4 ,we are1 nevertheless1 invited to look further afield4 ,cometary meteor-swarms may be only miniature specimens of the contents of space4 ,why should not remote sidereal regions be thronged with similar assemblages1 colossal in their proportions1 countless in number8 ,and may they not supply the long-sought desideratum of a suitable 'world-stuff' for the construction of suns and planets8 ,from some such initial considerations as these ,sir ,norman ,lockyer developed1 in #ahhg1 a universal meteoritic hypothesis1 designed on the widest possible lines1 based on promising evidence1 and professing to supply a key to the baffling enigma of cosmical growth and diversification4 ,the meteoric affinities of comets formed its starting-point2 comets were assimilated to nebul2 and from nebul were derived1 by gradual processes of change1 all the species of suns accessible to observation4 ,the view was of far-reaching import and magnificent generality1 but its value avowedly rested on a body of facts of a special kind4 ,in this it differed from the crowd of ambitious speculations regarding the origin of things by which it had been preceded4 ,in this it attained an immeasurable superiority over them1 if only the testimony appealed to could be established as valid4 ,indeed1 it is scarcely too much to say that1 whether it were valid or not1 the mere circumstance of having called the spectroscope as a witness in the high court of cosmogony constituted an innovation both meritorious and significant4 ,the spectrum of the nebul was a standing puzzle4 ,a theory which set out by making its meaning plain secured at once a privileged position4 ,this was seemingly accomplished by ,sir ,norman ,lockyer through the means of some simple laboratory experiments on the spectra of meteorites4 ,certain 'low temperature' lines of magnesium given out by the vapours of stony aerolitic fragments were shown to fall suspiciously close to the chief nebular lines previously classed as 'unknown4' ,the coincidences1 it is true1 were determined with low dispersion1 and were published for what they were worth1 but they looked hopeful4 ,their substantiation1 had it been feasible1 would have marked the beginning of a new stadium of progress4 ,nature1 however1 proved recalcitrant4 ,the suggested agreements avowed themselves1 on closer inquiry1 as approximate only2 magnesium light makes no part of the nebular glow1 and nebulium1 its main source1 evades terrestrial recognition4 ,the light of cosmic clouds is sui generis--it includes no metallic emissions2 while the fundamental constituents of meteorites are metals variously assorted and combined4 ,the decipherment of the nebular hieroglyphics was the crucial test2 its failure to meet it left the hypothesis seriously discredited2 for coincidences between spectral rays1 common to nearly all the heavenly bodies1 naturally counted for nothing4 ,yet the investigation had its uses4 ,the energy with which it was prosecuted1 the ingenuity and resource with which it was directed1 told for progress4 ,there has been a clash of arms and a reorganization of forces4 ,thought was stirred1 observation and experiment received a strong stimulus1 fresh affluents to the great stream of science began to be navigated4 ,efforts to prove what had been asserted were fruitful in some directions1 and the work of refutation had inestimable value in defining what was admissible1 and establishing unmistakable landmarks in astrophysics4 ,the discussion1 it must be admitted1 threw very little light on the part played by meteorites in cosmogony4 ,their world-building function remains largely speculative4 ,doubts of many kinds qualify its possibility1 and lend it a fantastic air of unreality4 ,but this may in part be due to a defect of imaginative power with which the universe was not concerned4 ,waiving1 then1 preliminary objections1 we find ourselves confronted with the fundamental question3 ,given a meteor-swarm of the requisite mass and dimensions1 is there any chance of its condensing into a planetary system8 ,sir ,norman ,lockyer set aside this branch of his subject4 ,his hypothesis was1 in fact1 'pre-nebular4' ,he assumed that the small solid bodies with which it started would1 in course of time1 become completely volatilized by the heat of their mutual impacts1 and that the resulting gaseous mass would thenceforward comport itself after the fashion imagined by ,laplace4 ,professor ,darwin regarded the matter otherwise4 ,it seemed to him possible to combine the postulates of the meteoric and nebular theories in a system planned on an original principle4 ,for this purpose it was necessary to excogitate a means of rendering the kinetic theory of gases available for a meteor-swarm4 ',the very essence1' he wrote1#di 'of the nebular hypothesis is the conception of fluid pressure1 since without it the idea of a figure of equilibrium becomes inapplicable4' ,m4 ,faye abandoned this idea2 he built up his planets out of incoherent materials1 thereby avoiding the incongruities1 but forfeiting the logical precision of ,laplace's stricter procedure4 ,professor ,darwin consented to forfeit nothing2 he stood forward as a syncretist1 his object being to 'point out that by a certain interpretation of the meteoric theory we may obtain a reconciliation of these two orders of ideas1 and may hold that the origin of stellar and planetary systems is meteoric1 whilst retaining the conception of fluid pressure4' ,for the compassing of this end he adopted a bold expedient4 ,fluid pressure in a gas is 'the average result of the impacts of molecules4' ,fluid pressure in a meteor-swarm might1 he conceived1 be the net product of innumerable collisions between bodies to be regarded as molecules on an enormously magnified scale4 ,the supposition is1 indeed1 as ,kepler said of the distances of the fixed stars1 'a big pill to swallow4' ,between molecules and meteorites lies a wide unbridged gap4 ,the machinery of gaseous impacts is obscure4 ,it can be set in motion only by ascribing to the particles concerned properties of a most enigmatical character4 ,these particles are1 however1 unthinkably minute2 and in sub-sensible regions of research the responsibilities of reason somehow become relaxed4 ,we are far more critical as to the behaviour of gross1 palpable matter1 because experience can there be consulted1 and is not unlikely to interpose its veto4 ,meteorites are1 doubtless1 totally dissimilar from molecules1 however many million-fold enlarged2 and they would infallibly be shattered by collisions which only serve to elicit from molecules their distinctive vibrations4 ,moreover1 the advance of the shattering process would admittedly end the prevalence of fluid pressure4 ,so that the desired condition1 even if initially attained1 would be transitory4 ,there is1 besides1 a radical difference between a group of bodies in orbital circulation and a congeries of particles moving at haphazard1 unconstrained by any predominant law of force4 ,a meteoric swarm belongs to the first category2 it is a community swayed in some degree by a central power2 while the gaseous contents of a retort or a balloon obey purely individual impulses4 ,the analogy looked for by ,professor ,darwin can then scarcely be said to exist1 and his paper stands out as a monument of ingenious mathematical treatment applied to an ideal state of things4 ,an aggregation of revolving meteorites has no figure of equilibrium1 and it is through the consequences necessarily resulting from this property that mathematicians are enabled to trace the progressive changes of a rotating fluid mass4 ,in the absence of any such direct means of attack1 their position regarding the problem presented by an assemblage of flying stones is not much better than that occupied by ,kant1 face to face with an evolving universe4 ,it seems1 nevertheless1 clear that a meteor-swarm can be impelled to condense no otherwise than through the effects of collisions among its constituents4 ,when the irregularities of movement upon which their occurrence depends are got rid of1 the system must remain in statu quo4 ,order makes for permanence2 a tumultuary condition is transient4 ,the eventual state of the system can1 however1 be no more than partially foreseen4 ,bodies arrested in their flight should fall inward1 hence a central mass would form and grow2 but the production of planets would seem to be conditional upon the existence of primitive inequalities of density in the swarm4 ,these might serve as nuclei of attraction for meteoric infalls1 not yet completely exhausted1 but plying with harmless fire one at least of the globes they helped to shape4 ,there could1 indeed1 on this showing1 have been no such harmonious succession of events as constituted the predominant charm of ,laplace's scheme4 ,the planets should be supposed to have issued pell-mell out of a chaos2 or1 rather1 the chaos should have contained from the beginning the seeds of a predestined cosmos4 ,its evolution would have been like that of the oak from the acorn1 an unfolding of what was already essentially there4 ,and it may be that at this stage of penetration into the past1 the unaided human intellect meets its ne plus ultra4 ,there is a vital heart of things which we cannot hope to reach4 ,thought instinctively pauses before the vision of the symbolical brooding dove4 ,to resume4 ,meteoric cosmogony has a rational basis4 ,the modes of action it demands are still operative4 ,enfeebled almost to evanescence compared with the vigour they must have needed to be efficacious in world-building1 they continue to make play in our nocturnal skies4 ,they make play1 it is true1 with a very small quantity of material2 but it may even now be distributed elsewhere in relatively enormous profusion1 and in the solar system itself it presumably was much more abundant formerly than it now is4 ,the earth has been raking up meteoric granules by hundreds of millions daily during untold ages1 and her zone of space is still very far from being swept clean4 ,the persistence of the supply1 however1 may be occasioned by the continual arrival of reinforcements from interstellar realms4 ,comets appertain to1 and travel with1 the sun's cortge1 and this is also inevitably true of comet-born meteors4 ,but a multitude besides circulate independently of comets1 and with much higher velocities4 ,their orbits are1 then1 hyperbolic2 they belong to the category of 'irrevocable travellers1' and by their capture we are privileged to possess genuine shreds of sidereal matter4 ,universal space contains probably a vast stock of them1 yet there is nothing to prove their collection into swarms4 ,the spectroscope supplies no assurance to that effect2 it has given its verdict against the meteoric constitution of nebul and temporary stars4 ,and if we admit1 through the persuasion of mineralogical testimony1 that the aerolites so strangely landed on terrestrial soil are really the dbris of ruined worlds1 we can see for them no chance of restoration4 ,solitary they are1 even if they occasionally pursue one another along an identical track1 and solitary they must remain4 ,bodies do not of themselves initiate mutual circulation4 ,planetary or stellar outcasts cannot become re-associated into a gravitational system4 ,of a cosmic swarm1 as of a poet1 it may be said1 ,nascitur1 non fit2 and their birth-secret is undivulged4 ,,footnotes3 ,footnote #de3 ,the ,new ,astronomy1 p4 #aig4 ,footnote #df3 ,american ,journal of ,science1 vol4 xi41 p4 #dba1 ,june1 #aija4 ,footnote #dg3 ,carbon does not liquefy under ordinary conditions4 ,in the production of his artificial diamonds ,m4 ,moissan employed tremendous pressure and great heat2 and1 although the genuineness of his products has been denied 7,combes1 ,moniteur ,scientifique1 ,november1 #aijc71 his methods at least seem to have approximated to those by which ,nature fabricates her most authentic crystals4 ,footnote #dh3 ,sir ,r4 ,ball1 ,the ,earth's ,beginnings1 p4 #bdc4 ,footnote #di3 ,proceedings of the ,royal ,society1 vol4 xlv41 p4 #d4 ,,chapter ,,viii ,,cosmogony ,,in ,,the ,,twentieth ,,century ,prospective and retrospective inquiries into physical conditions stand very much on the same footing4 ,the same degree of uncertainty attaches to results of both kinds2 the same qualifications need to be applied to them2 a similar reserve is understood to accompany our admission of them4 ,the reserve grows more marked as science unfolds to our surprised apprehension the multiplex possibilities of ,nature4 ,the time has gone by when 'men of light and leading' could draw cheques for unlimited amounts on the bank of public credulity4 ,not that the balance has diminished1 but that it is reserved for other uses4 ,most of us in these days1 have learnt to 'look before and after' for ourselves1 and we instinctively mix the proverbial grain of salt with what is told to us1 even on the highest authority4 ,ideas are on the move2 dim vistas are opening out2 much that lies beyond the verge of actual experience is seen to be possible1 and sedate reasoning may at any moment suffer outrage by fantastic discovery4 ,hence1 finality of assertion is out of date4 ,the secular parallax affecting men's views of the universe is nowhere more strongly apparent than in the trend taken by speculations as to its origin4 ,they have become more subtle1 more far-reaching1 yet less confident4 ,they have ramified in unexpected directions1 but rather tentatively1 than with the full assurance of attaining absolute truth4 ,laplace considered only the solar system1 from which he arbitrarily excluded comets4 ,on the vast sidereal world he bestowed barely casual attention4 ,sir ,william ,herschel1 on the other hand1 occupied himself exclusively with the growth-processes of nebul1 relegating the details of planetary evolution to a position of secondary importance4 ,later1 the spectroscope having become available for discriminating generic differences among the suns in space1 their relative ages1 the order of their succession1 their mutual affinities1 claimed predominant attention4 ,just now1 however1 the flood of speculation is too high to be restrained within separate channels2 cosmogonists look far afield2 they aim at obtaining a general survey of relations bewildering in their complexity4 ,to some extent they have succeeded2 parts are beginning to find their places in a great whole2 links are seen to connect phenomena at first sight seemingly isolated2 on all sides analogies are springing into view4 ,the unwearied circling of the moon and its imperturbable face remind us how a sun may have been born2 the flash of every meteor suggests the mode by which suns die4 ,the filmy traceries of comets intimate the nature of the force acting in nebul2 the great cosmic law of spirality is remotely hinted at by the antipodal disturbances of the sun4 ,thus1 one set of facts dovetails into the next2 none can be properly considered apart from the rest4 ,the limitations of the human mind impose1 nevertheless1 restrictions of treatment4 ,individual efforts cannot grapple with the whole of the known and the knowable1 and the larger part of both is included in the scope of modern cosmogony4 ,it deals with all that the skies hold1 visibly or invisibly2 draws unstintingly on time past and time to come2 concerns itself equally with gradual transformations and sudden catastrophes1 with the dissipation and concentration of energy1 with the subtle interplay of matter and force1 with physical and ultra-physical1 chemical and electrical modes of action4 ,but let us consider a little more particularly how things actually stand1 so as to collect some definite ideas regarding the lines of advance practicable and promising for the immediate future4 ,to begin with our domestic circle4 ,the insecure state to which ,laplace's scheme has been reduced by the assaults of numerous objectors has found compensation in the development of the tidal theory4 ,much light has thereby been thrown upon planetary pre-history4 ,the relations of planets to the sun1 and of satellites to planets1 have been rendered comparatively intelligible4 ,noticeable above all is the discovery thence ensuing of the earth's suggestive position1 just outside the boundary of the region where planetary rotation was destroyed by sun-raised tides1 and with it the prospects of planetary vitality4 ,moreover1 the dubious state of the inchoate terrestrial spheroid1 consequent upon its intermediate situation1 accounts for the peculiar mode of birth of the moon1 and the distinctively binary character of the earth-moon system2 while the variety perceptible in the circumstances of the different planets precludes the employment of any single recipe for their development from a primal vortex4 ,the forces concerned1 we can now see1 acted in a far more complex manner than could formerly have been supposed1 and their balance was proportionately more delicate4 ,to which side it would have inclined in a given case must then often be incalculable1 or calculable only with the guidance of the known result4 ,the strict bonds of reasoning have thus become somewhat relaxed1 and difficulties that looked formidable have1 in the long run1 proved not to be insuperable4 ,but conviction has also grown faint4 ,the old1 imposing faade of theory remains erect2 the building behind it has been1 for the most part1 pulled to pieces1 and the architect has yet to be found who can reconstruct it to our satisfaction4 ,on one point we have1 nevertheless1 acquired certainty4 ,it is now known that comets with their dependent trains of meteors are aboriginal in the solar system4 ,they are no unlicensed intruders1 but collateral relations of the planetary family4 ,possibly they represent waste scraps of world-stuff which escaped the action of the formative machinery2 and if so1 they exemplify its primitive texture4 ,not that their composition need be1 on this supposition1 identical with that of the planets4 ,a sifting of elements would have been likely to accompany the processes of cooling and contraction4 ,comets were1 perhaps1 made 7to speak illustratively7 of the white of the nebulous egg1 planets of its yolk4 ,but in any case we may safely regard the glimmering fabrics of acetylene and cyanogen that occasionally illuminate our skies as shearings from a wide-spreading1 fleecy haze1 flung aside before 'the starry tides' had as yet begun to 'set towards the centre4' ,in one respect the quality of these relics is a surprise4 ,they show no chemical affinity with nebul4 ,their spectra are radically different from nebular spectra1 gaseous or continuous4 ,they accordingly lend no countenance1 although not fatally adverse to the view that the sun was once1 in the distinctive sense1 a nebulous star4 ,the grand topic of sidereal succession is no longer abandoned to fruitless surmises4 ,broad lines have been laid down1 along which1 so far as we can at present see1 progress must inevitably have been conducted4 ,and one fact of overwhelming significance in this connection is entirely of recent discovery4 ,the multitudinous existence of obscure bodies in space had1 indeed1 been foreseen as a logical necessity long before ,bessel founded the ',astronomy of the ,invisible'2 but its strong substantiation is almost wholly due to the use of modern spectrographic methods4 ,decrepit or dusky suns are assuredly no imaginary product1 but a potent reality1 though it would be too much to assert that all have sunk to extinction by the same road4 ,nor is it absolutely certain that their present state is uniformly the outcome of prolonged decay4 ,circumstances connected with many of them suggest rather a congenital incapacity for shining4 ,we stand1 too1 on firmer ground than our predecessors in respect to the history of stellar systems4 ,that its course is mainly prescribed by the influence of tidal friction has been ably demonstrated by ,dr4 ,see4 ,telescopic double stars can be led back by the aid of this clue to an initial stage1 when they revolved close together1 very much like the earth and moon in ,professor ,darwin's theory2 and it was owing to their voluminousness and the unequal attractions it engendered that their orbits became enlarged and elongated to the degree generally observed4 ,this theoretical inference has been confirmed with singular aptness by the discovery of spectroscopic binaries4 ,pairs circling in orbits too narrow for visual discernment are the natural complement of pairs just divisible with the telescope2 the first class represent the unseen1 early stages of the second4 ,the two together form an unbroken sequence of stellar systems1 for spectroscopic binaries include couples fully separated1 and still separating1 as well as others barely divided1 and revolving almost in contact4 ,nay1 they include specimens1 we are led to believe1 of globes conjoined into the apioidal figure theoretically investigated by ,darwin and ,poincar1 which may be regarded as preparatory to the development by fission of two mutually revolving stars from one primitive rotating mass4 ,some of these supposed dumb-bell systems are variable in light2 and if the eclipse-rationale of their obscurations be confirmed by the spectroscope1 there is no gainsaying the inference that each flickering object is composed of two stars actually contiguous1 if not confluent4 ,now1 compound stars are by no means of exceptional occurrence4 ,their relative abundance has been found to augment rapidly with every advance in our knowledge of the heavens4 ,from the measures of stellar radial velocity lately carried out at the ,yerkes ,observatory by ,professors ,frost and ,adams1 it appears that the proportion of binary to single stars considerably exceeds ,professor ,campbell's earlier estimate4 ,if those giving helium-spectra are alone considered1 there are most probably as many of one kind as of the other4 ,but why the distinction8 it may be asked4 ,the answer is not far to seek4 ,helium stars are the most primitive1 and form the closest and most readily apparent systems4 ,the companions of more fully developed stars would be likely to give less striking spectroscopic signs of their presence4 ,a physically double star must always remain such4 ,there is no law of divorce by which it can put away its companion1 although their relations must alter with time4 ,but their alteration tends continually to enhance the difficulty of their detection4 ,for as the members of a pair are pushed asunder by tidal friction their velocity slackens1 and the tell-tale swing of their spectral lines diminishes in amplitude1 and finally1 by its minuteness1 evades observation4 ,and since the majority of spectroscopic satellite-stars are very imperfectly luminous1 their eventual telescopic discovery1 when far enough away from their primaries to be optically separable from them1 would rarely ensue4 ,it must then be concluded that half the stars in the heavens 7let us say7 broke up into two or more bodies as they condensed4 ,what follows8 ,well1 this4 ,half the stars in the heavens were1 from the first1 incapacitated from becoming the centres of planetary systems4 ,to our apprehension1 at least1 it appears obvious that a binary condition must have inhibited