FOOTNOTES:

FOOTNOTES:[45]The New Astronomy, p. 197.[46]American Journal of Science, vol. xi., p. 421, June, 1901.[47]Carbon does not liquefy under ordinary conditions. In the production of his artificial diamonds M. Moissan employed tremendous pressure and great heat; and, although the genuineness of his products has been denied (Combes,Moniteur Scientifique, November, 1903), his methods at least seem to have approximated to those by which Nature fabricates her most authentic crystals.[48]Sir R. Ball,The Earth's Beginnings, p. 243.[49]Proceedings of the Royal Society, vol. xlv., p. 4.

[45]The New Astronomy, p. 197.

[46]American Journal of Science, vol. xi., p. 421, June, 1901.

[47]Carbon does not liquefy under ordinary conditions. In the production of his artificial diamonds M. Moissan employed tremendous pressure and great heat; and, although the genuineness of his products has been denied (Combes,Moniteur Scientifique, November, 1903), his methods at least seem to have approximated to those by which Nature fabricates her most authentic crystals.

[48]Sir R. Ball,The Earth's Beginnings, p. 243.

[49]Proceedings of the Royal Society, vol. xlv., p. 4.

COSMOGONY IN THE TWENTIETH CENTURY

Prospectiveand retrospective inquiries into physical conditions stand very much on the same footing. The same degree of uncertainty attaches to results of both kinds; the same qualifications need to be applied to them; a similar reserve is understood to accompany our admission of them. The reserve grows more marked as science unfolds to our surprised apprehension the multiplex possibilities of Nature. The time has gone by when 'men of light and leading' could draw cheques for unlimited amounts on the bank of public credulity. Not that the balance has diminished, but that it is reserved for other uses. Most of us in these days, have learnt to 'look before and after' for ourselves, and we instinctively mix the proverbial grain of salt with what istold to us, even on the highest authority. Ideas are on the move; dim vistas are opening out; much that lies beyond the verge of actual experience is seen to be possible, and sedate reasoning may at any moment suffer outrage by fantastic discovery. Hence, finality of assertion is out of date.

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 origin. They have become more subtle, more far-reaching, yet less confident. They have ramified in unexpected directions, but rather tentatively, than with the full assurance of attaining absolute truth. Laplace considered only the solar system, from which he arbitrarily excluded comets. On the vast sidereal world he bestowed barely casual attention. Sir William Herschel, on the other hand, occupied himself exclusively with the growth-processes of nebulæ, relegating the details of planetary evolution to a position of secondary importance. Later, the spectroscope having become available for discriminating generic differences among the suns in space, their relative ages, the order of their succession,their mutual affinities, claimed predominant attention. Just now, however, the flood of speculation is too high to be restrained within separate channels; cosmogonists look far afield; they aim at obtaining a general survey of relations bewildering in their complexity. To some extent they have succeeded; parts are beginning to find their places in a great whole; links are seen to connect phenomena at first sight seemingly isolated; on all sides analogies are springing into view. The unwearied circling of the moon and its imperturbable face remind us how a sun may have been born; the flash of every meteor suggests the mode by which suns die. The filmy traceries of comets intimate the nature of the force acting in nebulæ; the great cosmic law of spirality is remotely hinted at by the antipodal disturbances of the sun. Thus, one set of facts dovetails into the next; none can be properly considered apart from the rest.

The limitations of the human mind impose, nevertheless, restrictions of treatment. Individual efforts cannot grapple with the whole of the known and the knowable, and the larger part of both is included in the scope ofmodern cosmogony. It deals with all that the skies hold, visibly or invisibly; draws unstintingly on time past and time to come; concerns itself equally with gradual transformations and sudden catastrophes, with the dissipation and concentration of energy, with the subtle interplay of matter and force, with physical and ultra-physical, chemical and electrical modes of action. But let us consider a little more particularly how things actually stand, so as to collect some definite ideas regarding the lines of advance practicable and promising for the immediate future.

To begin with our domestic circle. 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 theory. Much light has thereby been thrown upon planetary pre-history. The relations of planets to the sun, and of satellites to planets, have been rendered comparatively intelligible. Noticeable above all is the discovery thence ensuing of the earth's suggestive position, just outside the boundary of the region where planetary rotation wasdestroyed by sun-raised tides, and with it the prospects of planetary vitality.

Moreover, the dubious state of the inchoate terrestrial spheroid, consequent upon its intermediate situation, accounts for the peculiar mode of birth of the moon, and the distinctively binary character of the earth-moon system; while the variety perceptible in the circumstances of the different planets precludes the employment of any single recipe for their development from a primal vortex. The forces concerned, we can now see, acted in a far more complex manner than could formerly have been supposed, and their balance was proportionately more delicate. To which side it would have inclined in a given case must then often be incalculable, or calculable only with the guidance of the known result. The strict bonds of reasoning have thus become somewhat relaxed, and difficulties that looked formidable have, in the long run, proved not to be insuperable. But conviction has also grown faint. The old, imposing façade of theory remains erect; the building behind it has been, for the most part, pulled to pieces, and the architect has yet to be foundwho can reconstruct it to our satisfaction.