the operations of planetary growth4 ,these innumerable systems are doubtless organized on a totally different principle from that regulating the family of the sun4 ,the nebular hypothesis1 even in its most improved form1 has no application to them2 the meteoritic hypothesis still less4 ,mathematical theories of fluid equilibrium1 combined with a long series of changes due to tidal friction1 afford some degree of insight into the mode of their origin and the course of their development4 ,yet the analogy with the earth-moon couple1 which irresistibly suggests itself1 is imperfect1 and may be misleading1 owing to the wide difference in state between plastic globes approaching solidification1 and sunlike bodies radiating intensely and probably gaseous to the core4#ej ,the world of nebul confronts us with entire cycles of evolutionary problems1 which can no longer be treated in the offhand manner perforce adopted by ,herschel4 ,the objects in question are of bewildering variety2 yet we can trace1 amid their fantastic irregularities1 the underlying uniformity of one constructive thought4 ,nearly all show1 more or less markedly1 a spiral conformation1 and a spiral conformation intimates the action of known or discoverable laws4 ,their investigation must1 indeed1 be slow and toilsome2 its progress may long be impeded by the interposition of novel questions1 both in physics and mechanics2 nevertheless1 the lines prescribed for it seem definite enough to give hope of its leading finally to a clear issue4 ,and when at last something has been fairly well ascertained regarding the past and future of nebulous spirals1 no contemptible inroad will have been made on the stupendous enigma of sidereal relationships4 ,its aspect1 if we venture to look at it in its entirety1 is vast and formidable4 ,not now1 as in former times1 with a mere fragment of creation--a single star and its puny client-globes1 one of which happens to be the temporary abode of the human race--but with the undivided1 abysmal cosmos1 the science of origin and destiny concerns itself4 ,the obscure and immeasurable uncertainties of galactic history invite or compel attention4 ,we know just enough to whet our desire to know a great deal more4 ,the distribution of stars and nebul is easily seen to be the outcome of design4 ,by what means1 we cannot but ask ourselves1 was the design executed8 ,how were things ordered when those means began to be employed8 ,how will they be ordered when all is done8 ,for an ultimate condition has1 presumably1 not yet been reached4 ,and if not1 agencies must be at work for the perfecting of the supreme purpose1 which are not1 perhaps1 too subtle for our apprehension4 ,meanwhile1 facts bearing on sidereal construction are being diligently collected and sifted1 and we shall do well to suspend speculation until their larger import is made known4 ,the inquisitions of science do not cease here4 ,they strive to penetrate a deeper mystery than that of the scattering in space of stars and nebul4 ,what are they made of8 is the further question that presents itself4 ,what is the nature of the primal world-stuff8 ,whence did it obtain heat8 ,by what means was motion imparted to it8 ,if it be urged that such-like topics elude the grasp of finite intelligence and belong to the secrets of creative power1 we may reply that we are not entitled1 nor are we able1 to draw an arbitrary line1 not to be transgressed by our vagrant thoughts4 ,the world has been1 by express decree1 thrown wide to their excursions1 and it is not for us to restrict their freedom4 ,we need not fear getting too near the heart of the mystery2 there is no terminus in the unknown to which we can travel by express2 in a sense1 we are always starting1 and never get nearer to our destination4 ,but that is because it retreats before us4 ,we do1 in truth1 advance2 and as we advance the mists clear1 and we see glimpses beyond of imperishable order1 of impenetrable splendour4 ,our inquiries need not then be abandoned in despair at the far-reaching character they have spontaneously assumed4 ,from the earliest times there has been a tendency to regard varieties of matter as derivative4 ,they have been supposed to be procured by supramundane agency1 or by the operation of inherent law1 from some universal undifferentiated substance4 ,we moderns call that substance 'protyle1'#ea and believe ourselves to be in experimental touch with it4 ,the implications of this view we shall consider in the next chapter4 ,,footnotes3 ,footnote #ej3 ,cf4 ,jeans1 ,astrophysical ,journal1 vol4 xxii41 p4 #ic4 ,footnote #ea3 ,a term signifying 'first matter1' constructed from corresponding ,greek words by ,roger ,bacon1 and revived by ,sir ,william ,crookes4 ,,chapter ,,ix ,,protyle3 ,,what ,,is ,,it8 ,the notion of a primordial form of matter meets us at every stage of cosmogonical speculation4 ,it is the outcome of an instinctive persuasion that1 if we could only 'lift the painted veil' of phenomena1 the real business of the universe would be found to be proceeding in the background1 'without haste or rest1' on a settled plan everywhere the same2 that uniformity is fundamental1 diversity only incidental2 and that the transformations of the one simplified substance might be represented by a single formula1 the discovery of which would place in our hands the master-key to the locked secrets of the universe4 ,among untutored thinkers some familiar kind of matter1 idealized and generalized1 commonly stood for the typical world-stuff4 ,water was the first favourite4 ,thales1 the 'wise man' of ,miletus1 procured his cosmos by precipitation from an aqueous solution1 and many savage tribes have devised analogous expedients4 ,anaximenes regarded air as the universal solvent2 ,heracleitus replaced it with fire1 and set on foot a scheme of what is now often designated 'elemental evolution4' ,from the perpetual 'flux of things' he conceived that the four substances selected by ,empedocles as the bases of nature were not exempt1 and a fragment of his scheme survived in ,francis ,bacon's admission of the mutual convertibility of air and water4 ,in the main1 however1 the author of the ',novum ,organum' adhered to the ,paracelsian doctrine of an elemental triad1#eb although he regarded the association of salt as a fundamental 'principle' with sulphur and mercury as inept and unnecessary4#ec ,these twilight fancies faded in the growing light of chemical science2 yet the mental need that they had temporarily appeased survived1 and had somehow to be satisfied4 ,an ',ur-,stoff' was still in demand1 but the nineteenth century characteristically attempted to supply it by weight and measure4 ,dalton's combining equivalents afforded the warrant for ,prout's hydrogen hypothesis4 ,the problem to be faced was to find a unit-atom by the varied combinations of which all the rest of the chemical atoms might be formed4 ,the condition indispensable to be fulfilled was that their weights should be exact multiples of that of the unit1 and it came near to fulfilment by the hydrogen-atom or semi-atom4 ,it was1 nevertheless1 a case in which approximate agreement was of no avail2 the adverse decision of the balance finally became unmistakable2 and ,prout discreetly fell back1 in #ahca1ed upon the expedient of deriving hydrogen itself from some body lower in the scale4 ,his hypothesis1 in short1 dissolved into a conjecture4 ,it had only emphasized the stipulation that the 'protyle' of the ancients must be such as would serve not only for the physical unification of the sum of things1 but likewise as the substratum of all the chemical species4 ,meanwhile1 the theoretical search for it had been carried on in widely different fields of inquiry4 ,laplace's speculations1 no less than ,herschel's observations1 had led to the conception of some kind of 'fire-mist' as the genuine star-plasm4 ,but its nature and properties remained indefinite1 or were assigned at the arbitrary choice of adventurous cosmogonists4 ,so the 'shining fluid' of space was 'everything by turns and nothing long1' until ,sir ,william ,huggins1 in #ahfd1 gave it spectroscopic individuality4 ,the 'recognition-mark' of nebulium is a vivid green ray1 by the emission of which it is known to have a concrete existence4 ,yet the little that has besides been learned about it discountenances its identification with the materia informis of antique philosophy4 ,this we should expect to be the subtlest of all substances4 ,professor ,campbell1 however1 has gathered indications that nebulium is denser than hydrogen4 ,its luminosity1 at least1 which is invariably associated with that of hydrogen1 spreads less widely in the same formations2 it is confined to a lower level4 ,the nebulium-atom is not1 then1 the chemical or the cosmical unit4 ,this evasive entity1 or something that curiously simulates it1 has proved to be of less recondite origin4 ,sir ,william ,crookes is amply justified in claiming the venerable designation of protyle for the 'radiant matter' first produced in his vacuum-tubes nearly thirty years ago4 ,the discovery was astonishing and unsought1 and its significance has not yet been measured4 ,matter assumes the 'fourth state1' in which it is neither solid1 liquid1 nor gaseous1#ee under the compulsion of an electric discharge in high vacua4 ,at an exhaustion of about one-millionth of an atmosphere the manner of its transit abruptly alters4 ,conduction gives way to convection4 ,luminous effects are abolished4 ,the tubes cease to glow with brilliant1 parti-coloured stri2 the poles are no longer marked by shimmering halos or brushes2 only a green phosphorescence is seen where the glass walls of the receptacle are struck by the stream of projected particles4 ,they come1 with half the velocity of light1 exclusively from the negative pole1 the positive pole remaining inert4 ,hence the name 'cathode-rays1' bestowed by ,goldstein on the carriers of electricity in highly-exhausted bulbs4 ,these mysterious1 sub-sensible agents possess certain very definite properties4 ,their paths are deflected in a magnetic field2 they can traverse metallic films2 and their investigation in the open1 thereby rendered feasible1 has shown them to possess photographic efficacy1 and the faculty of breaking down electrical insulation2 moreover1 they transport a negative charge of fixed amount1 and have a determinate momentum4 ,they are1 then1 assuredly no mere pulsations of the ether2 unless our senses 'both fail and deceive us1' their quality is material4 ,material1 yet not quite with the ordinary connotation of the term4 ,the most essential circumstance about the cathode-rays is that they remain unmodified by the chemical diversities of the originating gases4#ef ,a hydrogen tube yields identically the same radiant matter as an oxygen or a nitrogen tube4 ,here1 then1 at last we have within our grasp undifferentiated substance--matter not yet specialized1 neither molecular nor atomic1 matter destitute of affinities1 exempt from the laws of combination--matter in its inchoate1 and perhaps ultimate form2 in a word1 the far-sought protyle4 ,already1 in #ahgi1 ,sir ,william ,crookes conjectured the infinitesimal missiles propelled from the cathode to be the 'foundation-stones of which atoms are composed4'#eg ,and in #ahhf he pronounced them more decisively to be the raw material of atoms1 which1 to ,sir ,john ,herschel's apprehension1 bore the unmistakable stamp of a 'manufactured article4' ,nor did his recent commentator refrain from attempting distantly to divine the method of their construction1 or from laying his finger on the by-products and residues associated with it1#eh although he felt compelled to relegate the cosmic factory to the edge of the world1 where inconceivable things may happen4 ,all this1 indeed1 seemed1 in the late ,victorian era1 like mounting the horse of ,astolfo for a trip to the moon2 and sane common-sense pronounced it fantastic enough to 'make ,democritus weep and ,heracleitus laugh4'#ei ,but we have since learned from ,nature herself some tolerance of audacities4 ,step by step the new order of ideas has irresistibly come to the front4 ,it owed its origin to ,sir ,william ,crookes's skill in producing high vacua1 and the consequent development in his tubes of radiant effects4 ,then1 in #ahgi1 universal importance was claimed for them1 and matter in the 'fourth state1' by a revival of the dreams of the ancients1 expanded into a kind of visionary protyle4 ,philipp ,lenard made the next advance towards its actualization by slipping it1 in #ahid1 through an aluminium window1 and watching its behaviour towards ordinary matter4 ,two years later ,rntgen rays made their entry on the scene2 and before the end of #ahif ,becquerel1 hurrying along the track of novelties1 came upon the momentous discovery of radio-activity4 ,a revision of ideas has ensued4 ,some time-honoured assumptions have had to be discarded2 so-called laws have been found to need qualification2 the old system of physics is consequently out of gear1 and much time and patient labour must be expended upon the adjustment of the new and improved system destined to replace it4 ,the leading and indisputable fact of the actual situation is that a number of hitherto unsuspected modes of energy have been disclosed as widely operative in nature4 ,all are of a 'radiant' character4 ,they travel in straight lines with enormous speed2 they start from a material base1 and produce their several effects on reaching a material goal4 ,now1 these effects are closely alike1 notwithstanding that the rays themselves are radically dissimilar4 ,those of the cathodic kind are corpuscular4 ,they consist of streaming particles1 each1 according to ,professor ,j4 ,j4 ,thomson1 of about one-thousandth the mass of the hydrogen atom4 ,others1 the noted 'alpha rays1' are atomic2 they are supposed to aggregate into helium4 ,finally1 the ,rntgen variety are ethereal2 they are composed of light-vibrations reduced in scale1 and augmented correspondingly in frequency4 ,what is most remarkable is that these various forms of activity give rise1 by different means1 to very much the same results4 ,they are1 in fact1 distinguishable only by careful observation4 ,they possess in common1 though not to the same degree1 the faculties of penetrating opaque matter1 of impressing sensitive plates1 of evoking fluorescence2 while under the impact of cathode and ,rntgen rays1 as well as of ultra-violet light1 insulated electric charges leak away and evanesce4 ,there is1 however1 one clear note of separation between cathodic and ,x rays in the sensibility of the former1 and the indifference of the latter1 to magnetic influence4 ,thus alone1 it would appear1 is electrified matter set apart from what we call ether4 ,a magnet acts only upon bodies carrying an electric charge2 so that1 if flying corpuscles could be obtained in a neutral condition1 the only tangible distinction between the various kinds of rays would vanish4 ,but this is evidently impracticable4 ,indeed1 advanced physicists abolish the material substratum of the corpuscle1 and assign its attributes to the associated atom of electricity4 ,it is1 at any rate1 undeniable that the electrical relations of matter become more intimate as our analysis of its constitution goes deeper4 ,ether1 electricity1 matter1 all seem to merge together in the limit2 their differences ultimately evade definition4 ,so animal and vegetable life appear to coalesce in their incipient stages1 and strike apart with advance towards a higher perfection4 ,the various branches of inorganic nature1 too1 possibly spring from a common stock4 ,our powers of discrimination fail to separate them as we trace them downward2 but that may be because of the inadequacy of the guiding principles at our command4 ,a larger synthesis is demanded for the harmonizing of multitudinous facts1 at present grouped incongruously1 or left in baffling isolation2 and it is rendered increasingly difficult of attainment by the continual growth of specialization4 ,year by year details accumulate1 and the strain of keeping them under mental command becomes heavier2 yet what can be known must1 in its essentials1 be known as a preliminary to extending the reign of recognised law in ,nature4 ,sooner or later1 nevertheless1 the wealth of novel experience recently acquired will doubtless be turned to the fullest account4 ,just now1 we can grasp only tentatively its far-reaching import4 ,that it bears profoundly on the hoary problem of the genesis of visible things is sufficiently obvious4 ,the questions of what matter is1 and of how it came to be1 have been cleared of some of the metaphysical cobwebs involving them ab antiquo1 and insistently crave definite treatment by exact methods4 ,we should1 indeed1 vainly aspire to reach--or to comprehend1 even if we could reach--an absolute beginning4 ,to quote ,clerk ,maxwell's words3 ',science1'#fj he wrote1 'is incompetent to reason upon the creation of matter itself out of nothing4 ,we have reached the utmost limit of our thinking faculties when we have admitted that1 because matter cannot be eternal and self-existent1 it must have been created4' ,the discovery that atoms disintegrate into corpuscles does not1 then1 bring us any nearer to the heart of the mystery2 but it is eminently suggestive as regards secondary processes4 ,acquaintance with ultra-atomic matter1 begun within the narrow precincts of ',crookes's tubes1' has advanced rapidly since 'radiology' took its place among the sciences4 ,for1 from the time when ,becquerel first saw a plate darkened by the photogenic projectiles of uranium1 and ,madame ,curie sifted radium from the refuse of the mines of ,joachimsthal1 the lines of proof steadily converged towards the conclusion that chemical atoms are not only divisible1 but that their decay progresses spontaneously1 irresistibly1 in fire1 air1 earth1 and water1 as part of the regular economy of ,nature4 ,to explain further4 ,radio-active bodies are composed--according to ,rutherford's plausible hypothesis--of atoms in unstable equilibrium4 ,the gradual changes incidental to their own internal activities suffice to bring about their disruption4 ,and their explosive character is obviously connected with unwieldy size1 since uranium1 thorium1 and radium1 the three substances pre-eminent for radio-activity1 possess the highest atomic weights known to chemistry4 ,the precarious balance1 then1 of each of these complex1 though infinitesimally small systems is successively overthrown1 regardless of external conditions or environment1 their constituent parts being hurled abroad with the evolution of an almost incredible amount of energy4 ,their products include cathode-rays2 matter in the 'fourth state1' matter a thousand times finer than hydrogen1 is ejected in torrents from the self-pulverized atoms of radium4 ,moreover1 the issuing rays are equivalent to currents of negative electricity4 ,each corpuscle bears with it an electron1 or is itself an electron1 for the choice between the alternatives is open4 ,in either case1 we are confronted with matter apparently in its ultimate form2 and to that form ordinary1 substantial bodies tend to become reduced4 ,electrons may fairly be called ubiquitous4 ,they occur in flames1 near all very hot masses1 wherever ultra-violet light impinges on a metallic surface2#fa they are freely generated by ,rntgen and cathode-rays2 they are the agents of electrical transmission in conductors4 ,everywhere throughout the universe1 atoms are thus in course of degradation into corpuscles4 ,but no information is at hand as to the scene or mode of their reconstitution4 ,the waste and decay are patent2 the processes of compensation remain buried in obscurity4 ,indeed1 ,sir ,william ,crookes anticipates the complete submergence1 at some indefinitely remote epoch1 of material substance in protyle1 the 'formless mist' of chaos4 ,he assumes an identity between the past state and the future1 leaving1 however1 the present unexplained4 ,the break-up of matter1 in fact1 does not render its construction the more intelligible4 ,running-down is an operation of a different order from winding-up4 ,it is an expenditure of a reserve of force4 ,it needs no effort2 it accomplishes itself4 ,but to create the reserve for expenditure demands foresight and deliberate exertion2 it implies a designed application of power4 ,now each atom is a storehouse of energy1 representing the force primitively applied to reduce some thousands of free electrons to the bondage of a harmoniously working system4 ,its disruption is accompanied by the dissipation of the energy previously accumulated in it2 and that atomic systems are not calculated for indefinite endurance is one of the most surprising of modern discoveries4 ,the secret of their original construction is1 none the less1 impenetrable4 ,that they are composed of protyle--that their clustering members are corpuscles moving under strong mechanical control--is more than probable4 ,and the law of order adumbrated by what are called the 'periodic' relations of the chemical elements shows that their concourse was very far from being fortuitous4 ,but beyond this point there is no holding-ground for distinct thought4 ,we are ignorant1 too1 whether the process of building matter out of protyle is at present going on1 or was completed once for all in the abysmal fore-time1 decay being now definitive4 ,nor is it likely that we shall ever succeed in capturing with recognition a brand-new atom freshly minted for cosmical circulation4 ,,footnotes3 ,footnote #eb3 ,first introduced by ,basilius ,valentinus4 ,see ,fowler's edition of the ,novum ,organum1 p4 #egf1 note4 ,footnote #ec3 ,thus recurring1 as ,mr4 ,fowler remarked 7loc4 cit471 to ,geber's earlier view4 ,footnote #ed3 ,dictionary of ,national ,biography1 vol4 xlvi41 p4 #dbf4 ,footnote #ee3 ,crookes1 ,philosophical ,transactions1 vol4 clxx41 p4 #afc4 ,footnote #ef3 ,j4 ,j4 ,thomson1 ,the ,discharge of ,electricity through ,gases1 p4 #aie2 ,philosophical ,magazine1 vol4 xliv41 p4 #caa4 ,footnote #eg3 ,science1 ,june #bf1 #aijc4 ,footnote #eh3 ,proceedings of the ,chemical ,society1 ,march #b1 #ahhh4 ,footnote #ei3 ,times1 ,march #cj1 #ahhh4 ,footnote #fj3 ,encyclopdia ,britannica1 article ',atom4' ,footnote #fa3 ,fleming1 ,proceedings ,royal ,institution1 vol4 xvii41 p4 #afi4 ,,chapter ,x ,,universal ,,forces ,we find it equally impossible to conceive of matter without force1 as of force without matter4 ,the two modes of action1 or of being1 are inseparable4 ,yet our minds strongly distinguish between them2 they impart a dual aspect to the world4 ,phenomena are not simple manifestations of disembodied energy1 if such a thing could be2 they have a substantial basis which1 nevertheless1 eludes apprehension1 and seems to slip away into nothingness if we try to empty it of its immaterial contents4 ,nor do these energize in the void4 ,they and the bodies they animate are knowable only in combination1 and exist1 to our apprehension1 only on the condition of mutual dependence4 ,all we can do towards discriminating them is to fix our attention predominantly on one or the other side of things1 and so facilitate thought by drawing ideal lines of demarcation4 ,just as there are many forms of matter--all springing1 we are led to believe1 from an undifferentiated1 fundamental world-stuff--so there are various kinds of force1 reducible1 possibly without exception1 to one universal principle4 ,their correlation1 indeed1 has been already in large measure demonstrated2 heat1 light1 electricity1 and kinetic power are known to be equivalent and interchangeable2 but there are outstanding activities1 which resist assimilation1 and seem to originate under different conditions from the rest4 ,forces manifest themselves chiefly through attractive and repulsive effects1 varying in accordance with their natures and the modification of attendant circumstances4 ,the minute particles of matter1 for instance1 cohere2 they cling together tenaciously2 yet no pressure avails to bring them into actual contact2 at a certain point of mutual approach1 they develop an invincible power of resistance to any further encroachments upon their separate molecular domains4 ,and it is this faculty which gives to matter its distinctive property of hardness4 ,it is rendered tangible to sense just by its recalcitrance to constraint4 ,neither the mode of operation nor the nature of the forces by which molecules are organized into masses is known2 while the power acting on the masses thus organized1 and regulating by its action the mechanism of the universe1 is fully as baffling to comprehension4 ,wonder at its results is blunted by familiarity2 presented to us as novelties1 they should be pronounced to outrage reason4 ,the relations of gravity are of the utmost simplicity2 and they are1 on that very account1 supremely perplexing4 ,they are governed by one steadfast law1 the same everywhere1 and under all varieties of conditions within the range of experiment or precise observation4 ,it governs impartially every kind and quality of matter1 taking no notice of its states or combinations1 ignoring its subjection to chemical1 thermal1 magnetic1 or electrical influences4 ,gravity is not only indifferent1 but inevitable and inexorable2 there is no resisting its sway2 no screen serves as a shelter against its persuasions2 it spreads equably in all directions1 becoming enfeebled1 like wave-motion1 in the strict proportion of its diffusion from a centre over successive spherical surfaces4 ,its most singular peculiarity1 however1 is its apparent unconcern with time4 ,the gravitational pull is virtually instantaneous2 its transmission--if it be transmitted--takes place millions of times faster than that of light2 the finest tests have1 so far1 failed to elicit symptoms of delay4 ,these would be found in minute discrepancies between calculated and observed perturbational effects in the heavens4 ,the action of gravity1 if propagated with finite velocity1 should differ for bodies preserving an invariable distance from its source1 and for bodies travelling towards or away from it4 ,their movement would modify the law of attraction4#fb ,yet1 up to the present1 it has proved impossible to detect the slightest deviation from the plain rule of inverse squares4 ,again1 the penetrative faculty of this strange force seems absolute and unlimited4 ,we know by ordinary experience that we cannot diminish the weight of an object by interposing any kind of shield between it and the earth2 and no refinement in experimentation avails to alter this result4 ,that it is so1 is a fortunate circumstance for the harmony of the world4 ,we can dimly imagine the riot of confusion that would ensue if a transiting globe could intercept the attraction1 as it does the light1 of a central governing mass4 ,but from the wonderfully adjusted universal order gravitational eclipses are excluded2 nor does the densest body throw even the faintest gravitational shadow4 ,the nature of a power so singularly conditioned is almost inconceivable2 yet attempts have not been wanting to fathom the mystery that surrounds it4 ,professor ,osborne ,reynolds1 in the ,rede ,lecture for #aijb1 claimed to have arrived at 'a complete1 quantitative1 purely mechanical explanation of the cause of gravitation1' based on the 'dilatancy' of a granular medium in close piling4 ,but his working model of the universe will probably be remembered only as a lesson in the 'inversion of ideas1' showing that with skill and ingenuity a fairly concordant outcome of phenomena may be derived from antagonistic hypotheses4 ,in this author's view matter is equivalent to a deficiency of mass1 the spaces where his cosmic grains are relatively few1 because their arrangement is out of gear1 being driven towards one another by the pressure of the surrounding medium1 in which they are compactly stowed1 and therefore numerous4 ,thus1 the acting forces in nature are made to depend upon the compression by the denser medium of interspatial tracts of rarer consistence1 forming what we call matter4 ,the theory is difficult1 if not impossible of acceptance1 not because it involves the overthrow of conceptions which may be rooted in habitual modes of thought1 rather than in absolute truth1 but because of its startling postulates and large vacuities4 ,to be valid1 it should be complete2 and there are obvious chasms in the vast expanse of ground which it covers with surprising1 though only partial success4 ,the multa renascentur of the poet is verified by the revolutions no less of thought than of speech4 ,flights of minute material particles have served the turn of theorists often1 and in more ways than one1 and have as frequently been consigned to discredited oblivion2 but they are in vogue once more4 ,george ,louis ,lesage1 of ,geneva1 devoted sixty-three of the seventy-nine years of his life1 which came to an end in #ahjc1 to the elaboration of a mechanical rationale of gravity1 first given to the world in the ,transactions of the ,berlin ,academy of ,sciences for #aghb1 and with details of amplification in his ,trait de ,physique ,mcanique1 edited by ,pierre ,prvost in #ahah4fc ,the explanation it offered of molar attractions was by the supposed unceasing impacts of 'ultramundane corpuscles1' speeding in countless numbers and at fabulous velocities1 from nowhere everywhere1 and thus enforcing the mutual approach of masses of gross matter4 ,this involved the supposition of an infinitesimal screening effect1 producing a small inequality in the strength of the bombardment on the sheltered and unsheltered sides of the bodies exposed to it4 ,this inequality1 in fact1 was taken to be the causa causans of gravity4 ,yet its production encountered a difficulty4 ,there was required for it a trifling degree of opacity in every kind of matter1 while perfect gravitational transparency is asserted by the most delicate observations4 ,lesage1 then1 reduced the arrests laid upon his particles to a minimum2 one in ten thousand1 for instance1 might at the utmost be intercepted by the terrestrial globe4#fd ,even this insignificant minority1 however1 would suffice1 through the surrender of their momentum to the impeding bodies1 to endow them with the noted property of gravitation4 ,clerk ,maxwell urged the objection that the accompanying loss of kinetic energy by the corpuscles should1 if transformed into heat1 render all gravitating bodies white-hot4 ,but ,professor ,j4 ,j4 ,thomson holds that the transferred corpuscular energy might1 instead of reappearing in thermal form1 be converted into some highly penetrative species of radiation capable of escaping unperceived into surrounding space4#fe ',a simple calculation1' he adds1 'will show that the amount of kinetic energy transformed per second in each gramme of the gravitating body must be enormously greater than that given out in the same time by one gramme of radium4' ,this consequence of ,lesage's theory takes one's breath away2 the 'fables of the ,talmud' seem1 by comparison1 easy of belief2 nevertheless1 ,lord ,kelvin#ff declared it in #ahgc to be more complete in the expository sense1 and not more arduous in its assumptions1 than the kinetic theory of gases4 ,its fundamental postulate1 at any rate1 has been curiously verified in the course of recent researches into the arcana of physics4 ,entities in some degree corresponding to the ultramundane corpuscles of the ,genevese philosopher do actually exist4 ,electrons are being continually expelled from bodies in all parts of the universe2 they issue forth under all conceivable conditions and in unlimited numbers4 ,space is perhaps thronged with them2 no material object can be exempt from their multitudinous buffetings1 which are beginning to be taken account of in many cosmical speculations1 and cannot certainly be ignored in efforts to solve the most obvious to superficial apprehension1 the most intricate on a profound consideration1 of all cosmical problems4 ,but there is one fatal objection to an electronic theory of gravitation4 ,the agency appealed to travels too slowly to be available for the required purpose4 ,the velocity of light1 there is reason to believe1 sets a limit impossible to be surpassed or even attained by the velocity of electrons2 yet it is incomparably smaller than the rate of gravitational transmission4 ,tisserand estimated at six million times the quickness of luminous travel the minimum speed at which the sun's attraction must be propagated in view of the imperceptibility in planetary observations of effects corresponding to a time-inequality2#fg and this value may be taken as authentic4 ,so colossal a discrepancy excludes any kind of impact-rationale of the mutual pull of heavy masses2 ,lesage's corpuscles remain 'ultramundane'2 their identification with known atoms or sub-atoms appears to be precluded2 no products of ionic disintegration possess the qualities necessarily to be ascribed to them4 ,we turn1 then1 inevitably to the menstruum of mysteries1 the bank of the insolvent in speculation1 to the all-serviceable ether4 ,ethereal radiations exercise an impulsive power2 light-pressure has secured a recognised status among cosmic agencies2 and every vibrational system of the luminous type undoubtedly shares the faculty by which light tends to drive minute particles forward along the lines of its propagation4 ,professor ,j4 ,j4 ,thomson1 accordingly1 considered that but for the drawback of their insufficient velocity1 'very penetrating ,rntgen rays' might with advantage be substituted for corpuscular streams as the cause of gravity4#fh ,they would1 in some slight degree1 be absorbed by encountered masses1 to which they would impart a proportionate amount of momentum4 ,two bodies mutually shadowing one another would1 under such circumstances1 be drawn together with a force varying as the inverse square of distance2 and if further they absorbed the impinging rays strictly in the measure of their density 7as observation shows to be approximately the case71 the attraction would increase in the same ratio as the product of their masses4 ,but ,rntgen rays travel with the precise velocity of light2 they are1 in truth1 ultra-invisible light2 and they must hence be regarded as hopelessly incompetent to explain an influence transmitted at least six million times more rapidly4 ,this was fully admitted by ,dr4 ,h4 ,a4 ,lorentz1#fi who1 five years ago1 weighed the vibrational hypothesis of gravity in the balance of rigorous calculation1 and found it wanting4 ,his equations yielded the unexpected result that1 if its postulates were granted1 the noted attractions between massive bodies could subsist only on the terms of an incessant waste of electro-magnetic energy4 ,but this is of course inadmissible4 ,the theory involving such a consequence stands self-condemned1 to say nothing of the wholly inadequate rate of propagation afforded by it4 ,impulsion hypotheses1 whether by corpuscles or rays1 being hopelessly discredited1 ,dr4 ,lorentz reverted to a half-forgotten speculation by ,mosotti1 which1 though sixty years old1 struck him as capable of being adapted to modern requirements4 ,it was of an electrical nature1 and1 in the novel shape given to it1 supposed gravitational action to depend upon strains of the ether due to the disturbing effects of the positive and negative ions constituting ordinary matter4 ,these 'states' of the medium are distinct in kind2 they cannot neutralize one another2 and the familiar law of attraction represents their resultant effect4 ,to bring it about much has to be taken for granted2 yet the hypothesis can lay claim to one singular prerogative4 ,although the disturbances invoked by it traverse the ether with no more than the standard speed of light1 it appears from ,dr4 ,lorentz's investigation that1 owing to certain modifications in the properties of the medium produced by moving matter1 the planetary perturbations betraying loss of time in gravitational transmission would1 on the electrical theory1 be so small as to evade detection4 ,as regards this crucial point1 the ,dutch physicist has hit upon a felicity of explanation entirely original1 and1 as it were1 unsought4 ,an 'undulatory theory' of gravity1 adumbrated1 rather than advanced by ,mr4 ,whittaker in #aijb1gj excited hopes that the ideal aim of science--a complete unification of the forces of ,nature--might at last be within reach4 ,based upon a striking mathematical research1 it exhibited the attraction between masses as1 in a manner1 the integration of innumerable wave disturbances1 propagated at a rate not strictly definable1 but perhaps immensely surpassing that of gravity4 ,no suggestion was made as to the primary mode or cause of agitation1 yet it seemed much to learn that the medium we are cognizant of in space might be capable of transmitting the pull of gravity4 ,unfortunately1 however1 the physical foundation of this reassuring congruity proves to be weak or unsound4 ,the mathematical mill works magnificently1 but the grist put into it is of dubious quality4 ,stripping ,mr4 ,whittaker's result of its purely analytical form1 ,dr4 ,johnstone ,stoney showed that an assumption of extreme improbability lay concealed in his equations1 which could not1 he concluded1 be seriously taken to correspond with the reality of things4#ga ,there would then seem to be no alternative but to accept ad interim the electro-dynamical view of the nature of gravity4 ,if not true1 it is at least not obviously false4 ,through its subtlety it escapes direct confutation4 ,and the method of exclusions1 by eliminating competitors1 has left it in virtual possession of the field4 ,nothing is more curious in the history of recent science than the continual and irresistible growth which it records in the importance of electrical phenomena4 ,all others tend to become merged in them2 the most varied data of experience claim to be translated into electrical terminology4 ,they are not1 assuredly1 rendered more intelligible by the process1 but it at any rate abolishes the confusion incidental to multitudinous points of view4 ,thus1 in the last resort1 we find electrical forces 7if they may be so designated7 swaying the world4 ,what they essentially consist in1 we cannot tell2 the utmost that may reasonably be hoped for is to arrive at a clear conception of modes of action reduced to antagonistic stresses1 by which the play and counterplay of the universe may be kept up4 ,and to this extent we find it possible to understand how electricity works the ethereal machinery4 ,it is strongly dualistic4 ,the nearer we get to the foundations of nature1 the more sharply positive and negative charges appear to be differentiated4 ,the opinion is nevertheless held by some inquirers that negative electricity is the only substantive kind1 and that its complement is ordinary matter deprived of some of its negative particles4 ,this1 in fact1 revives ,franklin's 'one fluid theory1' only with the substitution of negative for positive electricity as the active principle4#gb ,but we are met by the doubt whether 'ordinary matter' can be said to exist in and by itself4 ,if it do1 the mode of its existence becomes more and more baffling to comprehension1 as the association of mass with charge makes its way into the foreground of thought4#gc ,moreover1 a charge is1 or produces1 a 'state of the ether' 7to use the unsatisfactory current phrase72 and the ether being capable of opposite distortions1 the effects upon it of opposite charges are contrary and similar1 though perhaps not equivalent2 whence the 'two fluid theory' obtains a prim facie recommendation as the simplest1 though a crude interpretation of electrical phenomena4 ,these are ubiquitous2 destitute though we are of sense-organs for their perception1 we still indirectly recognise their presence on every side4 ,if the unification of the forces in nature be attainable1 the unifying formula will doubtless be derived from them4 ,electricity is the mot de l'nigme2 yet it is itself the most inscrutable of enigmas4 ,,footnotes3 ,footnote #fb3 ,lorentz1 ,proceedings ,amsterdam ,academy1 #aijj1 p4 #efe4 ,footnote #fc3 ,sir ,w4 ,thomson1 ,philosophical ,magazine1 vol4 xlv41 fourth series1 #ahgc4 ,many hints have been taken1 in what is above written1 from this valuable paper4 ,footnote #fd3 ,sir ,w4 ,thomson 7,lord ,kelvin71 loc4 cit41 p4 #cbc4 ,footnote #fe3 ,electricity and ,matter1 p4 #aei4 ,footnote #ff3 ,loc4 cit41 p4 #cca4 ,footnote #fg3 ,trait de ,mcanique ,cleste1 tome4 iv41 p4 #die4 ,footnote #fh3 ,electricity and ,matter1 p4 #afj4 ,footnote #fi3 ,proceedings ,amsterdam ,academy of ,sciences1 #aijj1 p4 #eei4 ,footnote #gj3 ,monthly ,notices1 vol4 lxii41 p4 #fai2 vol4 lxiii41 p4 #beh4 ,footnote #ga3 ,monthly ,notices1 vol4 lxiii41 p4 #dbd4 ,footnote #gb3 ,j4 ,j4 ,thomson1 ,electricity and ,matter1 p4 #hh4 ,footnote #gc3 ,ibid41 p4 #dg4 ,,chapter ,,xi ,,the ,,inevitable ,,ether ,ether is the fundamental postulate of physics4 ,its existence1 nowise apparent1 is in all manner of ways implied4 ,the properties that must be assigned to it are certainly arduous of conception4 ,we need the aid of forced analogies to enable us to realize1 even imperfectly and indistinctly1 the mode in which it discharges functions obviously somehow discharged4 ,but in the last resort everything is obscure2 if our thought-borings go deep enough1 they always reach the incomprehensible4 ,the original ether was the 'quintessence' of the ancients--a kind of matter vaguely imagined as pure and incorruptible enough to serve for the raw material of the heavenly bodies1 the four common elements being reserved exclusively for sublunary use4 ,the distinction1 however1 eventually broke down4 ,all the spheres1 from the primum mobile to the very surface of our low earth1 are pervaded by a subtle mode of action1 demanding for its transmission machinery of a finer kind than could be constructed out of gross everyday matter4 ,the phenomena of light1 when they came to be attentively studied1 imperatively required a medium1 universally diffused1 evasive to sense1 accessible only by processes of reasoning4 ,hooke and ,newton accordingly brought the ether through the ,horn ,gate of dreamland into a region of reality1 where it became a subject of legitimate speculation to men of science4 ,the task1 nevertheless1 of definitely specifying its qualities was not taken seriously in hand until the beginning of the nineteenth century1 when the establishment of the undulatory theory of light supplied tangible holding-ground for ideas regarding the vehicle of propagation1 and rendered the ether a fixture of thought4 ,a great deal is demanded from it4 ,we cannot afford to set up an establishment of ethers2 one factotum must suffice4 ,incongruous offices are devolved upon it4 ,it has to be ,atlas and ,mercury in one4 ,it is the universal supporter and the universal messenger4 ,whatever kind of influence or form of energy can pass from world to world is conveyed by its means4 ,if 'action at a distance' be inadmissible 7as ,newton himself held it to be71 the pull of gravity must be exerted through a medium2 and common-sense insists upon its identification with the transmitting medium of light1 as well as upon the identification of that with the transmitting medium of electricity4 ,a genuine conformity to these demands of reason is vouched for1 not only by ,hertz's discovery that an electrical explosion starts an undulatory disturbance indistinguishable1 except in scale1 from luminous waves2 but also by ,dr4 ,lorentz's indicated conclusion that strains of the same ethereal essence bear the all-pervading mandates of gravity4 ,the unity of the medium may1 then1 be regarded as finally ascertained2 the complex interactions of sundry different 'fluids' need no longer be taken into account4 ,to provide one with the capabilities implied by the services we perceive it to render is1 indeed1 a sufficiently formidable task4 ,in popular apprehension the ether of space figures as a finer kind of air4 ,no idea could be more misleading4 ,the elasticity by which air transmits the longitudinal waves of sound is totally different from the elasticity by which ether propagates the transversal waves of light4 ,air yields to pressure2 disturbance hence produces in it undulatory condensations due to oscillations of the gaseous molecules along the line in which the audible commotion travels4 ,ether1 on the contrary1 appears to be entirely incompressible2 it conveys no vibrations directed lengthwise4 ,now this is extremely perplexing4 ,we have no experience of a kind of matter absolutely rigid to pressure1 while yielding1 albeit with intense reluctance1 to distortional stresses4 ,a jelly-like solid makes the nearest1 though a very distant1 approach to fulfilling the indispensable conditions2 and a solid ether was accordingly in vogue until long past the middle of the nineteenth century4 ,for a solid it had very peculiar qualities2 that1 for instance1 of offering no resistance to motion4 ,it was1 in truth1 obviously a mere temporary expedient--a scientific fiction which might pass muster until replaced by something corresponding less distantly with the fundamental fact4 ,at last1 on the advent of the electro-magnetic theory of light and the modified conceptions which it brought in its train1 the solid ether withdrew behind the scenes4 ,its properties1 though inconsistent and unconvincing1 had not been chosen arbitrarily2 they were imposed by the necessities of the situation2 and when these varied1 speculators naturally had recourse to fresh inventions4 ,the most plausible is that of a medium neither solid1 liquid1 nor gaseous in the ordinary sense1 but in the ideal state of a 'perfect fluid4' ,out of such an ether ,lord ,kelvin1 with exquisite ingenuity1 constructed his 'vortex-atoms1' which 'had their day and ceased to be4' ,other ideas now prevail4 ',the present tendency of physical science1' the late ,mr4 ,preston wrote in #ahij1gd 'is to regard all the phenomena of ,nature1 and even matter itself1 as manifestations of energy stored in the ether4' ,the more closely we look into the things around us1 the more strongly the persuasion is forced upon us that what we call ether1 electricity1 and matter are really varied forms of one primal substance4 ,two comprehensive schemes of molecular physics1 resting upon the basis