On one point we have, nevertheless, acquired certainty. It is now known that comets with their dependent trains of meteors are aboriginal in the solar system. They are no unlicensed intruders, but collateral relations of the planetary family. Possibly they represent waste scraps of world-stuff which escaped the action of the formative machinery; and if so, they exemplify its primitive texture. Not that their composition need be, on this supposition, identical with that of the planets. A sifting of elements would have been likely to accompany the processes of cooling and contraction. Comets were, perhaps, made (to speak illustratively) of the white of the nebulous egg, planets of its yolk. 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-spreading, fleecy haze, flung aside before 'the starry tides' had as yet begun to 'set towards the centre.' In one respect the quality of these relics is a surprise. They show no chemical affinity with nebulæ. Theirspectra are radically different from nebular spectra, gaseous or continuous. They accordingly lend no countenance, although not fatally adverse to the view that the sun was once, in the distinctive sense, a nebulous star.

The grand topic of sidereal succession is no longer abandoned to fruitless surmises. Broad lines have been laid down, along which, so far as we can at present see, progress must inevitably have been conducted. And one fact of overwhelming significance in this connection is entirely of recent discovery. The multitudinous existence of obscure bodies in space had, indeed, been foreseen as a logical necessity long before Bessel founded the 'Astronomy of the Invisible'; but its strong substantiation is almost wholly due to the use of modern spectrographic methods. Decrepit or dusky suns are assuredly no imaginary product, but a potent reality, though it would be too much to assert that all have sunk to extinction by the same road. Nor is it absolutely certain that their present state is uniformly the outcome of prolonged decay. Circumstances connected with many of themsuggest rather a congenital incapacity for shining.

We stand, too, on firmer ground than our predecessors in respect to the history of stellar systems. That its course is mainly prescribed by the influence of tidal friction has been ably demonstrated by Dr. See. Telescopic double stars can be led back by the aid of this clue to an initial stage, when they revolved close together, very much like the earth and moon in Professor Darwin's theory; and it was owing to their voluminousness and the unequal attractions it engendered that their orbits became enlarged and elongated to the degree generally observed.

This theoretical inference has been confirmed with singular aptness by the discovery of spectroscopic binaries. Pairs circling in orbits too narrow for visual discernment are the natural complement of pairs just divisible with the telescope; the first class represent the unseen, early stages of the second. The two together form an unbroken sequence of stellar systems, for spectroscopic binaries include couples fully separated, and still separating, as well as others barely divided, and revolving almost in contact. Nay, they include specimens, we are led to believe, of globes conjoined into the apioidal figure theoretically investigated by Darwin and Poincaré, which may be regarded as preparatory to the development by fission of two mutually revolving stars from one primitive rotating mass. Some of these supposed dumb-bell systems are variable in light; and if the eclipse-rationale of their obscurations be confirmed by the spectroscope, there is no gainsaying the inference that each flickering object is composed of two stars actually contiguous, if not confluent.

Now, compound stars are by no means of exceptional occurrence. Their relative abundance has been found to augment rapidly with every advance in our knowledge of the heavens. From the measures of stellar radial velocity lately carried out at the Yerkes Observatory by Professors Frost and Adams, it appears that the proportion of binary to single stars considerably exceeds Professor Campbell's earlier estimate. If those giving helium-spectra are alone considered, there are most probably as many of one kind as of the other. But why the distinction? it may be asked.The answer is not far to seek. Helium stars are the most primitive, and form the closest and most readily apparent systems. The companions of more fully developed stars would be likely to give less striking spectroscopic signs of their presence. A physically double star must always remain such. There is no law of divorce by which it can put away its companion, although their relations must alter with time. But their alteration tends continually to enhance the difficulty of their detection. For as the members of a pair are pushed asunder by tidal friction their velocity slackens, and the tell-tale swing of their spectral lines diminishes in amplitude, and finally, by its minuteness, evades observation.

And since the majority of spectroscopic satellite-stars are very imperfectly luminous, their eventual telescopic discovery, when far enough away from their primaries to be optically separable from them, would rarely ensue. It must then be concluded that half the stars in the heavens (let us say) broke up into two or more bodies as they condensed. What follows? Well, this. Half the stars in the heavens were, from the first, incapacitatedfrom becoming the centres of planetary systems. To our apprehension, at least, it appears obvious that a binary condition must have inhibited the operations of planetary growth. These innumerable systems are doubtless organized on a totally different principle from that regulating the family of the sun. The nebular hypothesis, even in its most improved form, has no application to them; the meteoritic hypothesis still less. Mathematical theories of fluid equilibrium, combined with a long series of changes due to tidal friction, afford some degree of insight into the mode of their origin and the course of their development. Yet the analogy with the earth-moon couple, which irresistibly suggests itself, is imperfect, and may be misleading, owing to the wide difference in state between plastic globes approaching solidification, and sunlike bodies radiating intensely and probably gaseous to the core.[50]

The world of nebulæ confronts us with entire cycles of evolutionary problems, which can no longer be treated in the offhand manner perforce adopted by Herschel. The objects inquestion are of bewildering variety; yet we can trace, amid their fantastic irregularities, the underlying uniformity of one constructive thought. Nearly all show, more or less markedly, a spiral conformation, and a spiral conformation intimates the action of known or discoverable laws. Their investigation must, indeed, be slow and toilsome; its progress may long be impeded by the interposition of novel questions, both in physics and mechanics; nevertheless, the lines prescribed for it seem definite enough to give hope of its leading finally to a clear issue. And when at last something has been fairly well ascertained regarding the past and future of nebulous spirals, no contemptible inroad will have been made on the stupendous enigma of sidereal relationships.