of this unifying thought1 have lately been elaborated--one by ,dr4 ,larmor1 the other by ,professor ,osborne ,reynolds4 ,they have nothing in common beyond the largeness of their synthesis4 ,in every respect they are radically unlike1 save in regarding the intangible ether as the one material reality4 ,dr4 ,larmor1 however1 is not quite confidently explanatory4 ,he presents no cut-and-dried theory of the universe2 its haunting mysteries are not ignored in his efforts to rationalize them4 ,he is vividly aware of the difficulties besetting the endowment of the ether with the type of elasticity which it is recognised to possess4 ,he can only surmise that it results from particular modes of motion--from 'kinetic stability' ensuing upon a special dynamical state4 ,the medium may thus be thought of as pervaded by 'a structure of tangled or interlaced vortex filaments1 which might resist deformation by forming a stable configuration4'#ge ,but the details of any such scheme of action are evidently far too intricate to be easily unravelled2 what concerns us here is to point out that no simple structureless fluid can avail to maintain cosmical communications4 ,reduced to its lowest terms1 ,dr4 ,larmor's conception of the ether is that of a 'rotationally elastic medium4'#gf ,in other words1 it resists being turned round an axis4 ,the forces continually acting upon it are nevertheless of a gyratory nature2 and hence arise strains1 betrayed to our apprehension by electrical manifestations4 ,each 'electron' is held to be the nucleus of some kind of distortion or displacement1#gg and carries with it1 as it moves1 a field of force4 ,out of these 'point charges' material atoms are variously built up4 ,they are 'structures in the ether1' encompassed by 'atmospheres of ethereal strain1' not--as they were formerly taken to be--'small bodies exerting direct action at a distance on other atoms according to extraneous laws of force4'#gh ,obviously the new view brings to the front extremely subtle questions regarding the nature of 'dynamical transmission'#gi--what the propagation of energy essentially consists in1 and by what mechanism it is effected2 and they are1 for the present1 unanswerable4 ,electricity is1 on the theory we are attempting to sketch1 positive or negative according to the direction of the originating strain4 ,a positive electron might be imagined to resemble a spiral nebula of the right-handed sort1 a negative one a left-handed spiral1 or vice vers4 ,the analogy is1 perhaps1 fanciful2 yet it helps towards obtaining a mental picture of objects which1 insignificant and elusive though they appear1 may be the initials and ultimates of this strange world4 ,the forces1 at any rate1 by which it is at present kept going are evoked ad libitum by the pioneers of modern research from the ethereal plenum4 ,the actualities of matter are potentialities in the ether4 ',all mass1' in ,professor ,j4 ,j4 ,thomson's opinion1 'is mass of the ether1 all momentum1 momentum of the ether1 and all kinetic energy1 kinetic energy of the ether4#hj ,only if this be so1' he adds1 'the density of the ether must be immensely greater than that of any known substance4' ,the condition is startling1 but in dealing with such subjects we must be prepared to meet with anomalies4 ,they come1 as the ghosts appeared to ,odysseus in ,hades1 at first one by one1 then in an awe-inspiring swarm4 ,yet1 in spite of the perplexities they occasion1 we can discern1 with growing sureness of insight1 the amazing reality of the universal medium4 ,it is1 in a manner1 the only reality4 ,for what is manifest to sense is subject to change4 ,we can conceive that the visible framework of material existence might crumble and dissolve1 like 'the baseless fabric of a vision1' into seeming nothingness4 ,but a substance that is inapprehensible is1 to our limited ideas1 imperishable4 ,the ether is assuredly the seat of intense activities1 which lie at the root1 most likely1 of all the processes in ,nature4 ,an absolutely uniform medium1 however1 can scarcely be imagined to energize or react4 ,some kind of heterogeneity it must possess2 and the heterogeneity produced1 in ,dr4 ,larmor's view1 by strains1 is associated1 in ,professor ,reynolds's theory1 with intrinsic texture4 ,the ',sub-,mechanics of the ,universe' are here made to depend upon the fitting together of ineffably small1 ideally rigid grains4 ,a misfit gives rise to matter1 which might hence be defined as 'ether out of joint'2 and the misfit can be propagated endlessly from one range of granules to the next4 ,this propagation through the ether of an abnormal arrangement of its constituent particles1 without any transference of the particles themselves1 explains the phenomena of matter in motion4 ,a concrete existence belongs to the ether alone4 ,it is composed of round aboriginal atoms1 the diameters of which measure the seven hundred thousand millionth part of the wave-length of violet light4#ha ,they are packed closely together1 yet not so closely but that free paths are left to them averaging in length the four hundred thousand millionth part of their diameters4 ,this inconceivably small relative motion suffices1 nevertheless1 to render the medium elastic2 is1 indeed1 'the only cause of elasticity in the universe1 and hence is the prime cause of the elasticity of matter4' ,the medium so formed is ten thousand times denser than water2 it exerts a mean pressure of #gej1jjj tons on the square inch2 the coefficient of its transverse elasticity is #i #ajbd 7in ,c4,g4,s4 units72 which gives a velocity of transmission identical with that of light for vibrations of the same type1 while longitudinal waves are propagated #bd times more rapidly4 ,the scheme further includes a plausible rationale of gravity and of electrical effects2 so that there is much to warrant the claim of its author to have excogitated 'the one and only conceivable purely mechanical system capable of accounting for all the physical evidence1 as we know it1 in the universe4' ,the machine1 to be sure1 lacks motive power2 but that is a want which no human ingenuity can supply4 ,its source is obscured in the primal mystery of creation4 ,and as regards the preliminary assumptions required for the constitution of an atomic ether1 inclined though we might be to cavil at them1 we should1 perhaps1 act more wisely in following ,dr4 ,larmor's advice by abstaining from attempts to explain 'the simple group of relations which have been found to define the activity of the ether4 ,we should rather rest satisfied1' he tells us1 'with having attained to their exact dynamical correlation1 just as geometry explores or correlates1 without explaining1 the descriptive and metric properties of space4'#hb ,yet one cannot help remarking that the properties of space are not ordinarily modified to suit the needs of demonstration1 while those of the ethereal medium are varied at the arbitrary discretion of rival cosmogonists4 ,in the future1 when they come to be more clearly ascertained1 they will1 perhaps1 form the basis of a genuine new science4 ,already1 the study of ethereal physics excites profound interest and attention4 ,nor is it possible to ignore the gathering indications that it will impose qualifications upon principles consecrated by authority and hitherto regarded as fundamental4 ,the grand modern tenet of the conservation of energy1 for example1 may need a gloss2 it may prove to be admissible only with certain restrictions4 ,the second bulwark of the scientific edifice is even more seriously undermined4 ,for the 'strain theory' of atomic constitution necessarily includes the conception of opposite distortions corresponding to positive and negative electricity4 ,and the further inference lies close at hand that these1 by combining1 may neutralize one another4 ,the coalescence1 then1 of a positive and negative electron should result in the smoothing out of the complementary strains they stand for2 and there would ensue the annihilation of a pair of the supposed ultimates of matter4 ,the event might be called the statical equivalent of the destruction of light through interference4 ,that its possibility should be contemplated even by the most adventurous thinkers is a circumstance fraught with meaning as to the subversive tendencies of recent research4 ,already1 in ,may1 #aijb1 ,professor ,j4 ,a4 ,fleming#hc pointed out that 'if the electron is a strain-centre in the ether1 then corresponding to every negative electron there must be a positive one4 ,in other words1 electrons must exist in pairs of such kind that their simultaneous presence at one point would result in the annihilation of both of them4' ,the consequence thus viewed in the abstract finds concrete realization1 if ,mr4 ,jeans's suggestion be adopted1#hd in the processes of radio-activity1 which possibly consist 'in an increase of material energy at the expense of the destruction of a certain amount of matter4 ,there would1 therefore1 be conservation neither of mass nor of material energy4' ,no longer ago than at the opening of the present century such notions would have been scouted as extravagant and paradoxical2 now there is no escape from giving them grave and respectful consideration4 ,scientific reason has ceased to be outraged by hypotheses regarding the disappearance of mass and the development of energy4 ,mass and energy may1 after all1 be interchangeable2 they are1 at any rate1 kept less rigidly apart in our meditations than used formerly to be the case4 ,nor can we assert with any confidence that partial subsidences into or emergences from the surrounding medium are for either a sheer impossibility2 the universal framework1 on the contrary1 presents itself to us in the guise of an iridescent fountain leaping upward from1 and falling back towards1 the ethereal reservoir4 ,to the very brink of that mysterious ocean the science of the twentieth century has brought us2 and it is with a thrill of wondering awe that we stand at its verge and survey its illimitable expanse4 ,the glory of the heavens is transitory1 but the impalpable1 invisible ether inconceivably remains4 ,such as it is to-day1 it already was when the ,fiat ,lux was spoken2 its beginning must have been coeval with that of time4 ,nothing or everything1 according to the manner in which it is accounted of1 it is evasive of common notice1 while obtrusive to delicate scrutiny4 ,its negative qualities are numerous and baffling4 ,it has no effect in impeding motion2 it does not perceptibly arrest1 absorb1 or scatter light2 it pervades1 and may even share in the displacements of gross matter2 yet its motion 7if it do move71 is without effect on the velocity of light4 ,looking1 however1 below the surface of things1 we find the semi-fabulous quintessence to be unobtrusively doing all the world's work4 ,it embodies the energies of motion2 is1 perhaps1 in a very real sense1 the true primum mobile2 the potencies of matter are rooted in it2 the substance of matter is latent in it2 universal intercourse is maintained by means of the ether2 cosmic influences can be exerted only through its aid2 unfelt1 it is the source of solidity2 unseen1 it is the vehicle of light2 itself non-phenomenal1 it is the indispensable originator of phenomena4 ,a contradiction in terms1 it points the perennial moral that what eludes the senses is likely to be more permanently and intensely actual than what strikes them4 ,,footnotes3 ,footnote #gd3 ,theory of ,light1 second edition1 p4 #bh4 ,footnote #ge3 ,encyclopdia ,britannica1 vol4 xxv41 p4 #ajf4 ,footnote #gf3 ,report of the ,british ,association1 #aijj1 p4 #fbf4 ,footnote #gg3 ther and ,matter1 p4 #bf4 ,footnote #gh3 ,nature1 vol4 xlii41 p4 #dec4 ,footnote #gi3 ,larmor1 ,report ,british ,association1 #aijj1 p4 #fbe4 ,footnote #hj3 ,electricity and ,matter1 p4 #ea4 ,footnote #ha3 ,the ,structure of the ,universe1 ,rede ,lecture1 ,june #aj1 #aijb1 p4 #ad4 ,footnote #hb3 ,nature1 ,june1 vol4 lxii41 p4 #dea4 ,footnote #hc3 ,proceedings of the ,royal ,institution1 vol4 xvii41 p4 #agg4 ,footnote #hd3 ,nature1 vol4 lxx41 p4 #aja4 ,,chapter ,,xii ,,the ,,forms ,,of ,,nebul ,sir ,william ,herschel's celestial surveys first made the classification of nebul practicable4 ,until he began grinding specula at ,bath very few such objects were known1 and those too imperfectly for the effectual discrimination of their differences4 ,arrangement presupposes comparison1 and comparison some variety of specimens to be compared1 which became available only through ,herschel's scrutiny4 ,the rapidity and penetrative power of his observations in this field almost passes belief4 ,he detected with discernment4 ,discovery and enrolment did not satisfy him2 he was1 besides1 keen to note analogies and contrasts1 likenesses and dissimilitudes4 ,he could not see without at the same time setting in order what he saw2 and the law of order that commended itself to him was founded on an evolutionary principle4 ,the contents of the heavens seemed to fall spontaneously1 as he regarded them1 into genetic sequences2 and the nebul with particular facility4 ,the criterion adopted was that of progressive condensation4 ,development must clearly1 he judged1 be attended by contraction and local brightening4 ,diffused milky tracts represented cosmic formations in their most rudimentary form2 they assumed1 through the unremitting action of gravity in drawing their particles together1 a more compact texture1 more definite shapes1 and a heightened lustre4 ,but things have changed somewhat in aspect during the last hundred years4 ,herschel's simple regulative plan1 although of unquestioned validity1 needs to be supplemented and controlled4 ,much auxiliary knowledge has been acquired since it was formulated4 ,in attempting to estimate the comparative antiquity of nebul1 we no longer depend exclusively upon one set of indications4 ,the conclusions drawn from their immediate inspection can at least be checked by the study of their spectra and distribution4 ,the ,milky ,way might be figuratively described as the nursery-garden from which the parterres of the universe are stocked4 ,a primitive condition is usually assigned1 not without good reason1 to any class of objects markedly tending to collect in its plane4 ,and this is the case with gaseous or 'green' nebul4 ,moreover1 their materials appear to be in a highly elementary state 7if it be permissible to speak of one kind of matter as more elementary than another72 their spectra including no rays due to metallic incandescence1 but mainly those of nebulium1 hydrogen1 and helium4 ,these substances1 inconceivably attenuated1 constitute the vast irregular formations placed by ,herschel at1 or near1 the start of cosmical development4 ,and so far he has been justified by the outcome of modern research4 ,but he has not been justified in his description of planetary nebul as 'very aged1 and drawing on towards a period of change or dissolution4' ,for1 despite their determinate shape and definite boundaries1 they do not appreciably differ in composition from nebul of the irregular class1 and must be reckoned as1 in a manner1 coeval with them4 ,there is1 on the whole1 a concurrence of evidence that gaseous nebul are at a very early stage of growth4 ,they are the least elaborated of sidereal objects2 they seem1 many of them1 barely to have crossed the threshold of creation4 ,yet their mutual relations in time are by no means obvious4 ,they cannot easily be disposed in any kind of rational sequence4 ,each of the great nebul1 at any rate1 exhibits features and occupies a position shared by none of its fellows4 ,the most discerning cosmologist cannot pretend to say that the ,argo nebula1 say1 is of greater or less antiquity than the ,orion or the ',america' nebula4 ,they are individual growths1 simultaneous1 not successive4 ,the line of development suggested by their relationships is rather towards the formation of star-clusters than of diverse nebular species4 ,thus1 the ,pleiades illustrate not improbably the future condition of the ,orion nebula1 the contained stars having gained predominance over their misty envelopments1 though fragmentary swaddling-bands1 later1 presumably1 to be shaken off1 still adhere to many of them4 ,planetary nebul have much more in common than irregular nebul1 and their minor varieties might1 with some plausibility1 be associated with differences in relative age4 ,they are marked chiefly by the character of the nuclear star which1 in nearly all such objects1 appears to act as the pivot of the surrounding vaporous structure4 ,the supposition lies close at hand that it is designed as a provision for the nourishment of the star--that the star gains in mass and light at the expense of the nebula1 which it is eventually destined wholly to absorb and supersede4 ,on this view1 planetaries like the green glow-lamp at the pole of the ecliptic 7,n4,g4,c4 #f1edc7 should be regarded as the most advanced1 while ,webb's planetary in ,cygnus 7,n4,g4,c4 #g1jbg7 would exemplify an inchoate condition4 ,in the former the central star is of #if magnitude1 and sharply stellar2 in the latter it is double and diffuse1#he perhaps a wide binary system in embryo4 ,the question is1 however1 still open as to the real nature of the connection between planetaries and their central stars4 ,the pabulum theory is a promising conjecture2 but no facts with which we are acquainted stringently enforce it4 ,ideas on the subject will need complete revision if the traces of spirality noted from time to time in some of these peculiar objects prove to be of radical significance4 ,the oculi1 distinctive of the ',owl nebula' 7,n4,g4,c4 #c1ehg71 as originally shown by the ,parsonstown reflector1 consisted of luminous traceries coiled round two interior stars1#hf but the appearance was either due to illusion1 or became effaced by change1 since the camera has refused to endorse it as genuine4 ,the 'helical' planetary in ,draco#hg is doubtless essentially a spiral conformation2#hh and ,professor ,schaeberle1 by means of exposures with a #ac-;inch reflector of #bj inches focus1 has compelled1 not only the ,ring nebula in ,lyra1#hi but the ,dumb-bell in ,vulpecula1 to betray the surprising secret of their whorled structure4 ,both these nebul give a spectrum of bright lines1 and inventiveness is at a loss to devise means for building up gaseous materials into edifices of strongly characterized architectural forms4 ,the materials1 indeed1 may not be wholly gaseous2#ij or we possibly see 7as ,professor ,darwin long ago suggested7 merely illuminated stream-lines of motion furrowing an obscure mass4 ,but if this be indeed so1 there is the further question to be asked3 ,what direction does the motion take8 ,do the tides set inward or outward8 ,our spontaneous impressions are all in favour of concentrative tendencies4 ,we cannot easily shake off centripetal prejudices4 ,our lives are passed under a regimen of central attraction1 and we naturally incline to universalize our experience4 ,herschel's scheme of sidereal evolution invites accordingly at first sight ready acceptance4 ,stars seem as if they could not act otherwise than as foci of condensation in nebul2 the lucid stuff involving them must1 apparently1 with the lapse of ages1 settle down towards their surfaces1 and become absorbed into their substance4 ,such processes1 indeed1 belong1 unless counteracted by different modes of action1 to the inevitable order of nature2 but these may1 and probably do1 exist4 ,from sundry quarters the conviction is pressed upon us that cosmic bodies can drive out matter as well as draw it in4 ,repulsive forces insist upon recognition1 and their effects become more palpable the more attentively they are considered4 ,under certain conditions they get the better of gravity2 and stars may possibly1 like cocoon-spinning insects1 expend their organic energies in weaving themselves faintly lucent envelopes1 the products of subtle and unaccountable activities4 ,the example of ,nova ,persei is fresh in every mind1 but we make no pretension to decide the controversy it raised4 ,a dogmatic pronouncement is unadvisable where the unknown elements of the question obscure and outweigh those that are known4 ,a less slippery foundation for reasoning is afforded by the permanently visible spiral nebul1 and features charged with an emphatic meaning have been revealed in them by photographic means4 ,looking at the entire contents of the nebular heavens1 we find the spiral type very largely predominant4 ,it claims more specimens1 and emerges more distinctly with each development of delineative power4 ,its chief prevalence is among 'white' nebul1 showing continuous spectra4 ,they are vastly numerous4 ,gaseous nebul are reckoned by the score1 white nebul by tens of thousands4 ,moreover1 they collect near the poles of the ,milky ,way1#ia while the gaseous variety crowd towards its plane1 both branches of the family thus manifesting galactic relationships1 though of an opposite character4 ,now1 these facts of distribution have some bearing on the question of relative age4 ,there is1 as already remarked1 a consensus of opinion that objects showing a marked preference for the ,milky ,way are in a more primitive state than those withdrawn from it1 and the inference is supported by the circumstance that nebul situated in high galactic latitudes shine with continuous light1 those near the galactic equator with vivid lines4 ,yet it would be rash to assume that any individual nebula traverses these successive stages4 ,the series would be satisfactorily established only if we could point to a number of intermediate instances1 which seem to be almost wholly lacking4 ,we cannot trace in nebular as we can in stellar growth the insensible gradations of progressive change4 ,they are perhaps complicated in nebul by influences of a different kind from those which have gained the ascendancy in stars4 ,diffusive effects may in them be more conspicuous than concentrative effects2#ib or a balance may be temporarily struck between antagonistic tendencies4 ,spiral conformation is the real crux of nebular cosmogony4 ,the conditions from which it arises are met with only in the sidereal heavens1 but are there widely prevalent4 ,though remote from our experience1 they are fundamental in the realms of space4 ,if we could define and comprehend them1 we should be in a better position for determining the cosmical status of nebul4 ,the choice is open between two rival theories of nebulous spirals4 ,the first is the more obvious1 and readily falls in with admitted mechanical principles4 ,sir ,robert ,ball has adopted and ingeniously advocated this view4 ,a globular collection of promiscuously revolving particles inclines1 if left to itself1 to flatten down into a disc4 ,the reason is this3 ,in a system of the kind moment of momentum is invariable1 while energy constantly diminishes4 ,to render the contrast intelligible we have only to consider that moment of momentum is the algebraic sum of all the products of mass and motion in the aggregation1 reduced to1 or projected upon1 its 'principal plane1' while energy is independent of the varied directions of velocity4 ,collisions consequently involve no diminution of moment of momentum1 but combine with radiative waste to produce a steady loss of energy4 ,inevitably1 then1 the system will assume the form in which it possesses the minimum of energy that is consistent with the maintenance of its original momentum2 and it is that of a disc extended in the principal plane4 ,retrograde movements will by the time this shape is definitively arrived at have become eliminated2 the constituent particles circulate unanimously in one direction2 and ,sir ,robert ,ball adds that their circulation1 owing to the more rapid rotation of the central mass1 is along spiral paths4#ic ,they would accordingly present the twisted conformation so commonly observed in the heavens1 and might even include subordinate centres of attraction1 fitted to ripen and strengthen into a full-blown retinue of planets4 ,such are spiral nebul regarded in their direct mechanical aspect4 ,spherical nebul are their immediate progenitors2 suns1 with or without trains of dependent worlds1 their lineal descendants4 ,let us1 however1 consult some autographic records and weigh attentively what these peculiar objects tell us about themselves4 ,we see at once that their curving lines1 far from being laid down at the dictate of chance1 follow a strictly defined plan4 ,spiral nebul are not formed like watch-springs by the windings of a single thread4 ,they are always two-branched4 ,from opposite extremities of an elongated nucleus issue a pair of nebulous arms1 which enfold it in double convolutions4 ,their apparent superposition and interlacements occasion1 in the ,lyra nebula1 the noted effect of a fringed and ruptured annulus1 and it is of profound interest to perceive that even in gaseous masses the same constructive rule prevails as in the great ,whirlpool in ,canes ,venatici4 ,yet this circumstance is well-nigh irreconcilable with the hypothesis that an influx of material is in progress4#id ,falls due to gravity could not be limited to two narrow areas on the central body4 ,matter ejected from it might1 on the other hand1 quite conceivably follow this course4 ,interior strain could easily be supposed to cause yielding along a given diameter1 and nowhere else4 ,solar disturbances partially and dimly illustrate such a kind of activity4 ,diametrically opposite prominences are not unknown4 ,they indicate the action of an explosive force right across the solar globe4 ,similarly1 the formation of a spiral nebula cannot be rightly apprehended otherwise than as the outcome of long-continued1 oppositely-directed eruptions4 ,the history of the heavens involves the law of spirality4 ,the scope of its dominion continually widens as research becomes intensified4 ,the ,huygenian 'portent' in the ,sword of ,orion now figures as merely the nucleus of the 'great winding ,nebula' photographed by ,professor ,w4 ,h4 ,pickering in #ahhi4 ,that the vast nebulosity encompassing the ,pleiades is an analogous structure seems eminently probable1 though the brilliancy of the enclosed stellar group obliterates most traces of its ground-plan4 ,the magnitude of the mixed system1 we are told by ,professor ,barnard1#ie who detected it in #ahic by means of a ten hours' exposure with the ,willard lens1 transcends our powers of realization4 ,it covers #ajj square degrees of the sky with intricate details4 ,again1 some four minutes of arc to the north-west of the ,ring in ,lyra lies a small nebula discovered visually by ,professor ,barnard in #ahic1 and photographically resolved by ,keeler into a delicate spiral4 ,it is a two-branched1 left-handed spiral1 as the large adjacent object has also proved to be4 ,one is1 in fact1 the miniature of the other1 and they are now shown1 by ,professor ,schaeberle's short-focus reflector1 to be linked together by curving folds of nebulosity into a compound spiral system4 ,the ,dumb-bell is held1 on the same authority1 to be similarly conditioned1 and the analogy frequently noted between its aspect and that of the ,ring nebula has thus become incalculably widened in scale4 ,the galactic relations of the ,magellanic ,clouds are not easily defined4 ,they are within the ,milky ,way1 yet not of it4 ,enigmatical excrescences upon the universe1 they suggest an origin from gigantic eddies in the onflowing current of sidereal arrangement4 ,their miscellaneous contents are1 to all appearance1 disposed along eddying lines4 ,mr4 ,h4 ,c4 ,russell's photographs#if rendered this1 in #ahij1 to some extent manifest1 and their indications were ratified by the ,arequipa plates1 from the study of which ,professor ,pickering gained the conviction that the great ,looped ,nebula1 #cj ,dorads1 is the structural nucleus of the ,nubecula ,major4 ',it seems1' he wrote1#ig 'to be the centre of a great spiral1 and to bear the relation to the entire system that the nebula in ,orion bears to the great spiral nebula which covers a large part of that constellation4' ,on all sides1 in the sidereal heavens1 we can discern the signs of the working of a law of convolution4 ,sometimes they are patent to view2 sometimes half submerged2 but they can generally1 with attention1 be disentangled from overlying appearances4 ,they are exhibited by stars no less than by nebul1 as the late ,dr4 ,roberts pointed out from convincing photographic evidence2 the 'hairy' appendages of globular clusters betray them by their curvilinear forms2 they meet us in every corner of the wide nebular realm4 ,many investigators recognise in the ,milky ,way itself the stamp of spirality4 ,stephen ,alexander1 of ,new ,jersey1#ih regarded the majestic galactic arch as a four-branched spiral1 resulting from catastrophic breaches in a primitive1 equatorially loaded spheroid1 the currents of matter ejected by which should1 owing to their lower angular rotation1 lag behind as they retreated from the nucleus1 and thus flow along helicoidal lines4 ,r4 ,a4 ,proctor subsequently devised convoluted galactic streams1 which1 however1 corresponded imperfectly with what the sky showed4 ,and ,dr4 ,easton#ii has designed by way of simple illustration an elaborate series of spires1 originating possibly from a central galactic condensation1 the projection of which upon the sphere may1 he thinks1 account for the known peculiarities of the ,milky ,way4 ,our interior situation1 nevertheless1 makes it extremely difficult to determine the real relations in space of the star-streams circling around it4 ,the observed facts are1 perhaps1 equally compatible with many other structural schemes besides those based on the idea of spirality2 and it will be prudent to adopt none1 for the present1 with settled conviction4 ,we can1 however1 gather one sufficiently definite piece of information regarding the history of the ,cosmos4 ,all the inmates of the heavens1 stellar and nebular1 represent quite evidently the dbris of a primitive rotating spheroid4 ,its equator is still marked by the galactic annulus1 its poles by a double canopy of white nebul4 ,the gyrating movement which it once possessed as a whole doubtless survives in its parts1 but ages must elapse before the fundamental sidereal drift can be elicited4 ,,footnotes3 ,footnote #he3 ,keeler1 ,lick ,publications1 vol4 iii41 p4 #bad4 ,footnote #hf3 ,rosse1 ,transactions ,royal ,dublin ,society1 vol4 ii41 p4 #ic4 ,footnote #hg3 ,first detected as such by ,holden and ,schaeberle in #ahhh1 ,monthly ,notices1 vol4 xlviii41 p4 #chh4 ,footnote #hh3 ,deslandres1 ,bulletin ,astronomique1 ,february1 #aijj4 ,footnote #hi3 ,astronomical ,journal1 ,nos4 #eci1 #edg4 ,footnote #ij3 ,maunder1 ,knowledge1 vol4 xix41 p4 #ci4 ,footnote #ia3 ,dr4 ,max ,wolf places the point of nebular concentration in ,r4,a4 #ab;h #ecm1 ,d4 #fa #bj1 that assigned to the galactic pole being in ,r4,a4 #ab;h #dim1 ,d4 #fb4 ,knigstuhl ,publ41 ,bd4 ,i41 p4 #agd4 ,footnote #ib3 ,t4 ,j4 ,j4 ,see1 ',repulsive ,forces in ,nature1' ,popular ,astronomy1 ,no4 #ajj1 ,december1 #aijb4 ,footnote #ic3 ,the ,earth's ,beginnings1 pp4 #bdc-bdg4 ,footnote #id3 ,cf4 ,moulton1 ,astrophysical ,journal1 vol4 xxii41 p4 #afe4 ,footnote #ie3 ,monthly ,notices1 vol4 lx41 p4 #bei4 ,footnote #if3 ,see ,knowledge1 vol4 xiv41 p4 #ej4 ,footnote #ig3 ,harvard ,annals1 vol4 xxvi41 p4 #bjf4 ,footnote #ih3 ,astronomical ,journal1 vol4 ii41 p4 #ajj1 #aheb4 ,footnote #ii3 ,astrophysical ,journal1 vol4 xii41 p4 #aeh4 ,,chapter ,,xiii ,,the ,,procession ,,of ,,suns ,phenomena are functions of time1 and the form of the function has to be determined in each particular case4 ,that is what the historical method comes to1 and its use is prevalent and almost compulsory4 ,we can no longer be satisfied with a simple bird's-eye view of the universe2 our thoughts are irresistibly driven to grope into its past1 and to divine its future4 ,statical conceptions sufficed for our intellectual forefathers4 ,they aimed at establishing the equilibrium of things1 while we see them in a never-ending flux4 ,one aspect of them calls up the next1 and that another1 and so on ad infinitum2 we cannot1 if we would1 balance our ideas on the pivot of the transient present4 ,the immutable heavens of the ancients strike us to-day as the invention of a strange race of beings4 ,we see them1 on the contrary1 with ,shelley as a 'frail and fading sphere1' a 'brief expanse1' the seat and scene of change4 ,the 'fixed' stars long ago broke away from their moorings1 and began to flit at large through space4 ,of late a less obvious1 more intimate kind of mobility has been attributed to them4 ,grooves of individual development have been assigned to them1 along which they appear to shift as the tardy ages go by2 and since everything that grows must decay1 the orbs of heaven1 too1 incur the doom of mortality4 ,but modern science has done much more than extend to them the dismal philosophy of the phrase1 ',tout passe1 tout casse1 tout lasse4' ,the grandiose enterprise has been not unsuccessfully essayed of tracing in detail the progress of sidereal evolution1 and of marshalling the vast stellar battalions in order of seniority4 ,this has been rendered feasible by the disclosures of the spectroscope4 ,apart from their guidance1 the track might have been seen by elusive glimpses1 but could never have been laid down with any approach to definiteness4 ,herschel found for it a terminus quo in nebul of various forms1 but attempted to pursue it no further4 ,we do not hesitate to run it on1 from station to station1 right down to the terminus ad quem4 ,not1 it is true1 without the perception of outstanding difficulties and insecurities1 which yet seem to be outweighed by a certain inevitableness of self-arrangement in the related facts4 ,the argument from continuity is that mainly relied upon4 ,an unbroken succession of instances is strongly persuasive of actual transition1 provided only that a principle of development 7so to call it7 may reasonably be assumed as influential4 ,a series of mineralogical specimens1 however finely differenced1 does not suggest the progressive enrichment of one original mass of ore4 ,in the stars1 on the other hand1 a species of vitality may be said to reside4 ,they are not finished-off products1 but spontaneously-acting machines4 ,they are centres of energy1 which they dispense gratis1 supplying the cost out of their own funds4 ,and the process is not only obviously terminable1 but must be accompanied by constitutional alterations1 which might be traceable by subtle methods of inquiry4 ,they are traceable1 unless we are deceived by illusory appearances4 ,secchi's classification of the stars was unwarped by any speculative fancy4 ,it was purely formal2 it aimed only at providing distinct compartments for the convenient arrangement of a multitude of differently characterized items of information4 ,then1 by degrees1 the closeness of the gradations between one class and the next came to be noticed2 partitions melted away2 the methodized array showed itself to be in movement2 and the bare framework took shape1 under the auspices of ,zllner and ,vogel1 as a cosmic pedigree4 ,the white stars were set forth as the progenitors of yellow1 yellow of red stars2 and the insensibly progressive reinforcement of the traits of relationship between the successive types went far towards demonstrating some partial1 if not a complete1 correspondence of the indicated order with the truth of things4 ,it has since been found necessary to divide the first stellar class into helium and ,sirian stars2 and here1 too1 essential diversity shades off imperceptibly into likeness approximating to identity4 ,all the groups hang together2 the entire scheme is on an inclined plane of change4 ,helium stars1 as they condense1 pass into ,sirian1 these into solar stars1 which finally1 reddening through the increase of absorption1 exhibit the badge of post-meridional existence in fluted spectra4 ,the finality of the red stage is1 indeed1 very far from being absolute1 but what lies beyond is matter of conjecture4 ,there are several good reasons for taking helium stars to be the 'youngest' or most primitive of the amazing assemblage that sparkle in the vault of heaven4 ,the first is their affinity with nebul4 ,every star1 perceived to be involved in folds or effusions of shining haze1 has yielded--if bright enough for profitable examination--a spectrum of helium quality4 ,further1 they are remarkably tenuous bodies4 ,it has been ascertained with approximate certainty1 from the investigation of stellar eclipses1 that helium stars are commonly1 perhaps invariably1 of far slighter consistence than the sun4 ,radiation1 however1 is maintained by contraction2 hence1 orbs at the outset of their course must be1 on the whole1 the most diffuse4 ,a third note of youth is membership of embryo systems1 and this is affixed very markedly to helium stars4 ,one-third certainly1 probably one-half of those lately submitted to trial by ,professors ,frost and ,adams proved to have spectroscopic companions4 ,they are pairs believed to have been recently divided by the fission of a single parent-globe4 ,and this is an operation which must1 we should suppose1 be undergone early1 or not at all4 ,the spectra of helium stars are peculiar and suggestive4 ,those belonging to ,miss ,maury's earliest groups--many of them visibly nebulous--bear next to no traces of metallic absorption1 showing instead lines of oxygen1 of nitrogen1 and of hydrogen in all its three series4 ,the conditions1 accordingly1 needed to produce the 'cosmic' modification of hydrogen are realized in these inchoate bodies4 ,what those conditions actually are we cannot tell1 yet it may be confidently surmised that they will prove to be of an electrical nature4 ,hydrogen resembles the metals in being electro-positive2 it collects at the negative pole during the electrolytic decomposition of water4 ,there is1 however1 an unmistakable tendency in primitive sidereal objects to display absorption rays of electro-negative rather than of electro-positive elements4 ,it is conceivable that hydrogen may be capable of altering its behaviour in this respect1 and that the molecules radiating the ,pickering and ,rydberg series1 in addition to the more familiar ,huggins series1 have1 in fact1 through some corpuscular re-arrangement1 assumed the electro-negative quality properly characterizing a non-metallic substance4 ,the association of this form of hydrogen with oxygen and nitrogen in early helium stars would thus be naturally related to the simultaneous quasi-disappearance from them of the spectral badges of metals4 ,the helium-line most distinctive of this stellar family is situated well up in the blue4 ,it appertains to the same vibrational sequence with ,d#c1 which is also represented in ,rigel1 one of the more 'advanced' ,orion stars4 ,in ,rigel1 too1 we meet a fairly prominent magnesium ray1 lying below the blue helium emanation1 while as yet iron is unapparent4 ,numerous fine1 faint streaks1 due to its absorption1 only emerge when the ,sirian type is fully reached1 and they are mostly of the 'enhanced' kind4 ,when the spark discharge is substituted for the arc as the source of illumination1 certain lines in the resulting spectrum brighten relatively to the others1 and these have been distinguished by ,sir ,norman ,lockyer as 'enhanced4' ,now1 the rule is strikingly prevalent that the absorption rays in white stars are of this class2 yet it can no longer be interpreted as indicating for them an excessively high temperature4 ,rather1 it would seem that electrical conditions still imperfectly defined are in question1 and their gradual removal or subsidence is1 beyond doubt1 largely instrumental in bringing about the transition to the solar stage4 ,the effacement of helium-absorption is even more perplexing4 ,no sooner does iron begin to show than it vanishes4 ,there is still a faint trace of its 'blue' line in ,vega2 none survives in ,sirius4 ,in spectra of the solar type two great bars of violet light are stopped out by calcium2 otherwise metallic arc-lines predominate1 while those of hydrogen are no longer so powerfully emphasized as in white stars4 ,moreover1 the whiteness of the unveiled ,sirian photospheres has become tinged with yellow owing to the development of a shallow envelope partly impermeable to blue rays4 ,for this reason the comparative extension of their ultra-violet spectra affords1 for stars of different types1 no secure criterion of relative temperature4 ,sound in principle1 it becomes inapplicable when the unknown factor of general absorption comes into play4 ,the energy-curve of the solar spectrum1 as it is1 can be determined2 the energy-curve of the solar spectrum1 as it would be if unaffected by general absorption1 has to be constructed from inference4 ,but only photospheres bare to space give comparable results4 ,hence1 there are no valid grounds for asserting that ,sirius is hotter than the sun1 or the sun than ,betelgeux4 ,it may be so1 but the evidence at present available is inconclusive4 ,the appearances expounded in this sense may bear quite different meanings4 ,the reasons for holding that solar mature into ,antarian stars are of the same character1 and of equal cogency with those tending to prove their own development from luminaries of ,sirian type4 ,there is a similar continuity of specimens4 ,they can be ranged one after another in an unbroken series1 in which1 as we run down the line1 primrose shades into orange1 and orange into red2 general absorption arrests an increasing percentage of the blue radiations1 while specific absorption becomes strengthened by dusky channellings of titanium4 ,carbon stars are less easily located4 ,dr4 ,vogel regards them as co-ordinate with the ,antarian class4 ,the two varieties of red stars with banded spectra descend1 in his opinion1 from the common stock exemplified by our sun4 ,professor ,hale also favours this view1 some attendant difficulties notwithstanding4 ,his photographs have certainly established for carbon stars links of relationship both with the ,antarian and the solar families2 yet the fact remains indisputable that the carbon type is1 to a great extent1 isolated from all the rest4 ,tokens of a genuine migration towards it are few and obscure4 ,the ultimate fate of both tribes of red stars can only be conjectured4 ,most of the objects constituting them vary in brightness1 some to the verge of periodical extinction2 and variability may be a symptom of interior dilapidation4 ,but the organization of such bodies is profoundly enigmatical4 ,they are exceptionally remote1 and offer slight holding-ground for inquiry4 ,no indications have been gathered as to their density or intrinsic light-power4 ,very little is known about their movements4 ,they rarely form binary combinations1 and those that they do form are almost always relatively fixed4 ,no red star travels in a computed orbit2 only one1 ,geminorum1 occurs on the long list of spectroscopic binaries4 ,the revolutions of this curious system ought to prove1 when thoroughly investigated1 replete with interest and instruction4 ,coupled stars present special opportunities to students of cosmogony4 ,they are obviously contemporaries2 they have started fair in the evolutionary race2 identical influences have acted upon them2 hence1 differences in their standing can only result from dissimilarities in mass or composition4 ,it is commonly taken for granted that a body containing less matter than its fellow must develop faster1 and incur the final quenching sooner4 ,but ,sir ,william and ,lady ,huggins have adverted to the probability of the very opposite being the case4 ,powerful surface-gravity may1 they consider1 serve to hasten the transition from a ,sirian to a solar spectrum2 and we should then have giant suns like ,capella1 advanced in type while at a very early stage of condensation4 ,this perhaps explains the remarkable spectral relations of contrasted stellar pairs4 ,always1 so far as we yet know1 the ,sirian spectrum is yielded by the lesser star1 the mass of which1 judging by analogy1 must be even smaller than would be indicated by the proportion of its faintness4 ,it is true that the distribution of mass in binary systems is often widely different from what might have been anticipated4 ,certain purplish satellites1 for instance1 of undetermined spectral quality exercise a gravitative sway of surprising force4 ,some results of this kind lately obtained by ,mr4 ,lewis and others are likely to prove of fundamental importance to theories of stellar evolution4 ,what we know of 'dark stars' has been mainly derived from the observation of stellar systems4 ,they are assumed to be the denizens of a stellar ,hades1 dim wanderers amid the shades1 who 'have had their day1 and ceased to be' as suns4 ,in the 'cold obstruction' of these viewless orbs the grand cosmical procession is held to terminate4 ,their presence attests the downward progress of decay1 and gives logical completeness to the argument for development4 ,yet there are circumstances warning us against too full an assurance that their status is really that of skeletons at the feast of light4 ,they are very frequently found to be in close attendance upon brilliant white stars4 ,thus intimately1 if incongruously1 coupled1 they circulate and compel circulation in brief periods1 as members of systems just1 it might be said1 out of the shell4 ,what are we to think1 for instance1 of the obscure body spectroscopically discovered to control the revolutions of the chief star in the ,orion trapezium8 ,it is evidently comparable in mass with that imperfectly condensed luminary4 ,is it credible that it has already traversed all the stages of stellar existence1 and cooled down to planetary rank8 ,so violent an assumption should at least not be made without due consideration2 and we may more prudently hold our judgment in suspense as to whether globes so circumstanced--and they abound--should be regarded as effete1 or as abortive suns4#ajj ,speculations on the exhaustion of stellar vitality have lately become inextricably involved with the complex problem of elemental evolution4 ,a dim inkling has been acquired of the activity in the universe of obscure forces1 availing1 we can just see1 to falsify many forecasts4 ,the theory1 