Its aspect, if we venture to look at it in its entirety, is vast and formidable. Not now, as in former times, with a mere fragment of creation—a single star and its puny client-globes, one of which happens to be the temporary abode of the human race—but with the undivided, abysmal cosmos, the science of origin and destiny concerns itself. The obscureand immeasurable uncertainties of galactic history invite or compel attention. We know just enough to whet our desire to know a great deal more. The distribution of stars and nebulæ is easily seen to be the outcome of design. By what means, we cannot but ask ourselves, was the design executed? How were things ordered when those means began to be employed? How will they be ordered when all is done? For an ultimate condition has, presumably, not yet been reached. And if not, agencies must be at work for the perfecting of the supreme purpose, which are not, perhaps, too subtle for our apprehension. Meanwhile, facts bearing on sidereal construction are being diligently collected and sifted, and we shall do well to suspend speculation until their larger import is made known.

The inquisitions of science do not cease here. They strive to penetrate a deeper mystery than that of the scattering in space of stars and nebulæ. What are they made of? is the further question that presents itself. What is the nature of the primal world-stuff? Whence did it obtain heat? By what meanswas motion imparted to it? If it be urged that such-like topics elude the grasp of finite intelligence and belong to the secrets of creative power, we may reply that we are not entitled, nor are we able, to draw an arbitrary line, not to be transgressed by our vagrant thoughts. The world has been, by express decree, thrown wide to their excursions, and it is not for us to restrict their freedom. We need not fear getting too near the heart of the mystery; there is no terminus in the unknown to which we can travel by express; in a sense, we are always starting, and never get nearer to our destination. But that is because it retreats before us. We do, in truth, advance; and as we advance the mists clear, and we see glimpses beyond of imperishable order, of impenetrable splendour. Our inquiries need not then be abandoned in despair at the far-reaching character they have spontaneously assumed.

From the earliest times there has been a tendency to regard varieties of matter as derivative. They have been supposed to be procured by supramundane agency, or by the operation of inherent law, from some universalundifferentiated substance. We moderns call that substance 'protyle,'[51]and believe ourselves to be in experimental touch with it. The implications of this view we shall consider in the next chapter.

FOOTNOTES:[50]Cf.Jeans,Astrophysical Journal, vol. xxii., p. 93.[51]A term signifying 'first matter,' constructed from corresponding Greek words by Roger Bacon, and revived by Sir William Crookes.

[50]Cf.Jeans,Astrophysical Journal, vol. xxii., p. 93.

[51]A term signifying 'first matter,' constructed from corresponding Greek words by Roger Bacon, and revived by Sir William Crookes.

PROTYLE: WHAT IS IT?

Thenotion of a primordial form of matter meets us at every stage of cosmogonical speculation. It is the outcome of an instinctive persuasion that, if we could only 'lift the painted veil' of phenomena, the real business of the universe would be found to be proceeding in the background, 'without haste or rest,' on a settled plan everywhere the same; that uniformity is fundamental, diversity only incidental; and that the transformations of the one simplified substance might be represented by a single formula, the discovery of which would place in our hands the master-key to the locked secrets of the universe. Among untutored thinkers some familiar kind of matter, idealized and generalized, commonly stood for the typical world-stuff. Water wasthe first favourite. Thales, the 'wise man' of Miletus, procured his cosmos by precipitation from an aqueous solution, and many savage tribes have devised analogous expedients. Anaximenes regarded air as the universal solvent; Heracleitus replaced it with fire, and set on foot a scheme of what is now often designated 'elemental evolution.' From the perpetual 'flux of things' he conceived that the four substances selected by Empedocles as the bases of nature were not exempt, and a fragment of his scheme survived in Francis Bacon's admission of the mutual convertibility of air and water. In the main, however, the author of the 'Novum Organum' adhered to the Paracelsian doctrine of an elemental triad,[52]although he regarded the association of salt as a fundamental 'principle' with sulphur and mercury as inept and unnecessary.[53]

These twilight fancies faded in the growing light of chemical science; yet the mental need that they had temporarily appeased survived,and had somehow to be satisfied. An 'Ur-Stoff' was still in demand, but the nineteenth century characteristically attempted to supply it by weight and measure. Dalton's combining equivalents afforded the warrant for Prout's hydrogen hypothesis. 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 formed. The condition indispensable to be fulfilled was that their weights should be exact multiples of that of the unit, and it came near to fulfilment by the hydrogen-atom or semi-atom. It was, nevertheless, a case in which approximate agreement was of no avail; the adverse decision of the balance finally became unmistakable; and Prout discreetly fell back, in 1831,[54]upon the expedient of deriving hydrogen itself from some body lower in the scale. His hypothesis, in short, dissolved into a conjecture. 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 things, but likewise as the substratum of all the chemical species.