among others1 of the dissipation of energy needs to be revised or qualified4 ,nor was it propounded by ,lord ,kelvin with dogmatic certainty4 ,he carefully noted the possibility that in 'the great storehouses of creation' reserves of energy might be provided by which the losses incurred through radiation could be1 wholly or in part1 made good4#aja ,the anticipated possibility is perhaps realized in the phenomena of radio-activity4 ,but if we inquire how1 we are met at the threshold by difficulties connected with the origin of helium4 ,helium appears to result from the disintegration of radium1 its generation being accompanied by the setting free of enormous quantities of energy4 ,its copious presence1 then1 argues long-continued and lavish expenditure of heat and light4 ,yet it is as a constituent of highly primitive orbs that it is chiefly conspicuous4 ,gaseous nebul1 too1 include immeasurable supplies of it1 while it is incompatible with whatever we seem to know about them to suppose that radium at any time entered into their composition4 ,the genesis of the elements has1 in truth1 not yet been made the subject of coherent speculation4 ,current ideas regarding it imply a double course of change1 by aggregation first1 and subsequently by disintegration4 ,and this should give us a twofold series of elements4 ,on one side there should be fixed survivals from the advancing process1 on the other1 products of decomposition1 continuously evolved1 and even now accumulating4 ,if the claim of helium to take rank among these last should be finally established1 our conceptions of the nature and history of nebul might have to undergo a strange inversion2 but the outcome of the researches in progress is still uncertain1 and may be far off4 ,it is1 nevertheless1 quite clear that the electronic theory of matter supplies no genuine explanation of the source of energy in the universe4 ,what is given out when the atoms go to pieces must have been stored up when they were put together4 ,whence was it derived8 ,this is the fundamental question which underlies every discussion concerning the maintenance of the life of suns4 ,it is unanswered1 and probably unanswerable4 ,,footnotes3 ,footnote #ajj3 ,it must at the same time be borne in mind that their total darkness is not proved4 ,all that is certain is that their spectra are not bright enough to leave any impression on the exposed plates4 ,footnote #aja3 ,thomson and ,tait1 ,natural ,philosophy1 ,appendix ,e1 p4 #did1 edition #ahij4 ,,chapter ,,xiv ,,our ,,own ,,system ,our sun is clearly middle-aged4 ,it bears none of the marks associated with juvenility in stars1 while its decrepitude is in the distant future4 ,it is crossing1 most likely1 a level tract where recuperation so nearly balances expenditure that radiation can be maintained for an indefinite time at a high and fairly uniform standard4 ,stars of the solar type pursue the even tenor of their way with particularly few interruptions4 ,they show little tendency to intrinsic variability4 ,their periodicity1 when it exists1 is due to the presence of a companion4 ,variables1 in other words1 belonging to the spectral family of our sun1 are binary systems2 and they are usually1 if not always1 non-eclipsing binaries1 on the pattern of ,cephei4 ,light changes can thus be impressed upon sunlike stars by external influence2 they do not conspicuously arise through native instability4 ,our planet1 accordingly1 is attached to a safe and steady luminary1 one subject1 not to destructive spasms1 but to vicissitudes so mild as to evade distinct meteorological recognition4#ajb ,it is1 moreover1 governed by a polity settled on a broad basis of tranquillity and permanence4 ,all this is as it should be4 ,the conditions specified were a pre-requisite to the unfolding of human destinies4 ,nor can it be confidently asserted that they have been realized anywhere else4 ,our system may be unique2 while1 on the other hand1 replicas of it might1 imperceptibly to us1 be profusely scattered through the wide realms of space4 ,it is certain that a telescopic observer on ,sirius or ,centauri would see our sun unattended2 not even ,jupiter could be brought into view by optical appliances in any degree comparable to those at our disposal4 ,there are1 nevertheless1 strict limitations to the possible diffusion of planetary worlds like those that wander amid the zodiacal constellations4 ,we have become aware of incapacitating circumstances1 by which a multitude of stars are precluded from maintaining retinues of subordinate globes4 ,spectroscopic discoveries have compelled a revision of ideas as to cosmical arrangements4 ,especially the large proportion established by them of binary to single stars makes it impossible any longer to regard the solar system as a pattern copied at large throughout the sidereal domain4 ,we cannot1 then1 compare it with any other2 the mechanism of which the earth forms part must1 perforce1 be studied in itself and by itself1 and it may1 for aught that appears1 be the outcome of special and peculiar design4 ,the machine in question is self-sustaining and self-regulating2 no extraneous power noticeably affects its working4 ,this immunity from disturbance is the fortunate consequence of its isolation4 ,a great void surrounds it4 ,the span of ,neptune's orbit is but a hand-breadth compared with the tremendous unoccupied gulf outside--unoccupied1 that is to say1 by bodies of substantial mass4 ,the feebleness of starlight relatively to sunlight affords some kind of measure of the impotence of stellar attractions to compete with the over-ruling gravitational power that sways the planetary circulation4 ,this it is which gives to it such remarkable stability4 ,the incomparable superiority of the sun over his dependent orbs not only safeguards them against foreign interference1 but reduces to insignificance their mutual perturbations4 ,hence the strong concentration of force exemplified in our system--the absolutely despotic nature of the authority exercised--makes for a settled order by excluding subversive change4 ,the organization of the solar kingdom1 as disclosed by modern research1 is greatly more varied and complex than ,laplace took it to be4 ,his genetic scheme was1 indeed1 no sooner promulgated than deviations from the regularity and unanimity of movement upon which it was based began to assert their inconvenient reality4 ,they have since multiplied2 and1 emerging to notice under the most unlikely aspects1 they occasion incongruities which tax1 for their explanation1 all the resources and audacities of the most inventive cosmogonists4 ,let us briefly consider their nature4 ,the swarm of asteroids that bridge the gap between ,mars and ,jupiter revolve1 it is true1 with the general swirl of planetary movement2 but they use a large license as regards the shape and lie of their orbits4 ,and their partial exemption from the rules of the road becomes entire for comets and meteors1 which have nevertheless proved themselves to be aboriginal in our system by their full participation in its proper motion4 ,finally1 several of the major planets set convention at defiance in the arrangement of their several households1 and thereby intimate departures from the supposed normal course of development so frequent and so considerable as to shake belief even in its qualified prevalence4 ,thus1 the anomalously short period of the inner satellite of ,mars1 besides throwing doubt over its own mode of origin1 tends to obscure the history of its more sedately circulating associate4 ,deimos cannot have been thrown off from its primary under conditions materially different from those attending the birth of ,phobos4 ,the sub-systems of ,uranus and ,neptune exhibit1 moreover1 eddies of retrograde movement suggesting primitive disturbances of a fundamental kind2 while the surprising disclosures connected with ,saturn's firstborn and furthest satellite1 photographically detected by ,professor ,w4 ,h4 ,pickering in #ahih1 have added one more knotted thread to the tangled skein we would fain unravel4 ,until acquaintance was made with ,phbe1 counterflows of revolution within the same satellite-family were unknown1 and1 if contemplated at all1 would have been scouted as impossible4 ,one ternary star1 to be sure-- ,scorpii--had been recognised as probably owning an immediate and a more remote attendant1 in oppositely directed orbital movement2#ajc but the cases are in many ways disparate1 and the analogy1 though instructive1 is imperfect4 ,if the ninth ,saturnian moon is to be regarded as sprung from the condensing mass of the planet1 a total change in the state of the parent body must have supervened during the long interval between its separation and that of its successor1 ,iapetus4 ,the change1 in ,professor ,w4 ,h4 ,pickering's opinion1#ajd was nothing less than a reversal of axial movement4 ,the nebulous spheroid destined to develop into the wonderful ,saturnian system had1 presumably1 when ,phbe became detached from it1 a diameter of sixteen million miles1 and gyrated tranquilly from east to west1 in a period of about a year and a half4 ,but the action of sun-raised tides availed first to destroy and finally to invert this movement2 for the natural outcome of tidal friction is synchronism1 and this implies agreement1 both in period and direction1 between the rotation and revolution of the body acted upon4 ,acceleration through contraction did the rest2 and by the time another satellite was ready to separate1 the originating globe span normally in seventy-nine days1 the actual revolutionary period of ,iapetus4 ,the view that such was the course of events is plausible at first sight2 yet the doubt remains whether the cause alleged was adequate to the effect produced4 ,at the distance of ,saturn1 solar tidal friction exerts only about #a_/bjjjj its power on the earth2#aje its efficacy would1 on the other hand1 be greatly enhanced by the distension of the mass subjected to it2 but approximately to what extent1 our powers of calculation are impotent to determine4 ,this is not all4 ,exhaustive photographic research promises to unfold intricacies of construction in secondary systems demanding the patient industry of many generations for their complete unravelment4 ,the families of the great planets will perhaps be found to include crowds of inferior members which pay slight heed in their circulatory arrangements to the trammels of convention4 ,in those of both ,jupiter and ,saturn the phenomenon has lately been brought to light of 'asteroidal' satellites1 as they may be termed1 minute bodies travelling round their primaries at nearly the same mean distances1 each group evidently representing the unagglomerated materials of a single full-sized satellite4 ,the pigmy components of such groups doubtless exist in multitudes2 each great planet1 most likely1 is encompassed by at least one zone of moonlets2 but so far only specimen-objects have been picked up4 ,the tenth ,saturnian satellite1 discovered1 like its predecessor1 by ,professor ,w4 ,h4 ,pickering1 is thus associated1 by its period and locality1 with ,hyperion1 the seventh and least prominent of ,saturn's visual train1 the apparent insignificance of which suggested to ,sir ,john ,herschel that it might have many co-occupants of the wide gap between ,titan and ,iapetus4#ajf ,but the surmise had to await verification until methods were intensified beyond what seemed possible in the middle of the nineteenth century4 ,the corresponding ,jovian pair found by ,professor ,perrine circulate far outside the boundaries of the original ,galilean realm1 in orbits which interlock as a consequence of their marked difference in eccentricity4#ajg ,they are mutually inclined at an angle of #bg degrees1 nor are they supposed actually to intersect1 so that collisions are apparently out of the question4 ,direct movement is indicated1 but cannot yet be claimed to belong quite certainly to both objects4 ,we are only beginning to make acquaintance with the submerged populations of the ,saturnian and ,jovian kingdoms2 they are perhaps multitudinous2 they are certainly peculiar1 and we await impatiently and curiously the further developments of their remarkable behaviour4 ,the one certain inference derivable from the diversity of facts ascertained within the last hundred years is that our world is not 7so to speak7 machine-made4 ,the modus operandi employed to disengage the planets from their nebulous matrix was not of cast-iron rigidity2 it was adaptable to circumstances2 it left room for the display of boundless inventiveness in details4 ,this was made1 nevertheless1 to consist with the perfect preservation of the main order1 both in design and operation4 ,the general plan is broadly laid down and unmistakable2 the springs of the machine are undisturbed in their free play1 and for the primary reason that departures from regularity1 which might1 in any way1 prove a menace to stability1 affect bodies of negligible mass4 ,the great swing of settled movement goes on irrespectively of them4 ',de minimis non curat lex4' ,so the erratic procedure of comets is harmless only because of their insignificance4 ,if imitated by substantially attractive masses1 it could not fail to jeopardize the planetary adjustments4 ,even the asteroids would be unsafe neighbours but for their impotence2 and it is remarkable that ,mercury1 by far the smallest of the major planets1 circulates along a track of the asteroidal type4 ,it would seem as if an important size carried with it an obligation to revolve in an orbit of small eccentricity1 inclined at a low angle to the principal plane of the system4 ,the reason why this should be so is not obvious2 but were it otherwise the equilibrium1 now so firmly established1 would subsist precariously1 or not at all4 ,the assertion1 indeed1 that it is firmly established can only be made under reserve4 ,we are ignorant of any causes tending towards its overthrow2 yet they may supervene1 or be already imperceptibly active4 ,one such lurking possibility is the presence of a resisting medium in interplanetary space4 ,waifs and strays of matter must1 beyond doubt1 be encountered there--outlawed molecules1 self expelled from the gaseous envelopes of feeble globes2 thin remnants of cometary paraphernalia1 driven off amid the fugitive splendours of perihelion2 products of ionic dissociation set flying by the impact of ultra-violet light--and all disseminated through an ethereal ocean1 which 'is cut away before and closes from behind' as moving bodies traverse it4 ,that its indifference is shared by ordinary material substances1 when in the last stage of attenuation1 is a plausible but unverified conjecture4 ,it is only safe to say that retardation of velocity in what may pass for empty space is insensible or null4 ,there may1 nevertheless1 be springs of decadence in the solar system4 ,some of them have been discussed by ,m4 ,poincar1#ajh whose confidence in the reassuring demonstrations of ,laplace and ,lagrange is inversely proportional to the magnitude of the terms they were forced to neglect4 ,they dealt with fictitious globes1 devoid of appreciable dimensions1 and swayed by the strict ,newtonian law4 ,but the real planets and their satellites are acted on by other forces as well1 frictional1 magnetic1 radio-repulsive1 the joint effects of which may not be wholly evanescent4 ,the tidal drag on rotation undoubtedly occasions a small but irretrievable loss of energy4 ,the moon1 for instance1 as ,m4 ,poincar states1 now gains1 by the reactive consequences of tidal friction in widening its orbit1 no more than #a_/bh the vis viva of which the earth is deprived by the infinitesimal slowing down of its rotation2 and the remaining #bg_/bh1 being dissipated abroad as heat1 are finally abstracted from the system4 ,the ultimate state1 we are told1 towards which the planetary mechanism tends is that of the synchronous revolution1 in a period of about twelve years1 of all its members4 ,this might1 apart from the possibility of a resisting medium1 have indefinite permanence2 otherwise precipitation to the centre would gradually ensue1 and one solitary sphere1 cold1 stark1 and unilluminated1 would replace the radiant orb of our cerulean skies1 with its diversified and exquisitely poised cortge4 ,unsecured drafts upon futurity1 however1 are not among the most valuable assets of science1 and a consummation so immeasurably remote may be anticipated by a score of unforeseen contingencies4 ,what can be and has been ascertained is the relative durability of the scheme with which the visible destinies of the human race are so closely connected4 ,it will unquestionably last long enough for their accomplishment4 ,curiosity that would seek to pierce the ulterior darkness is likely to remain ungratified4 ,but there is a further outlook4 ,other and incalculable items remain to be taken into account4 ,the sun1 although an autocrat within his own dominion1 is himself subject to external influences4 ,as a star1 he is compelled to follow whithersoever the combined attractions of his fellow-stars draw him2 nor can we thoroughly interpret the summons which he obeys4 ,the immediate upshot in the transport of the solar system towards the constellation ,lyra has1 it is true1 been determined1 but the eventual scope and purpose of the journey remain profoundly obscure4 ,the pace is to be reckoned as leisurely3 twelve miles a second is little more than half the average stellar speed4 ,we should1 however1 probably suffer no inconvenience from being whirled through the ether in the train of such a stellar thunderbolt as ,arcturus4 ,only the excessive velocities of any adventitious bodies we might happen to pick up would betray to ordinary experience the fact of our own swift progress4 ,as it is1 our sweepings from space appear to be scanty4 ,if shreds from inchoate worlds1 or dust of crumbled worlds1 strewed the path of our system1 they should be annexed by it in its passage1 temporarily or completely1 and we should then expect to find the apex of the sun's way marked1 if no otherwise1 by the predominant inflow from that quarter of comets and meteors4 ,yet there is no trace of such a preference in the distribution of their orbits4 ,hence the enforced conclusion that the sun has attached to him1 besides the members of his immediate household1 an indefinite crowd of distant retainers1 which1 by their attendance upon his march1 claim with him original corporate unity4 ,to this rule there may be a few exceptions4 ,an occasional aerolite probably enters the earth's atmosphere with hyperbolic velocity1 and takes rank accordingly as1 in the strictest sense1 a foreign intruder2 but the broad truth can scarcely be challenged that the sun travels through a virtual void4 ,we can1 however1 see no necessity why he should for ever continue to do so4 ,widely different conditions seem to prevail near the centre and out towards the circumference of the sidereal world4 ,what may be designated the interior vacuity of the ,milky ,way is occupied mainly by stars of the solar type1 including one to our apprehension super-eminent over the rest2 they are separated by vast1 apparently clear intervals2 they are non-nebulous1 and of stable constitution4 ,this secure habitat is ours for the present1 although it may at some future time be exchanged for one less exempt from disturbance4 ,the shape and size of the sun's orbit are utterly unknown2 the changes of environment1 accordingly1 that will accompany the description of it defy conjecture4 ,our actual course is inclined at a small angle to the plane of the ,milky ,way4 ,it will presumably become deflected1 but perhaps not sufficiently to keep our system clear of entanglement with the galactic star-throngs4 ,in our ignorance of their composition no forecast of the results can be attempted3 they are uncertain and exorbitantly remote4 ,moreover1 the comparative slowness of the sun's motion in a manner guarantees the permanence of his subsisting cosmical relations4 ,for anything that science can tell1 they may ultimately be subverted by some preordained catastrophe2 but the possibility lies outside the sphere of rational forecast4 ,the universe1 as reflected in the mind of man1 gains extent as the mirror acquires polish4 ,early astronomers conceived of but one solar system and one 'ddal earth1' upon which the 'pale populace of heaven' rained influences sinister or propitious4 ,later1 human egotism took another form4 ,the whole universe was assimilated to our particular little settlement in it4 ,terrestrial conditions were universalized4 ,none divergent from them were counted admissible or profitable4 ,but one answer seemed possible to the perpetual ,cui bono8 with which restless thought assailed the heavens4 ,but one purpose was regarded as worthy of fulfilment1 that of multiplying1 in distant sidereal climes1 copies of our own planet1 and of providing suitable locations for myriads of intellectual beings1 as little alien to ourselves as might be compatible with the minimum of diversity in their material surroundings4 ,the spread of this astral philanthropy has been in some measure checked by the advance of knowledge4 ,our position and circumstances have been shown by it to be1 if not quite peculiar1 at any rate very far from inevitable4 ,it has reduced1 by a process of exclusions1 to a relatively limited number the class of stars that can fairly be regarded as possible centres of vitality2 it has immensely widened the scope of discernible variety in cosmical arrangements1 and held out warnings against errors of exposition due to inborn prejudices4 ,and we shall surely not wander from the truth by recognising our inability to penetrate all the depths and complexities of ,infinite ,design4 ,,footnotes3 ,footnote #ajb3 ,the uncertainty affecting the best attainable results in weather-cycle investigation is rendered strikingly apparent by a comparison of the able and laborious papers by ,h4 ,w4 ,clough 7,astrophysical ,journal1 vol4 xxii41 p4 #db71 and ,c4 ,easton 7,petermann's ,geogr4 ,mittheilungen1 #aije1 ,heft ,,viii41 and ,proceedings ,amsterdam ,academy of ,sciences1 ,june #bd1 #aije74 ,footnote #ajc3 ,r4 ,t4 ,a4 ,innes1 ,reference ,catalogue1 p4 #aee;,a4 ,footnote #ajd3 ,harvard ,annals1 vol4 liii41 p4 #fa1 where1 however1 the reversal is explained by a shifting of the plane of rotation4 ,footnote #aje3 ,g4 ,h4 ,darwin1 ,philosophical ,transactions1 vol4 clxxii41 p4 #ebf2 ,moulton1 ,astrophysical ,journal1 vol4 xi41 p4 #aaj4 ,footnote #ajf3 ,monthly ,notices1 vol4 ix41 p4 #ia4 ,footnote #ajg3 ,f4 ,e4 ,ross1 ,lick ,bulletin1 ,no4 #hb4 ,footnote #ajh3 ,annuaire du ,bureau des ,longitudes1 #ahih4 ,,chapter ,,xv ,,remnants ,,and ,,survivals ,if the sun and planets were1 in sober truth1 wrought into their present shape out of a primordial nebula1 the comparatively void surrounding space should naturally be strewn with fragments of unappropriated material4 ,for the process of englobement could hardly1 one would think1 be carried out with such neatness and precision as to leave no shreds or shavings lying about the great atelier4 ,residual stuff there must be1 unless our preconceived ideas are grossly erroneous2 nor have we far to look in order to find it4 ,we find it1 apparently1 under two forms presenting curious dissimilarities1 yet belonging fundamentally1 we can scarcely doubt1 to the same order of things4 ,these two kinds of waste product may be identified in the innumerable army of comets and in the strange1 pale cone of the zodiacal light4 ,one of the most important and secure additions to knowledge in the department of cosmogony made during the nineteenth century was the establishment of comets in a position of entire1 perennial1 and aboriginal dependence upon the sun4 ,that is to say1 a vast majority1 if not the whole of them1 attend him on his sidereal journey4 ,they are1 accordingly1 and have immemorially been his clients1 and they can lose that status only through the effects of violent disturbance compelling them to depart irrevocably from their closed orbits along hyperbolic tracks4 ,a trifling leakage of comets from our system is thus possible1 which may or may not be compensated by annexations of adventitious members of the class1 similarly banished from the precincts of remote stars4 ,but this is a secondary consideration2 the essential point to be borne in mind is that comets are native-born subjects of the sun1 that they make an integral part of his cortge1 that they own the same substantial origin1 are dominated by his power1 and must share his fortunes4 ,their study should then prove strongly illuminative as to the pre-history of our system1 and for this especial reason1 that they seemingly belong by right to that vanished world which it is the chosen task of cosmogony to reconstruct4 ,they are1 we can infer1 the genuine primitives of the solar company2 they retain something of prairie wildness1 not having been broken in by steadily enforced gravitational discipline4 ,each perihelion passage is an adventure2 between it and the next1 fateful incidents may occur4 ,forces negligible on dense planetary globes act sensibly on their tenuous materials2 they in part strikingly illustrate1 and in part fantastically invert1 the common modes of natural procedure4 ,but it is their antiquarian significance that mainly concerns us here4 ,admitting for the inchoate solar nebula such a constitution as that devised by ,kant1 and adopted with amendments by ,m4 du ,ligonds1 we find ourselves confronted with the almost inevitable consequence of symptomatic survivals4 ,wisps of crude matter1 in other words1 which escaped being drawn into the vortices of embryo planets should continue to circulate1 as they had from the first circulated1 in all possible planes1 and with no partiality for either a right-handed or a left-handed direction4 ,these waifs and wastrels should1 in fact1 be indistinguishable from comets--'les seuls tmoins1' according to the ,french cosmogonist1 'qui nous restent sur le mode de la circulation premire4'#aji ,the identification is seductive to the imagination1 and does not fall far short of convincing the reason4 ,there is clear evidence that what we may venture to call the native mode of cometary circulation is absolutely exempt from the rules which impress the movements of the planets with an unequivocal stamp of congruity4 ,the few comets showing some degree of compliance with the general plan are those which have been subjected to manifold perturbations1 and can hence no longer be called as unbiassed witnesses2 while their untrained associates1 left relatively free to follow the impulsion of their start1 betray no geometrical preferences in their manner of travelling4 ,they revolve indifferently with or against the course of the signs2 their paths are inclined at every possible angle to the ecliptic2 they approach the sun in sensibly equal numbers from all quarters of the sky2 they agree only in pursuing ellipses so elongated as to verge towards the parabolic limit4 ,but just in this way1 and no otherwise1 we should expect to find bodies circulating which1 having been aggregated at random 7as ,kant supposed7 in the beginning1 had departed to the least possible extent from the initial conditions of their systemic union4 ,a good prim facie case can1 then1 be made out for regarding comets as samples of the used-up nebula1 as superannuated constituents of an inconceivable chaos1 which1 evading the operation of laws of change1 have floated down the stream of ages virtually intact and undisturbed4 ,yet the question has other aspects besides this purely mechanical one4 ,they should all be harmonized by truth1 which cannot be more securely guaranteed than by consilient testimony2 nevertheless1 there are difficulties in effecting the accommodation4 ,comets are not1 in a chemical sense1 closely related to nebul4 ,they are fundamentally of carbonaceous composition--free hydrogen makes no spectroscopic show in them--while they include metallic ingredients occasionally rendered glowing by the powerful excitement of a perihelion rush-past4 ,but gaseous nebul shine mainly with the light of certain unknown substances1 reinforced by rays of hydrogen and helium4 ,carbon flutings and metallic lines are alike alien to their spectra4 ,nor is there any community that we yet know of between the chemistry of white nebul and that of comets4 ,the nebular hypothesis of cometary origin is thus discountenanced by the results of light-analysis4 ,still1 there are possibilities of reconcilement4 ,spectral conditions must be subject to change4 ,the quality of light emitted by a body of mixed composition cannot fail to alter with the inevitable alteration of physical state brought about by external influences or internal change4 ,selective illumination is beyond doubt largely concerned in modifying the information we are able to obtain as to the composition of remote masses1 and its modes of action seem capricious because they are very imperfectly understood4 ,hence1 spectral modifications may take place merely through the substitution of some elements for others in carrying 7let us suppose7 an electric discharge1 though all were from the first simultaneously present in unvaried proportions4 ,moreover1 chemical immutability can no longer be taken for granted4 ,we have learned of late that even elementary individuality breaks down under the battering-ram of time4 ,sooner or later the stamp1 however apparently inviolable1 will be defaced1 transformations of species will ensue1 and novel combinations of material will subtly accommodate themselves to the needs of a growing world4 ,these things1 it is true1 are involved in much obscurity1 but we have caught glimpses of instability clear enough to convey an emphatic warning against dogmatic interpretations of spectral characters4 ,physical science may then license ,m4 du ,ligonds' theory of comets with a provisional ,nihil obstat4 ,the zodiacal light suggests a different set of considerations4 ,comets being of pre-planetary origin1 the ecliptical glow must be supposed post-planetary4 ,it belongs to a later epoch1 being composed1 according to an accepted opinion1#aaj of superfluous materials left over from the construction of the train of globes to which our own belongs4 ,it might be compared to whey from which the curd has been separated4 ,all the good has been got out of it2 we might be tempted to throw it aside upon the rising rubbish-heap of the skies1 with the importunate asteroidal throng1 a few dozen undistinguished comets1 and some hundreds of ill-defined meteoric systems4 ,but celestial refuse is always worth sifting1 above all1 for tokens of genealogical descent1 and we should be unwise to neglect the chance of finding them in the peculiar relations of the zodiacal light4 ,a triple phenomenon1 it consists1 when completely seen1 of a cone1 a band1 and a counterglow4 ,the connection of these parts into a whole is obvious1 though enigmatical4 ,usually1 however1 only the cone is visible4 ,it appears about the time of the spring and autumn equinoxes1 after sunset and before sunrise respectively1 as a faint lenticular illumination1 tapering upward from the sun's place below the horizon to an apex high up near the meridian4 ,under the name of the ',false ,dawn' it was familiar1 probably from an early age1 to ,oriental peoples4 ,but they looked for it at the opposite end of the night from that favoured by ,european observers2 nor did the phenomenon attract any particular notice here in ,england until #affj1 when ,joshua ,childrey published a description of it in his ,britannia ,baconica4 ,yet it had been specifically observed about seventy years previously by ,christoph ,rothmann of ,hesse1 and must have been less intelligently perceived by numberless spectators1 who most likely included it1 with such miscellaneous objects as comets' tails1 auroral beams1 and meteor-trails1 in the undefined class of appearances known from of old as trabes4 ,the light is ordinarily much feebler than the ,milky ,way1 which it nevertheless on occasions unmistakably outshines4#aaa ,real fluctuations of brightness seem implicated in these changes2 yet they follow no traceable law of periodicity1 and are certainly independent of the sunspot cycle4 ,the counterglow1 first remarked by ,peznas in #agcj1aab soon fell into oblivion1 and had to be rediscovered after six-score years by ,brorsen1 who bestowed upon it its current title of the ',gegenschein4' ,of late it has been pretty constantly observed1 particularly by ,professor ,barnard1 to whom it presented itself1 owing to the scantiness of the available records1 as a surprising novelty4#aac ,surprising it certainly is4 ,the appearance of the ,gegenschein is that of a large elliptical patch of diffuse light1 measuring about #ab by #i degrees1 and situated diametrically opposite to the sun4#aad ,now and again1 though somewhat rarely1 it is perceived to be united to the cone by the 'zodiacal band1' a strip of evanescent luminosity nearly following the line of the ecliptic4 ,we cannot1 then1 be mistaken in recognising the great pyramidal beam centred on the sun1 with the counterglow and its linking band1 as sections of a single formation1 constituting in a manner the substratum of the solar system4 ,a recent observation made by ,professor ,newcomb under unique conditions proves it to be much less exclusively 'zodiacal' than had been supposed4 ,looking north from the summit of the ,rothhorn1 at midnight1 on ,july #bi1 #aije1 he perceived a well-marked glow spreading #ce degrees from the sun's place4#aae ,it was the light in its thwartwise aspect1 which had never before been seen1 or even looked for2 and we learn from it the remarkable fact that the sun is enclosed in a vast1 dimly luminous sphere1 with a girth not much smaller than the orbit of ,venus1 and indefinitely diffused along the equatorial plane4 ,notwithstanding its dim indefiniteness1 neither the spectroscope nor the camera is wholly ineffective for the scrutiny of this extraordinary appurtenance4 ,we have learned positively that its radiance is of the continuous sort1 the origin of which through the reflection of sunlight from small solid bodies seems more than probable4 ,the whole structure must accordingly be of a pulverulent or meteoric nature2 it consists of independently moving particles4 ,but to the further question1 ,under what regimen do these particles circulate8 no decisive answer is as yet forthcoming4 ,m4 ,hansky#aaf and others hold the light to be a true solar appendage1 an extension of the corona1 in which case it would have a formal1 but no material permanence4 ,it would represent the continually changing aggregate of multitudinous minute bodies issuing from or repelled by the sun1 and in large proportion falling back towards his surface4 ,yet some difficulty is raised to this view by the vast dimensions of the problematical glow4 ,that it extends far beyond the earth's orbit is rendered patent by the phenomena of the ,gegenschein and the band4 ,true1 the scope of the sun's repulsive action cannot be limited2 still1 we might naturally expect its products to become too attenuated for recognition beyond a radius of perhaps fifty million miles4 ,admitting1 on the other hand1 the residual character of the zodiacal light1 we should attribute to it a constitution analogous to that of ,saturn's rings4 ,each one of the cosmic atoms collected in it would revolve round the sun on its own account1 scarcely disturbed by its neighbours4 ,nor need we despair of determining with reasonable certainty which way the truth lies in this matter4 ,the rival hypotheses may be tried by a criterion the application of which is by no means remotely feasible4 ,it is furnished by the geometrical relations of the zodiacal light4 ,evidently1 if the sun can claim organic connection with it1 its axis should coincide with the plane of the solar equator2 while1 if it represent wastage from the ,kantian nebula1 it should stretch along the principal plane of our system--the plane of maximum moment of momentum--the plane towards which the primitive agglomeration of revolving particles collapsed as it condensed4 ,the question of planes is1 then1 crucial4 ,is the zodiacal effluence placed symmetrically as regards the solar equator1 or does it appertain properly to the ecliptic1 which deviates very slightly from the fundamental plane of the solar system8 ,the evidence is1 unfortunately1 contradictory4 ,most observers have located the dim equinoctial cone right along the pathway of the sun2 some1 under exceptionally favourable circumstances1 have perceived in it a marked departure from the track of the ,signs4 ,m4 ,marchand's determinations from the ,pic du ,midi1 for instance1 indicated a probable coincidence between the solar equatorial plane and the axis of the light2#aag and ,dr4 ,max ,wolf succeeded1 in #ahhi1 in getting a photographic impression which1 though partial and imperfect1 tended to corroborate ,marchand's inference4#aah ,again1 on ,november #af1 #aijd1 when the cone showed a remarkable lustre1 it was distinctly perceived at ,knigstuhl to sheer off and separate from the ecliptic as it mounted the sky4 ,now1 however1 that a beginning has been made in photographing this enigmatical tenant of the sphere 7the feat has been performed at ,flagstaff as well as at ,heidelberg71 we may confidently expect a speedy reconcilement of inconsistent statements regarding its whereabouts4 ,until then we cannot venture to assert that it is in actual reality what it appears to be1 a nebulous survival4 ,,footnotes3 ,footnote #aji3 ,ligonds1 quoted by l',abb ,moreux1 ,le ,problme ,solaire1 p4 #fg4 ,footnote #aaj3 ,moreux1 ,le ,problme ,solaire1 p4 #acc2 ,ledger1 ,nineteenth ,century1 ,march1 #aije4 ,footnote #aaa3 ,humboldt1 ,cosmos1 vol4 iv41 p4 #efc 7,ott's translation72 ,maunder1 ,journal of the ,british ,astronomical ,association1 vol4 viii41 p4 #agd2 ,max ,wolf1 ,knigstuhl ,report for #aijd4 ,footnote #aab3 ,paris ,memoirs1 #agca1 quoted by ,r4 ,wolf1 ,geschichte der ,astronomie1 p4 #fie4 ,footnote #aac3 ,popular ,astronomy1 vol4 i41 p4 #ccg4 ,footnote #aad3 ,nijland1 ,astr4 ,nach41 ,no4 #d1jjh4 ,footnote #aae3 ,astrophysical ,journal1 vol4 xxii41 p4 #bji4 ,footnote #aaf3 ,comptes ,rendus1 #aije1 ,no4 #f2 ,nature1 ,february #bc1 #aije4 ,footnote #aag3 ,comptes ,rendus1 tom4 cxxi41 p4 #aacd4 ,footnote #aah3 ,sitzungsberichte1 ,munich1 ,bd4 ,,xxx41 p4 #aig4 ,,chapter ,,xvi ,,life ,,as ,,the ,,outcome ,the making of worlds1 we are assured1 was not purposeless1 and its most obvious purpose to our minds is the preparation of suitable abodes for organic life4 ,no other seems of comparable importance2 no other1 indeed1 comes within the full grasp of our apprehensive intelligence4 ,yet its limitations must not be forgotten4 ,the human standpoint is not the only one from which the sum of things may be surveyed2 and although we be unable to quit it1 we can still admit that the view obtainable from it is probably not all-embracing4 ,we only know with certainty that the end which appears to us supreme has1 in one case1 been successfully attained2 how far it was sought to be compassed elsewhere must always remain a matter of speculation4 ,on our own globe the presence of life is none the less mysterious for being profuse and familiar4 ,we can trace the strange history of its slow unfolding1 but the secret of its initiation baffles our utmost scrutiny4 ,the cooled rind of a once molten globe serves as the stage for the drama2 beneath it primeval heat still reigns4 ,temperature rises steadily with descent into the interior of the earth2 at a depth of about two miles it must reach the boiling-point of water at the sea-level4 ,this temperature1 which is absolutely prohibitive of vitality1 was formerly1 beyond question1 that of the surface4 ,at some long past epoch1 accordingly1 our future oceans hung suspended as a prodigious envelope of vapour above a hot crust of slag and lava2 our teeming planet lay barren2 it harboured no promise1 no potency1 no visible possibility of life4 ,so it should have remained had the law of continuity been rigidly enforced2 but there came a time for a new beginning1 and a new beginning was made4 ,a momentous alteration took place2 inert ,nature was quickened2 what had been sterile became all at once fruitful2 an immeasurable gulf was bridged1 and movement was started along an endless line of advance4 ,that the advance was set on foot and directed by an intelligent ,will is the only inference derivable from a rational survey of the known facts4 ,life can be studied in its manifestations1 not in itself4 ,attempts to define it have served only to show our inability to 'lift the painted veil4' ,we can1 however1 see that its presence is attended by characteristic effects1 brought about in harmony with the laws of inorganic nature1 although not in blind submission to them4 ,their operation is somehow restrained1 and appears to be subtly though securely guided towards determinate ends prescribed by the vital needs of each animal or plant4 ,this modifying principle unmistakably regulates the economy of every living organism2 the cessation of its activity means death4 ,science has made no real progress towards solving the enigma of vitality4 ,its evasiveness becomes1 on the contrary1 more apparent as inquiry is rendered more exact4 ,under a laxer discipline of thought the contrast between life and death seemed less glaring4 ,it was easily taken for granted that creeping things were engendered by corruption1 aid being invoked1 if required1 from the virtus clestis of the eighth sphere4 ,thus1 the birth of mice from the damp earth was1 in the ninth century1 held to be signified by the word mus 7humus72#aai and ,van ,helmont1 at the height of the revival of learning1 published without misgiving a recipe for the creation of the same animals4#abj ,yet there was already better knowledge to be had for the asking2 and ,francesco ,redi1 in #affh1 crystallized ,harvey's opinion in the celebrated maxim1 ',omne vivum ex vivo4' ,its truth is incontrovertible4 ,challenged and tested again and again1 it has as often been vindicated1 and may now be said1 despite certain anomalous effects of radium on veal broth1 to stand outside the legitimate range of debate4 ',that life is an antecedent to life1' ,lord ,kelvin declared in #ahga1 'seems to me as sure a teaching of science as the law of gravitation4'#aba ,but the succession is not easy to start within the terms of a strictly uniformitarian convention4 ,the expedient is tempting1 if scarcely satisfactory1 of demanding from the past what we dare not claim from the present4 ,two and a half millenniums ago it was already in vogue4 ,herodotus dismisses a genealogical embarrassment with the remark1 ' 1 which may be freely translated1 ',in the long run of time anything may happen4' ,conditions1 we are apt to think1 may have been more elastic long ago4 ,the proven impossibility of to-day becomes vaguely thinkable seen through the mist of uncounted yesterdays4 ',if it were given to me1' ,professor ,huxley said1#abb 'to look beyond the abyss of geologically recorded time to the still more remote period when the earth was passing through physical and chemical conditions which it can no more see again than a man can recall his infancy1 ,i should expect to be a witness of the evolution of living protoplasm from non-living matter4' ,to these first vital compounds he attributed a fungoid nature and mode of growth1 and the choice deprived his speculation of any plausibility that might otherwise have belonged to it4 ,fungi are not self-supporting2 they cannot supply themselves with nourishment from the raw materials of the mineral world2 they depend upon the hospitality of differently organized beings4 ,they were1 then1 certainly not among the 'first mercies of nature4' ,mr4 ,herbert ,spencer1 too1 was inclined to regard spontaneous generation as a superannuated process4 ,the leap from the non-vital to the vital1 now admitted by the saner kind of biologists to be impracticable1 might have been taken1 it seemed to him1 when 'the heat of the earth's surface was falling through those ranges of temperature at which the higher organic compounds are unstable4' ,but the 'reason why' is to seek4 ,a sterilized solution is precisely one which has cooled from a high thermal grade2 a baked brick is similarly circumstanced4 ,why should the appearance of life in primeval times have been favoured by a state of things fatal to it here and now8 ,the essence of the biological crux resides in 'protoplasm4' ,the word was coined by ,von ,mohl in #ahdf1 with the object of emphasizing the importance of the substance it signified1 which indeed forms the bulk of every organism1 animal and vegetable1 man1 mushroom1 and amba4 ,huxley rightly termed it 'the physical basis of life1' adding1 however1 the infelicitous conjecture that its production might have been one of the lucky hits of nature4 ,it would have been a hit of incalculable moment1 but of incalculable improbability4 ',odds beyond arithmetic' were against that particular throw coming out of the ,lucretian dice-box4 ,the 'primal slime' 7to use ,oken's phrase7 is composed of oxygen1 nitrogen1 hydrogen1 and carbon1 with minute percentages of phosphates and other salts4 ,but these constituents are put together in a highly artificial manner4 ,eight or nine hundred elementary atoms1 in fact1 go to the making of one molecule of protoplasm1 forming a structure of extreme complexity1 most delicately balanced and eminently unstable4 ,it results1 accordingly1 from the employment of specially directed forces1 and stores1 for the benefit of the producing organism1 the energy expended in its construction4 ,left to itself1 it promptly goes to pieces1 and yields back its component particles to their native inorganic sphere4 ,the laws there ruling are in truth adverse to the existence of protoplasm2 abandoned to their unmitigated action1 it perishes4 ,we should then as reasonably suppose that in the geological past rivers flowed uphill as that inorganic nature stumbled blindly upon this wonderful postulate and product of life4 ,professor ,huxley affirmed life to be 'a property of protoplasm1' the inevitable outcome of 'the nature and disposition of its molecules1' and he sought to cover the absurdity of the dictum by claiming