Meanwhile, the theoretical search for it had been carried on in widely different fields of inquiry. Laplace's speculations, no less than Herschel's observations, had led to the conception of some kind of 'fire-mist' as the genuine star-plasm. But its nature and properties remained indefinite, or were assigned at the arbitrary choice of adventurous cosmogonists. So the 'shining fluid' of space was 'everything by turns and nothing long,' until Sir William Huggins, in 1864, gave it spectroscopic individuality. The 'recognition-mark' of nebulium is a vivid green ray, by the emission of which it is known to have a concrete existence. Yet the little that has besides been learned about it discountenances its identification with themateria informisof antique philosophy. This we should expect to be the subtlest of all substances. Professor Campbell, however, has gathered indications that nebulium is denser than hydrogen. Its luminosity, at least, which is invariably associated with that of hydrogen, spreads less widely in the same formations; it is confined to a lower level. The nebulium-atom is not, then, the chemical or the cosmical unit.

This evasive entity, or something that curiously simulates it, has proved to be of less recondite origin. 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 ago. The discovery was astonishing and unsought, and its significance has not yet been measured. Matter assumes the 'fourth state,' in which it is neither solid, liquid, nor gaseous,[55]under the compulsion of an electric discharge in high vacua. At an exhaustion of about one-millionth of an atmosphere the manner of its transit abruptly alters. Conduction gives way to convection. Luminous effects are abolished. The tubes cease to glow with brilliant, parti-coloured striæ; the poles are no longer marked by shimmering halos or brushes; only a green phosphorescence is seen where the glass walls of the receptacle are struck by the stream of projected particles. They come, with half the velocity of light, exclusively from the negative pole, the positive pole remaining inert. Hence the name'cathode-rays,' bestowed by Goldstein on the carriers of electricity in highly-exhausted bulbs.

These mysterious, sub-sensible agents possess certain very definite properties. Their paths are deflected in a magnetic field; they can traverse metallic films; and their investigation in the open, thereby rendered feasible, has shown them to possess photographic efficacy, and the faculty of breaking down electrical insulation; moreover, they transport a negative charge of fixed amount, and have a determinate momentum. They are, then, assuredly no mere pulsations of the ether; unless our senses 'both fail and deceive us,' their quality is material. Material, yet not quite with the ordinary connotation of the term. The most essential circumstance about the cathode-rays is that they remain unmodified by the chemical diversities of the originating gases.[56]A hydrogen tube yields identically the same radiant matter as an oxygen or a nitrogen tube. Here, then, at last we havewithin our grasp undifferentiated substance—matter not yet specialized, neither molecular nor atomic, matter destitute of affinities, exempt from the laws of combination—matter in its inchoate, and perhaps ultimate form; in a word, the far-sought protyle.

Already, in 1879, Sir William Crookes conjectured the infinitesimal missiles propelled from the cathode to be the 'foundation-stones of which atoms are composed.'[57]And in 1886 he pronounced them more decisively to be the raw material of atoms, which, to Sir John Herschel's apprehension, bore the unmistakable stamp of a 'manufactured article.' Nor did his recent commentator refrain from attempting distantly to divine the method of their construction, or from laying his finger on the by-products and residues associated with it,[58]although he felt compelled to relegate the cosmic factory to the edge of the world, where inconceivable things may happen. All this, indeed, seemed, in the late Victorian era, like mounting the horse of Astolfo for a trip to themoon; and sane common-sense pronounced it fantastic enough to 'make Democritus weep and Heracleitus laugh.'[59]But we have since learned from Nature herself some tolerance of audacities.

Step by step the new order of ideas has irresistibly come to the front. It owed its origin to Sir William Crookes's skill in producing high vacua, and the consequent development in his tubes of radiant effects. Then, in 1879, universal importance was claimed for them, and matter in the 'fourth state,' by a revival of the dreams of the ancients, expanded into a kind of visionary protyle. Philipp Lenard made the next advance towards its actualization by slipping it, in 1894, through an aluminium window, and watching its behaviour towards ordinary matter. Two years later Röntgen rays made their entry on the scene; and before the end of 1896 Becquerel, hurrying along the track of novelties, came upon the momentous discovery of radio-activity.

A revision of ideas has ensued. Some time-honoured assumptions have had to be discarded; so-called laws have been found toneed qualification; the old system of physics is consequently out of gear, and much time and patient labour must be expended upon the adjustment of the new and improved system destined to replace it. 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 nature. All are of a 'radiant' character. They travel in straight lines with enormous speed; they start from a material base, and produce their several effects on reaching a material goal. Now, these effects are closely alike, notwithstanding that the rays themselves are radically dissimilar. Those of the cathodic kind are corpuscular. They consist of streaming particles, each, according to Professor J. J. Thomson, of about one-thousandth the mass of the hydrogen atom. Others, the noted 'alpha rays,' are atomic; they are supposed to aggregate into helium. Finally, the Röntgen variety are ethereal; they are composed of light-vibrations reduced in scale, and augmented correspondingly in frequency.