as analogous a case wholly disparate4 ,water1 he argued1 has qualities totally unlike those of oxygen or hydrogen1 and protoplasm may similarly1 by mere intricacy of arrangement1 and the evoking of latent affinities1 become endowed with the transcendant powers connected with animated existence4 ',what better philosophical status1 then1' he exclaimed1 'has vitality than aquosity8'#abc ',true1' he added1 'protoplasm can only be generated by protoplasm1 in a manner that evades our intelligence1 but does anybody quite comprehend the modus operandi of an electric spark which traverses a mixture of oxygen and hydrogen8' ,the illustration is inapt4 ,the electric spark fulfils no constructive function4 ,it simply agitates the molecules so as to bring their native affinities into play4 ,it acts like a mechanical blow on dynamite4 ,further1 water is a stable compound1 because its formation is attended by loss of energy2 it represents a plane permanently occupied because reached by a steep descent2 but protoplasm is1 in this respect1 the antitype of water4 ,it needs force for its composition2 water needs force for its decomposition4 ,protoplasm needs force plus a suitable apparatus2 it can be turned out only by an artfully adapted machine with a head of steam on4 ,it is thus continually manufactured by plants under the stimulus of light4 ,they provide the apparatus1 sunbeams the energy4 ,if the supply of power is cut off1 the machinery comes to a halt1 protoplasm ceases to be generated1 the organism dies of inanition4 ,many ,german biologists find themselves compelled1 by the impossibility of explaining vital activities in terms of chemistry or physics1 to associate protoplasm with some kind of psychical activity4#abd ,individuality1 at least1 implies an ultra-material principle1 and it asserts itself at the very base of the animal creation4 ,an amba is the simplest of living beings4 ,formerly called the ',proteus animalcule1' it is 'everything in turn1 and nothing long4' ,it can be round or radiated1 spherical or lenticular1 as momentary convenience prescribes4 ,organs it has none1 its limbs are conspicuous by absence1 it is 'sans everything' that belongs to the ordinary outfit of an animated creature4 ,yet such-like nucleated globules of protoplasm have flourished exuberantly during countless ages4 ,adaptability insured survival4 ,an amba is at home in almost any environment4 ,what it has not ready-made1 it can supply at a moment's notice4 ,out of any part of its substance it can improvise feelers and tentacles for the capture of its prey1 as well as a stomach for its digestion1 and it thus effectively goes through the full round of animal economy4 ,some varieties1 too1 are noted builders4 ,those called ,foraminifera have the faculty of secreting carbonate of lime from sea-water1 and construct with it fairy dwellings1 perforated in all directions to allow of the protrusion of exploratory filaments4 ,fossil chambered shells of this type are extraordinarily abundant4 ,their dense conglomeration in the chalk elicited ,buffon's exclamation that 'the very dust had been alive6'#abe ,the calcaire grossier of which ,paris is built consists mainly of them1 and to this day1 in oceanic depths1 the materials of future capitals are in course of preparation by the monumental industry of these unpretending creatures4 ,such as they are1 they maintain a status incomparable with that of non-living things4 ,incomparable1 for instance1 as regards the water in which they float4 ,the contrast is startling despite its familiarity4 ,an amba incarnates a purpose2 it embodies a spark of personal existence1 unconsciously swaying the forces of inorganic nature towards the ends of its own well-being4 ,the subordination is most real1 though profoundly mysterious4 ,in the organic and the inorganic worlds the same laws hold good2 the same ultimate atoms exert their preferences in each2 in neither is an uncaused effect possible4 ,a bullet can no more be fired from a gun that has no charge than a man can lift a finger without a corresponding outlay of food-products4 ,accordingly1 while plants store and animals expend energy1 plants and animals are equally incompetent for its origination4 ,what they can do is to appropriate and specifically apply it2 and herein resides the essence of life4 ',it would seem1' ,sir ,george ,stokes wrote in #ahic1abf 'to be something of the nature of a directing power1 not counteracting the action of the physical forces1 but guiding them into a determined channel4' ,what the power is in itself it would be futile to seek to define4 ,we are only sure of its being extra-physical4 ,matter cannot evolve a principle which disposes of it as its master4 ,evolution means only the unfolding into self-evidence of something already obscurely present4 ,the 'latent process' 7to use a ,baconian term7 of the hatching of an egg is typical and instructive4 ,yet it is not the less recondite for being daily conducted before our eyes4 ,a concourse of suns1 indeed1 fails to impress us with the unutterable wonder of the 'flower in the crannied wall' apostrophized by the last great poet of the nineteenth century4 ,the two wide kingdoms of life lack a 'scientific frontier4' ,the boundary-line is ill-marked and irregular4 ,so much so that a few naturalists have set up a neutral zone1 or no man's land1 inhabited by creatures of mixed or uncertain nature1 by plant-animals1 or zoophytes in the literal sense of the word4 ,but the expedient avails to shelter ignorance rather than to advance knowledge4 ,for it seems probable that there is no organism so imperfectly characterized as to be genuinely incapable of giving a categorical answer to the question1 ',under which king1 ,bezonian8' ,fungi might1 perhaps1 on a superficial view1 be taken for hybrids4 ,they share the nature of animals so far as to be unable to elaborate their own food1 while appearing in other respects to be authentic vegetables4 ,they are1 in fact1 parasites and scavengers4 ,not the smallest reason exists for supposing them to constitute a genetic link between the two chief hierarchies4 ,these are1 in all likelihood1 fundamentally distinct4 ,only by a gratuitous hypothesis can they be credited with a common ancestor4 ,each seeks a different kind of perfection2 their ideals1 so to speak1 follow divergent tracks4 ,that the tracks were marked out from the beginning may be safely affirmed2 and this implies radical separation4 ,plants came first1 since animals pre-suppose and imperatively require them2 the antecedence having quite possibly been by a vast interval of time4 ,on this point1 geological evidence1 though inconclusive1 is suggestive4 ,the ,laurentian beds1 which are among the very earliest stratified formations1 contain no recognisable fossils4 ,they were once supposed to enshrine the remains of a lowly organism dubbed ,eozon ,canadense2 but the markings that simulated animal forms are now known to be of mineral origin4 ,laurentian graphite1 on the other hand1 occurs plentifully2 and graphite may be described as coal at a more advanced stage of mineralization4 ,such deposits1 we are led to believe1 consist of altered vegetable substances2 and it seems to follow that these hoary rocks are the burying ground of a profuse succession of virgin forests4 ,that they flourished beneath the sea--were1 in fact1 composed of alg--was the opinion of ,professor ,prestwich1#abg and it is not easily gainsaid4 ,primitive animal life was unquestionably marine1 and the ,huronian strata1 which overlie the ,laurentian1 afford traces of it in a few sponge-spicules1 the cast of an annelid1 and such-like scanty leavings4 ,higher up1 the ,cambrian series swarms with oceanic invertebrates2 fishes1 the first type of vertebrates1 came upon the scene in ,silurian times2 and so1 by a various and surprising progression1 life advanced through the ages1 until the ascending sequence culminated with a being cast in a diviner mould1 who walks the earth1 even now1 with face uplifted to the stars4 ',natus homo est2 illum mundi melioris origo ,finxit in effigiem moderantm cuncta deorum4' ,in the vegetable kingdom the vital law of development has wrought with less conspicuous effect4 ,the superiority of recent to ancient floras is more significant than striking4 ,a tree-fern or a sigillaria bears comparison with an oak much better than a trilobite or a plesiosaurus with an eagle1 horse1 or lion4 ,the geological variations of plants1 however1 have unmistakably tended to make them more serviceable to man--more serviceable to his material needs1 and also more gratifying to his sthetic instincts4 ,for him1 flower-petals were painted and perfumes distilled2 for him1 the grasses of the prairie laid up stores of sustaining nutriment2 in preparation for his advent1 choice fruits ripened and reddened under ,tertiary sunshine2 while the barren and sombre vegetation of the ,carboniferous epoch had already done its part by dying down into seams of coal for the eventual supply of power for human industry and warmth for human comfort4 ,it would be an abuse of our readers' patience to discuss the futile conjecture of an extra-terrestrial origin for life on our globe4 ,the agency1 in this connection1 of germ-laden aerolites was first invoked by ,richter of ,dresden2 and ,lord ,kelvin gave currency to the notion by an incidental reference to it in #ahga from the ,presidential ,chair of the ,british ,association4 ,its adoption would oblige us to regard the denizens of our planet1 fauna and flora alike1 as salvage from the wreck of some unknown world in space4 ,credat ,judus ,apella4 ,to our minds1 the adventures of ,baron ,munchausen appear more credible than the pre-natal history of the primal organism implied by this 'wild surmise4' ,inquiry into the nature of the supposed organism serves to draw closer the web of embarrassment4 ,the remarkable aridity of meteorites excludes the possibility of its having had an aquatic habitat4 ,members of the fungoid order are unsuited to act as pioneers1 owing to their helplessness in the matter of commissariat2 and the spores or lichens or mosses could scarcely be expected to survive the vicissitudes of such a journey as they must have performed if meteor-borne to terrestrial shores4 ,the immigration hypothesis1 moreover1 even if it were plausible1 could not be made useful4 ,difficulties do not vanish on being pushed into a corner2 the problem of life is as formidable in one world as in another2 we should not expect to find it easier to square the circle in ,mars than ,deinostratos found it in ,greece2 matter1 we are convinced1 has no more psychical initiative in the system of ,arcturus than can be ascribed to it in the system of the sun4 ,profitless conjectures may then be dismissed2 they do not help us out of the slough of intellectual impotence4 ,this need not1 indeed1 be absolute4 ,the determination to regard things mechanically alone renders them unintelligible4 ,science becomes unscientific when it refuses to be guided by experience2 and we have the plainest testimony of consciousness to the working in ourselves of originative faculties independent of1 and irrepressible by1 physical agencies4 ,here we hold the clue to the labyrinth4 ,the intimation conveyed is distinct of a ,power outside nature1 continually and inscrutably acting for order1 elevation1 and vivification4 ,,footnotes3 ,footnote #aai3 ,hewitt1 ,problems of the ,age1 p4 #aje4 ,footnote #abj3 ,pasteur1 ,annales de ,chimie et de ,physique1 tome xliv41 p4 #f1 #ahfb4 ,footnote #aba3 ,popular ,lectures and ,addresses1 vol4 ii41 p4 #aih4 ,footnote #abb3 ,report ,british ,association1 #ahgj1 p4 #hd4 ,footnote #abc3 ,collected ,essays1 vol4 i41 p4 #aec ,footnote #abd3 ,neumeister1 ,betrachtungen ber das ,wesen der ,lebenserscheinungen1 #aijc4 ,footnote #abe3 ,owen1 ,palontology1 pp4 #aa1 #ad4 ,footnote #abf3 ,gifford ,lectures1 p4 #df4 ,footnote #abg3 ,geology1 vol4 ii41 p4 #bb4 ,,index ,alexander1 structure of the ,milky ,way1 #bad ,amba1 versatile organization1 #bgd-e ,anaximander1 generalized matter1 #e ,anaximenes1 air as the ',urstoff1' #d1 #aea ,aristotle1 conception of nature1 #h2 solid spheres1 #ac ,asteroids1 orbital relations1 #bcf ,babinet1 objection to ,laplace's cosmogony1 #dd ,bacon1 elemental triad1 #aea ,ball1 ,sir ,robert1 mechanics of a condensing nebula1 #gi1 #bji-aj ,barnard1 discoveries of nebul1 #bab2 observations of the ,gegenschein1 #bei ,becquerel1 detection of radio-activity1 #aeg1 #afb ,bessel1 astronomy of the invisible1 #ada ,bode's law of planetary distances1 #bf ,brorsen1 the zodiacal counterglow1 #bei ,bruno1 a platonic pantheist1 #i ,buffon1 cometary impacts1 #fa2 fossil foraminifera1 #bge ,campbell1 system of ,geminorum1 #aac2 number of spectroscopic binaries1 #adc2 density of nebulium1 #aec ,chladni1 meteoric cosmogony1 #aah ,comets1 position in ,cartesian system1 #ab-ac2 in that of ,laplace1 #acf2 origin1 #gc-d1 #beb-d2 meteoric relations1 #abb-d1 #acc2 solar dependants1 #acc1 #adj1 #bcf1 #bea2 nebular affinities1 #acg1 #bed-e2 insignificant mass1 #bdb ,cosmogony1 primitive1 #a-c1 #ad2 philosophical1 #c-g2 scientific1 #g1 #ae2 of ,descartes1 #aa-ac1 #fj2 ,kant's1 #ba-bh1 #fa-b1 #beb1 #bed2 ,laplace's1 #bi-cc1 #ch-ec1 #eg-fa1 #ach1 #bce2 ,herschel's1 #ce-g1 #acf1 #aii-bja2 ,faye's1 #fh-gf1 #ha1 #abi2 ,lockyer's1 #abe-acd2 sidereal1 #aje-g1 #ade-g1 #bag-bcj ,crookes1 ,sir ,william1 protyle1 #e1 #adi2 radiant matter1 #aed1 #aef-g2 future of the world1 #afc ,curie1 ,madame1 discovery of radium1 #afb ,dalton1 combining equivalents1 #aeb ,dark stars1 #ada1 #bbf-g ,darwin1 condensation of nebulous rings1 #db1 #ea2 history of earth-moon system1 #hg-ib1 #id1 #ig1 #adb2 equilibrium of rotating globes1 #ajb1 #ajd-e1 #aab1 #adc2 fluid pressure on meteor-swarms1 #abi1 #aca2 spiral nebul1 #bje ,delambre1 on cosmic speculations1 #ad1 #ae ,democritus1 mechanical theory of the world1 #e1 #bb ,descartes1 theory of vortices1 #aa-ac ,dissipation of energy1 #bbi ,double stars1 genesis and development1 #ih-i1 #ajf-g1 #adb-e1 #bbf-g2 occulting1 #ajh-aac2 variable1 #aac-aae1 #adc2 'dumb-bell' type1 #aae1 #aaf1 #adc2 frequency of occurrence1 #add1 #bcd ,earth1 effective rigidity1 #hf2 critical situation1 #hg2 antique disruption1 #hi1 #ia2 tidal effects upon1 #ij1 #bdd2 meteoric intakes1 #aai-abj1 #acc2 internal heat1 #bff ,easton1 the galactic spiral1 #bad ,eclipses1 stellar1 #ajg-h2 questionable occurrence1 #aji-aac2 criterion of reality1 #aad ,electricity1 discharge through vacua1 #aed2 relations with disintegrated matter1 #aee1 #aei-afj1 #afc2 gravity explained by1 #agg-h1 #agi2 dual properties1 #ahj-aha2 fundamental in nature1 #ahb2 ethereal transmission1 #ahe ,electrons1 copious production1 #agd2 strain-centres1 #ahi-aij1 #aie2 ultimates of matter1 #bca ,elements1 ancient and medival ideas regarding1 #e1 #aea2 genesis1 #aeb1 #bcj-bca ,empedocles1 four elements1 #e1 #aea ,ether1 in ,cartesian philosophy1 #ab2 evasive character1 #aei1 #ahc1 #aig-h2 relation to gravity1 #age1 #ahe2 properties1 #ahd1 #aia1 #aic-d ,evolution1 of solar system1 #bb1 #bda1 #bej2 of stars1 #ce-f1 #bag-bbe2 of stellar systems1 #ih-i1 #ajf-g1 #adb-e1 #bbf-g2 of nebul1 #ade-f1 #bjj-baa2 of the chemical elements1 #aea1 #bcj-bca ,faye1 objections to ,laplace's cosmogony1 #be2 modified scheme1 #fh-gc1 #ha1 #abi2 duration of the sun1 #gf ,fleming1 nature of electrons1 #aie ,frost and ,adams1 spectroscopic binaries1 #adc1 #bba ,galileo1 first law of motion1 #ab ,goldstein1 cathode-rays1 #aee ,gravitation1 mode of action1 #afh1 #ahe2 velocity of transmission1 #afi1 #age1 #agg2 explanatory hypotheses1 #agj-agi ,hale1 relationships of carbon stars1 #bbe ,halley1 nature of nebul1 #cf ,hansky1 status of zodiacal light1 #bfa ,harvey1 life from life1 #bfh ,helium1 present in the sun1 #ee2 origin by atomic decay1 #aeh1 #bcj2 absorption in stars1 #bbj1 #bbb-c2 a constituent of nebul1 #bcj ,helmholtz1 maintenance of solar heat1 #ca1 #cd1 #ce1 #gd-e ,helmont1 spontaneous generation1 #bfh ,heracleitus1 elemental evolution1 #aea ,herodotus1 omnipotence of time1 #bfi ,herschel1 ,sir ,john1 nature of atoms1 #aef2 ,saturn's satellites1 #bdj ,herschel1 ,sir ,william1 ,uranian system1 #bi2 sidereal evolution1 #ce-f1 #cg1 #acf2 observations of nebul1 #aii2 history of their growth1 #bjj-bja ,huggins1 ,sir ,william1 discovery of gaseous nebul1 #ed1 #aec ,huggins1 ,sir ,william and ,lady1 stellar development1 #bbf ,huxley1 origin of life1 #bfi1 #bga1 #bgb ,hydrogen1 molecular velocity1 #ee2 the unit-atom1 #aeb2 tenuity1 #aec2 absorption in stars1 #bba-b ,island-universes1 #ed ,jeans1 figures of equilibrium1 #ajd-e2 nature of radio-activity1 #aif ,jupiter's system1 #bdj-a ,kant1 cosmological speculations1 #bj-bh1 #fj-fb1 #beb1 #bed2 tidal effects1 #bg1 #hd-e2 ,saturn's rings1 #di2 status of comets1 #gc ,kelvin1 ,lord1 ,lesage's theory of gravitation1 #agd2 vortex-atoms1 #ahg2 dissipation of energy1 #bbi2 origin of life1 #bfh1 #bhj ,kepler1 physical astronomy1 #aj ,kirkwood1 objection to nebular hypothesis1 #ej1 #ea2 effects of solar tidal friction1 #fg ,lambert1 sidereal construction1 #ag-ah ,langley1 mass of meteoric infalls1 #aai ,laplace1 hypothesis of planetary origin1 #be1 #bi-ca1 #cc1 #cf-db1 #eb-c1 #eh-i1 #fj-fb1 #bce2 ,saturn's ring-system1 #di2 ,mcanique ,cleste1 #eg2 status of comets1 #gc1 #acf ,larmor1 scheme of molecular physics1 #ahh2 definition of ether1 #ahi1 #aic ,lenard1 cathode-rays1 #aeg ,lesage1 rationale of gravity1 #agb-c1 #age ,lewis1 masses of double stars1 #bbf ,ligonds1 scheme of planetary growth1 #gg-h1 #ha1 #beb2 comets as survivals1 #bec1 #bef ,lockyer1 ,sir ,norman1 meteoritic hypothesis1 #abe-g2 enhanced lines1 #bbc ,lorentz1 electrical hypothesis of gravity1 #agg-h1 #ahe ,magellanic clouds1 spiral conformation1 #bac ,marchand1 plane of the zodiacal light1 #bfc ,mars1 rotation of1 #dg-h ,maxwell1 origin of matter1 #afa2 corpuscular theory of gravitation1 #agc ,mayer1 ,j4 ,r41 effects of tidal friction1 #hg ,mercury1 action upon of solar tides1 #hh1 #if2 eccentric orbit1 #bdb ,meteoritic formation of planets1 #bh-i1 #aai-abb1 #abe1 #abh1 #aca-c2 of comets1 #abb-d2 of nebul1 #abf-g1 #acd ,meteors1 abundance1 #aai1 #acc2 mineralogy1 #aba-b1 #acd2 hyperbolic orbits1 #acc2 attendance on the sun1 #bcf ,meteor-swarms1 progressive dispersal1 #gb1 #abd2 constitution1 #abb-d1 #abh-aca2 primitive existence1 #acd ,milky ,way1 theories regarding1 #af-ag1 #bae2 undeveloped condition1 #bja1 #bjg2 relation to sun's movement1 #bdg ,mohl1 protoplasm1 #bgj ,moment of momentum1 #bc1 #dj1 #dd1 #de1 #fe1 #bji ,moon1 origin1 #hg-ib1 #ig1 #aci1 #ade2 retreat from the earth1 #bdd ,moulton1 nebular cosmogony1 #dd1 #ea1 #hb ,myers1 systems of ,lyr and ,u ,pegasi1 #aji-aaj ,nebul1 gaseous composition1 #cg1 #aec1 #bja1 #bje2 illusory resolution1 #ec2 spiral structure1 #gi-hj1 #ajf1 #adf1 #aij1 #bjd-bjh1 #baa-bad2 classification1 #aii2 development1 #bjj-bjb1 #bje1 #bjg-baa2 relation to stars1 #bjb-c1 #bje2 helium ingredient1 #bcj1 #bee ,nebular hypothesis1 propounded by ,kant1 #bb-h2 by ,laplace1 #bi-ca1 #ch1 #eb-c1 #fa2 difficulties1 #ci-eb1 #ed-f2 amendments1 #fj-hb ,nebulium1 a constituent of nebul1 #ed1 #aec1 #bja ,neptune1 retrograde system of1 #dc1 #eb1 #bcg ,newcomb1 transverse observation of the zodiacal light1 #bfj ,newton1 transmission of gravity1 #ahd1 #ahe ,nova ,persei1 nebulous appurtenance1 #bjf ,perrine1 new ,jovian satellites1 #bdj ,peznas1 notice of the counterglow1 #bei ,phobos1 anomalous revolution1 #dg-h1 #bcg ,phbe1 retrograde motion1 #if1 #bcg-h ,pickering1 ,e4 ,c41 binary nature of ,v ,puppis1 #aab2 structural relations of the ,looped ,nebula1 #bac ,pickering1 ,w4 ,h41 origin of ,phbe1 #ig1 #bch2 photograph of a great nebula1 #bab2 satellite discoveries1 #bcg1 #bdj ,plato1 conception of a world-soul1 #h ,poincar1 rotational equilibrium1 #aja1 #aje1 #aaj1 #adc2 destiny of the solar system1 #bdc-d ,prestwich1 ,laurentian graphite1 #bgi ,proctor1 structure of the ,milky ,way1 #bad ,protoplasm1 its properties1 #bgj-bgc ,protyle1 supposed discovery1 #adi1 #aed-g2 function and qualities1 #aeb2 cosmic relations1 #afd-e ,prout1 unity of matter1 #aeb ,radio-activity1 possible effects1 #cc-d1 #bbi2 discovery1 #aeg2 nature and cause1 #aeh-i1 #afb-c1 #aif ,red stars1 affinities1 #bbd-f ,redi1 transmission of life1 #bfh ,reynolds1 explanation of gravity1 #agj2 molecular physics1 #ahh1 #aib-c ,richter1 germ-laden aerolites1 #bhj ,roberts1 ,a4 ,w41 systems of ,r#b ,centauri and of ,v ,puppis1 #aaa1 #aac ,roberts1 ,isaac1 spiral arrangements of stars1 #bad ,roche1 planet-making expedients1 #dh2 reconstruction of ,laplace's hypothesis1 #fb-fg ,roche's limit1 #fc1 #aae-f ,rntgen rays1 discovery1 #aeg2 ethereal nature1 #aeh1 #agf2 electronic effects1 #afc2 suggested connection with gravity1 #agf ,rothmann1 early notice of the zodiacal light1 #bef ,russell1 photographs of ,magellanic ,clouds1 #bac ,rutherford1 atomic disintegration1 #afb ,satellites1 periods of revolution1 #df2 anomalies of movement1 #dg-h1 #eb1 #if1 #bcf-i2 effects on of tidal friction1 #ic-d1 #if1 #ig1 #bch2 origin by fission1 #aje2 'asteroidal1' #bci-dj ,saturnian system1 an example to cosmogonists1 #da1 #ga2 anomalies1 #di1 #eb1 #if1 #bcg-bdj ,schaeberle1 photographs of nebulous spirals1 #bjd1 #bab ,secchi1 star-classification1 #bai ,see1 tidal friction in stellar systems1 #ih1 #adb ,shelley's ,demiorgon1 #i ,solar system1 origin1 #bb1 #ci-db1 #fi-hb1 #bda2 anomalies1 #bi1 #dc-eb1 #bcf-bda2 mechanism1 #cj1 #bcd-e2 stability1 #bce1 #bdb2 springs of decadence1 #bdc-e2 translation1 #bde-h ,spectroscopic binaries1 #ih1 #aab-aad1 #adb-d1 #bba ,spencer1 status of nebul1 #ed2 spontaneous generation1 #bgj ,spinoza1 pantheistic views1 #i ,stars1 relations to nebul1 #ce-f1 #bjb-c2 distribution1 #adg2 relative ages1 #bag-bba1 #bbe2 spectra1 #bba-e ,stokes1 ,sir ,george1 nature of life1 #bgf ,stoney1 criticism of gravitational hypothesis1 #agi ,sun1 mode of development1 #be1 #ca2 maintenance of heat1 #ca-e2 helium-constituent1 #ee-f2 stellar relationships1 #bbd-e2 actual standing1 #bcb-c2 motion in space1 #bde-h ,swedenborg1 cosmic evolution1 #d1 #f1 #ae ,thales1 ideas of cosmic evolution1 #d1 #ad1 #aea ,thomson1 ,j4 ,j41 mass of corpuscles1 #aeh2 gravitational effects1 #agc2 ,rntgen rays and gravity1 #agf2 ether and matter1 #aij ,tidal friction1 effects in earth-moon system1 #bh1 #hg-ib1 #id1 #ig1 #bdd2 in other sub-systems1 #dh1 #ej1 #ic-g1 #bch-i2 on binary stars1 #ih-i1 #ajh1 #adb2 modifying power1 #df-g1 #fg-h1 #hc-g ,tisserand1 transmission-rate of gravity1 #age ,uranian system1 retrograde motion1 #dc1 #eb1 #gj1 #bcg ,variable stars1 #ajh-aae ,venus1 mode of rotation1 #if ,vogel1 stellar development1 #bai1 #bbe ,whewell1 status of nebul1 #ed ,whittaker1 undulatory theory of gravity1 #agh-i ,wilson1 radium in the sun1 #cd ,wolf1 ,c41 motion of ,phobos1 #dh2 solar tidal friction1 #fg2 criticism of ,faye's cosmogony1 #gc ,wolf1 ,max1 photographs of the zodiacal light1 #bfc ,world ,soul1 function in cosmogony1 #h-i ,wright1 theory of the ,milky ,way1 #af-ag1 #ah1 #bj ,zodiacal light1 origin1 #bef-g1 #bfa1 #bfd2 triple aspect1 #beg-fj2 transversal dimensions1 #bfj2 constitution1 #bfb2 plane of extension1 #bfb-c ,,billing ,,and ,,sons1 ,,ltd41 ,,printers1 ,,guildford