What is most remarkable is that thesevarious forms of activity give rise, by different means, to very much the same results. They are, in fact, distinguishable only by careful observation. They possess in common, though not to the same degree, the faculties of penetrating opaque matter, of impressing sensitive plates, of evoking fluorescence; while under the impact of cathode and Röntgen rays, as well as of ultra-violet light, insulated electric charges leak away and evanesce. There is, however, one clear note of separation between cathodic and X rays in the sensibility of the former, and the indifference of the latter, to magnetic influence. Thus alone, it would appear, is electrified matter set apart from what we call ether. A magnet acts only upon bodies carrying an electric charge; so that, if flying corpuscles could be obtained in a neutral condition, the only tangible distinction between the various kinds of rays would vanish. But this is evidently impracticable. Indeed, advanced physicists abolish the material substratum of the corpuscle, and assign its attributes to the associated atom of electricity. It is, at any rate, undeniable that the electrical relations of matter become moreintimate as our analysis of its constitution goes deeper. Ether, electricity, matter, all seem to merge together in the limit; their differences ultimately evade definition. So animal and vegetable life appear to coalesce in their incipient stages, and strike apart with advance towards a higher perfection.

The various branches of inorganic nature, too, possibly spring from a common stock. Our powers of discrimination fail to separate them as we trace them downward; but that may be because of the inadequacy of the guiding principles at our command. A larger synthesis is demanded for the harmonizing of multitudinous facts, at present grouped incongruously, or left in baffling isolation; and it is rendered increasingly difficult of attainment by the continual growth of specialization. Year by year details accumulate, and the strain of keeping them under mental command becomes heavier; yet whatcanbe knownmust, in its essentials, be known as a preliminary to extending the reign of recognised law in Nature.

Sooner or later, nevertheless, the wealth of novel experience recently acquired will doubtless be turned to the fullest account. Just now,we can grasp only tentatively its far-reaching import. That it bears profoundly on the hoary problem of the genesis of visible things is sufficiently obvious. The questions of what matter is, and of how it came to be, have been cleared of some of the metaphysical cobwebs involving themab antiquo, and insistently crave definite treatment by exact methods. We should, indeed, vainly aspire to reach—or to comprehend, even if we could reach—an absolute beginning. To quote Clerk Maxwell's words: 'Science,'[60]he wrote, 'is incompetent to reason upon the creation of matter itself out of nothing. We have reached the utmost limit of our thinking faculties when we have admitted that, because matter cannot be eternal and self-existent, it must have been created.' The discovery that atoms disintegrate into corpuscles does not, then, bring us any nearer to the heart of the mystery; but it is eminently suggestive as regards secondary processes.

Acquaintance with ultra-atomic matter, begun within the narrow precincts of 'Crookes's tubes,' has advanced rapidly since 'radiology' took its place among the sciences. For, fromthe time when Becquerel first saw a plate darkened by the photogenic projectiles of uranium, and Madame Curie sifted radium from the refuse of the mines of Joachimsthal, the lines of proof steadily converged towards the conclusion that chemical atoms are not only divisible, but that their decay progresses spontaneously, irresistibly, in fire, air, earth, and water, as part of the regular economy of Nature.

To explain further. Radio-active bodies are composed—according to Rutherford's plausible hypothesis—of atoms in unstable equilibrium. The gradual changes incidental to their own internal activities suffice to bring about their disruption. And their explosive character is obviously connected with unwieldy size, since uranium, thorium, and radium, the three substances pre-eminent for radio-activity, possess the highest atomic weights known to chemistry. The precarious balance, then, of each of these complex, though infinitesimally small systems is successively overthrown, regardless of external conditions or environment, their constituent parts being hurled abroad with the evolution of an almost incredible amount of energy. Their products include cathode-rays;matter in the 'fourth state,' matter a thousand times finer than hydrogen, is ejected in torrents from the self-pulverized atoms of radium. Moreover, the issuing rays are equivalent to currents of negative electricity. Each corpuscle bears with it an electron, or is itself an electron, for the choice between the alternatives is open. In either case, we are confronted with matter apparently in its ultimate form; and to that form ordinary, substantial bodies tend to become reduced. Electrons may fairly be called ubiquitous. They occur in flames, near all very hot masses, wherever ultra-violet light impinges on a metallic surface;[61]they are freely generated by Röntgen and cathode-rays; they are the agents of electrical transmission in conductors.

Everywhere throughout the universe, atoms are thus in course of degradation into corpuscles. But no information is at hand as to the scene or mode of their reconstitution. The waste and decay are patent; the processes of compensation remain buried in obscurity. Indeed, Sir William Crookes anticipates thecomplete submergence, at some indefinitely remote epoch, of material substance in protyle, the 'formless mist' of chaos. He assumes an identity between the past state and the future, leaving, however, the present unexplained. The break-up of matter, in fact, does not render its construction the more intelligible. Running-down is an operation of a different order from winding-up. It is an expenditure of a reserve of force. It needs no effort; it accomplishes itself. But to create the reserve for expenditure demands foresight and deliberate exertion; it implies a designed application of power.

Now each atom is a storehouse of energy, representing the force primitively applied to reduce some thousands of free electrons to the bondage of a harmoniously working system. Its disruption is accompanied by the dissipation of the energy previously accumulated in it; and that atomic systems are not calculated for indefinite endurance is one of the most surprising of modern discoveries. The secret of their original construction is, none the less, impenetrable. That they are composed of protyle—that their clustering members are corpuscles moving under strong mechanicalcontrol—is more than probable. 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 fortuitous. But beyond this point there is no holding-ground for distinct thought. We are ignorant, too, whether the process of building matter out of protyle is at present going on, or was completed once for all in the abysmal fore-time, decay being now definitive. Nor is it likely that we shall ever succeed in capturing with recognition a brand-new atom freshly minted for cosmical circulation.

FOOTNOTES:[52]First introduced by Basilius Valentinus. See Fowler's edition of theNovum Organum, p. 576, note.[53]Thus recurring, as Mr. Fowler remarked (loc. cit.), to Geber's earlier view.[54]Dictionary of National Biography, vol. xlvi., p. 426.[55]Crookes,Philosophical Transactions, vol. clxx., p. 163.[56]J. J. Thomson,The Discharge of Electricity through Gases, p. 195;Philosophical Magazine, vol. xliv., p. 311.[57]Science, June 26, 1903.[58]Proceedings of the Chemical Society, March 2, 1888.[59]Times, March 30, 1888.[60]Encyclopædia Britannica, article 'Atom.'[61]Fleming,Proceedings Royal Institution, vol. xvii., p. 169.

[52]First introduced by Basilius Valentinus. See Fowler's edition of theNovum Organum, p. 576, note.

[53]Thus recurring, as Mr. Fowler remarked (loc. cit.), to Geber's earlier view.

[54]Dictionary of National Biography, vol. xlvi., p. 426.

[55]Crookes,Philosophical Transactions, vol. clxx., p. 163.

[56]J. J. Thomson,The Discharge of Electricity through Gases, p. 195;Philosophical Magazine, vol. xliv., p. 311.

[57]Science, June 26, 1903.

[58]Proceedings of the Chemical Society, March 2, 1888.

[59]Times, March 30, 1888.

[60]Encyclopædia Britannica, article 'Atom.'

[61]Fleming,Proceedings Royal Institution, vol. xvii., p. 169.

UNIVERSAL FORCES

Wefind it equally impossible to conceive of matter without force, as of force without matter. The two modes of action, or of being, are inseparable. Yet our minds strongly distinguish between them; they impart a dual aspect to the world. Phenomena are not simple manifestations of disembodied energy, if such a thing could be; they have a substantial basis which, nevertheless, eludes apprehension, and seems to slip away into nothingness if we try to empty it of its immaterial contents. Nor do these energize in the void. They and the bodies they animate are knowable only in combination, and exist, to our apprehension, only on the condition of mutual dependence. All we can do towards discriminating them is to fix our attentionpredominantly on one or the other side of things, and so facilitate thought by drawing ideal lines of demarcation.

Just as there are many forms of matter—all springing, we are led to believe, from an undifferentiated, fundamental world-stuff—so there are various kinds of force, reducible, possibly without exception, to one universal principle. Their correlation, indeed, has been already in large measure demonstrated; heat, light, electricity, and kinetic power are known to be equivalent and interchangeable; but there are outstanding activities, which resist assimilation, and seem to originate under different conditions from the rest. Forces manifest themselves chiefly through attractive and repulsive effects, varying in accordance with their natures and the modification of attendant circumstances. The minute particles of matter, for instance, cohere; they cling together tenaciously; yet no pressure avails to bring them into actual contact; at a certain point of mutual approach, they develop an invincible power of resistance to any further encroachments upon their separate molecular domains. And it is this faculty which gives to matter its distinctive property of hardness. It is rendered tangible to sense just by its recalcitrance to constraint.

Neither the mode of operation nor the nature of the forces by which molecules are organized into masses is known; while the power acting on the masses thus organized, and regulating by its action the mechanism of the universe, is fully as baffling to comprehension. Wonder at its results is blunted by familiarity; presented to us as novelties, they should be pronounced to outrage reason. The relations of gravity are of the utmost simplicity; and they are, on that very account, supremely perplexing. They are governed by one steadfast law, the same everywhere, and under all varieties of conditions within the range of experiment or precise observation. It governs impartially every kind and quality of matter, taking no notice of its states or combinations, ignoring its subjection to chemical, thermal, magnetic, or electrical influences. Gravity is not only indifferent, but inevitable and inexorable; there is no resisting its sway; no screen serves as a shelter against its persuasions; it spreads equably in all directions,becoming enfeebled, like wave-motion, in the strict proportion of its diffusion from a centre over successive spherical surfaces. Its most singular peculiarity, however, is its apparent unconcern with time. The gravitational pull is virtually instantaneous; its transmission—if it be transmitted—takes place millions of times faster than that of light; the finest tests have, so far, failed to elicit symptoms of delay. These would be found in minute discrepancies between calculated and observed perturbational effects in the heavens.

The action of gravity, if propagated with finite velocity, should differ for bodies preserving an invariable distance from its source, and for bodies travelling towards or away from it. Their movement would modify the law of attraction.[62]Yet, up to the present, it has proved impossible to detect the slightest deviation from the plain rule of inverse squares. Again, the penetrative faculty of this strange force seems absolute and unlimited. We know by ordinary experience that we cannot diminish the weight of an object byinterposing any kind of shield between it and the earth; and no refinement in experimentation avails to alter this result. That it is so, is a fortunate circumstance for the harmony of the world. We can dimly imagine the riot of confusion that would ensue if a transiting globe could intercept the attraction, as it does the light, of a central governing mass. But from the wonderfully adjusted universal order gravitational eclipses are excluded; nor does the densest body throw even the faintest gravitational shadow.

The nature of a power so singularly conditioned is almost inconceivable; yet attempts have not been wanting to fathom the mystery that surrounds it. Professor Osborne Reynolds, in the Rede Lecture for 1902, claimed to have arrived at 'a complete, quantitative, purely mechanical explanation of the cause of gravitation,' based on the 'dilatancy' of a granular medium in close piling. But his working model of the universe will probably be remembered only as a lesson in the 'inversion of ideas,' showing that with skill and ingenuity a fairly concordant outcome of phenomena may be derived from antagonistichypotheses. In this author's view matter is equivalent to a deficiency of mass, the spaces where his cosmic grains are relatively few, because their arrangement is out of gear, being driven towards one another by the pressure of the surrounding medium, in which they are compactly stowed, and therefore numerous. Thus, the acting forces in nature are made to depend upon the compression by the denser medium of interspatial tracts of rarer consistence, forming what we call matter. The theory is difficult, if not impossible of acceptance, not because it involves the overthrow of conceptions which may be rooted in habitual modes of thought, rather than in absolute truth, but because of its startling postulates and large vacuities. To be valid, it should be complete; and there are obvious chasms in the vast expanse of ground which it covers with surprising, though only partial success.

Themulta renascenturof the poet is verified by the revolutions no less of thought than of speech. Flights of minute material particles have served the turn of theorists often, and in more ways than one, and have as frequently been consigned to discredited oblivion; butthey are in vogue once more. George Louis Lesage, of Geneva, devoted sixty-three of the seventy-nine years of his life, which came to an end in 1803, to the elaboration of a mechanical rationale of gravity, first given to the world in theTransactionsof the Berlin Academy of Sciences for 1782, and with details of amplification in hisTraité de Physique Mécanique, edited by Pierre Prévost in 1818.[63]The explanation it offered of molar attractions was by the supposed unceasing impacts of 'ultramundane corpuscles,' speeding in countless numbers and at fabulous velocities, from nowhere everywhere, and thus enforcing the mutual approach of masses of gross matter. This involved the supposition of an infinitesimal screening effect, producing a small inequality in the strength of the bombardment on the sheltered and unsheltered sides of the bodies exposed to it. This inequality, in fact, was taken to be thecausa causansof gravity. Yet its production encountered a difficulty. There was required for it a trifling degree of opacity in every kindof matter, while perfect gravitational transparency is asserted by the most delicate observations. Lesage, then, reduced the arrests laid upon his particles to a minimum; one in ten thousand, for instance, might at the utmost be intercepted by the terrestrial globe.[64]Even this insignificant minority, however, would suffice, through the surrender of their momentum to the impeding bodies, to endow them with the noted property of gravitation.

Clerk Maxwell urged the objection that the accompanying loss of kinetic energy by the corpuscles should, if transformed into heat, render all gravitating bodies white-hot. But Professor J. J. Thomson holds that the transferred corpuscular energy might, instead of reappearing in thermal form, be converted into some highly penetrative species of radiation capable of escaping unperceived into surrounding space.[65]'A simple calculation,' he adds, '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 onegramme of radium.' This consequence of Lesage's theory takes one's breath away; the 'fables of the Talmud' seem, by comparison, easy of belief; nevertheless, Lord Kelvin[66]declared it in 1873 to be more complete in the expository sense, and not more arduous in its assumptions, than the kinetic theory of gases.

Its fundamental postulate, at any rate, has been curiously verified in the course of recent researches into the arcana of physics. Entities in some degree corresponding to the ultramundane corpuscles of the Genevese philosopher do actually exist. Electrons are being continually expelled from bodies in all parts of the universe; they issue forth under all conceivable conditions and in unlimited numbers. Space is perhaps thronged with them; no material object can be exempt from their multitudinous buffetings, which are beginning to be taken account of in many cosmical speculations, and cannot certainly be ignored in efforts to solve the most obvious to superficial apprehension, the most intricate on a profound consideration, of all cosmical problems. Butthere is one fatal objection to an electronic theory of gravitation. The agency appealed to travels too slowly to be available for the required purpose. The velocity of light, there is reason to believe, sets a limit impossible to be surpassed or even attained by the velocity of electrons; yet it is incomparably smaller than the rate of gravitational transmission.

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-inequality;[67]and this value may be taken as authentic. So colossal a discrepancy excludes any kind of impact-rationale of the mutual pull of heavy masses; Lesage's corpuscles remain 'ultramundane'; their identification with known atoms or sub-atoms appears to be precluded; no products of ionic disintegration possess the qualities necessarily to be ascribed to them.

We turn, then, inevitably to the menstruum of mysteries, the bank of the insolvent in speculation, to the all-serviceable ether. Etherealradiations exercise an impulsive power; light-pressure has secured a recognised status among cosmic agencies; 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 propagation. Professor J. J. Thomson, accordingly, considered that but for the drawback of their insufficient velocity, 'very penetrating Röntgen rays' might with advantage be substituted for corpuscular streams as the cause of gravity.[68]They would, in some slight degree, be absorbed by encountered masses, to which they would impart a proportionate amount of momentum. Two bodies mutually shadowing one another would, under such circumstances, be drawn together with a force varying as the inverse square of distance; and if further they absorbed the impinging rays strictly in the measure of their density (as observation shows to be approximately the case), the attraction would increase in the same ratio as the product of their masses. But Röntgen rays travel with the precise velocity of light; they are, in truth, ultra-invisible light; and they must hence beregarded as hopelessly incompetent to explain an influence transmitted at least six million times more rapidly.

This was fully admitted by Dr. H. A. Lorentz,[69]who, five years ago, weighed the vibrational hypothesis of gravity in the balance of rigorous calculation, and found it wanting. His equations yielded the unexpected result that, if its postulates were granted, the noted attractions between massive bodies could subsist only on the terms of an incessant waste of electro-magnetic energy. But this is of course inadmissible. The theory involving such a consequence stands self-condemned, to say nothing of the wholly inadequate rate of propagation afforded by it.

Impulsion hypotheses, whether by corpuscles or rays, being hopelessly discredited, Dr. Lorentz reverted to a half-forgotten speculation by Mosotti, which, though sixty years old, struck him as capable of being adapted to modern requirements. It was of an electrical nature, and, in the novel shape given to it, supposed gravitational action to depend uponstrains of the ether due to the disturbing effects of the positive and negative ions constituting ordinary matter. These 'states' of the medium are distinct in kind; they cannot neutralize one another; and the familiar law of attraction represents their resultant effect. To bring it about much has to be taken for granted; yet the hypothesis can lay claim to one singular prerogative. Although the disturbances invoked by it traverse the ether with no more than the standard speed of light, it appears from Dr. Lorentz's investigation that, owing to certain modifications in the properties of the medium produced by moving matter, the planetary perturbations betraying loss of time in gravitational transmission would, on the electrical theory, be so small as to evade detection. As regards this crucial point, the Dutch physicist has hit upon a felicity of explanation entirely original, and, as it were, unsought.

An 'undulatory theory' of gravity, adumbrated, rather than advanced by Mr. Whittaker in 1902,[70]excited hopes that the ideal aim of science—a complete unification of the forces ofNature—might at last be within reach. Based upon a striking mathematical research, it exhibited the attraction between masses as, in a manner, the integration of innumerable wave disturbances, propagated at a rate not strictly definable, but perhaps immensely surpassing that of gravity. No suggestion was made as to the primary mode or cause of agitation, yet it seemed much to learn that the medium we are cognizant of in space might be capable of transmitting the pull of gravity. Unfortunately, however, the physical foundation of this reassuring congruity proves to be weak or unsound. The mathematical mill works magnificently, but the grist put into it is of dubious quality. Stripping Mr. Whittaker's result of its purely analytical form, Dr. Johnstone Stoney showed that an assumption of extreme improbability lay concealed in his equations, which could not, he concluded, be seriously taken to correspond with the reality of things.[71]

There would then seem to be no alternative but to acceptad interimthe electro-dynamical view of the nature of gravity. If not true,it is at least not obviously false. Through its subtlety it escapes direct confutation. And the method of exclusions, by eliminating competitors, has left it in virtual possession of the field.

Nothing is more curious in the history of recent science than the continual and irresistible growth which it records in the importance of electrical phenomena. All others tend to become merged in them; the most varied data of experience claim to be translated into electrical terminology. They are not, assuredly, rendered more intelligible by the process, but it at any rate abolishes the confusion incidental to multitudinous points of view. Thus, in the last resort, we find electrical forces (if they may be so designated) swaying the world. What they essentially consist in, we cannot tell; the utmost that may reasonably be hoped for is to arrive at a clear conception of modes of action reduced to antagonistic stresses, by which the play and counterplay of the universe may be kept up. And to this extent we find it possible to understand how electricity works the ethereal machinery. It is strongly dualistic. Thenearer we get to the foundations of nature, the more sharply positive and negative charges appear to be differentiated.

The opinion is nevertheless held by some inquirers that negative electricity is the only substantive kind, and that its complement is ordinary matter deprived of some of its negative particles. This, in fact, revives Franklin's 'one fluid theory,' only with the substitution of negative for positive electricity as the active principle.[72]But we are met by the doubt whether 'ordinary matter' can be said to exist in and by itself. If it do, the mode of its existence becomes more and more baffling to comprehension, as the association of mass with charge makes its way into the foreground of thought.[73]Moreover, a charge is, or produces, a 'state of the ether' (to use the unsatisfactory current phrase); and the ether being capable of opposite distortions, the effects upon it of opposite charges are contrary and similar, though perhaps not equivalent; whence the 'two fluid theory' obtains aprimâ facierecommendation as the simplest, though a crudeinterpretation of electrical phenomena. These are ubiquitous; destitute though we are of sense-organs for their perception, we still indirectly recognise their presence on every side. If the unification of the forces in nature be attainable, the unifying formula will doubtless be derived from them. Electricity is themot de l'énigme; yet it is itself the most inscrutable of enigmas.

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