The last source of superst.i.tion is our ignorance of the causes of natural phenomena--

Praesertim rebus in illis Quae supera caput aetheriis cernuntur in oris[15].

Hence the sixth book is devoted to the explanation of thunderstorms, tempests, volcanoes, earthquakes, and the like,--phenomena which are generally attributed to the direct agency of the G.o.ds. The whole work terminates with an account of the Plague at Athens, closely following that given by Thucydides.

The first question which arises after a review of the whole argument is that suggested by the statement of Jerome, and brought into prominence since the publication of Lachmann's edition of Lucretius, viz. whether there is good reason for believing that the poem was left by the author in an unfinished state. In answering this question, it is to be observed, on the one hand, that there is no incompleteness in the fulfilment of the original plan of the work, unless from one or two hints[16] we conclude that the poet intended giving a fuller account of the blessed state of the G.o.ds than that given at iii.

17-24. He announces at i. 54, etc., and again at i. 127, etc., the design of the poem as embracing the first principles of natural philosophy, and the application of these principles to certain special subjects, viz. the nature of soul and body, the origin of the belief in ghosts, the natural causes of creation, and the meaning of certain celestial phenomena.

The practical purpose of the poem--the overthrow of superst.i.tion--limits the argument to these subjects of discussion.

They are severally mentioned where the argument is resumed in Books iii, iv, v, and vi, as those matters which require a clear explanation from the poet. All the topics enunciated in the opening statement are discussed with the utmost fulness. The great strongholds of superst.i.tion are attacked and overthrown in regular succession. In the introduction to the sixth book, the lines (91-95)

Tu mihi supremae praescribta ad candida calcis, etc.

clearly show that the poet considered himself approaching the end of his task.

But, on the other hand, an examination of the poem in detail leads to the conclusion that it did not receive its author's final touch. The continuity of the argument is occasionally broken in all the books except the first. In the fourth, fifth, and sixth, especially, these breaks are very frequent, and there are more frequent instances in them of repet.i.tion and careless workmanship. They extend also to a greater length than the earlier books, which would naturally be the case if they had not received the author's final revision. The poem throughout gives the impression of great fulness of matter--

Usque adeo largos haustus e fontibu' magnis Lingua meo suavis diti de pectore fundet;--

and in the composition of these later books, new suggestions seem to have been constantly occurring to the poet as new materials were added to his stores of knowledge: and the first draft of his argument has not been recast so as to incorporate and harmonise them with it. The pa.s.sages containing these new materials appear to have been fitted into the place which they now occupy in the work, not always very judiciously, either by Cicero or some other editor.

It was also part of the author's design to enunciate his deepest thoughts on the G.o.ds, on Nature, and on human life in more highly finished digressions from the main argument. Such pa.s.sages are, in general, introduced at the beginning and the end of the different books. They seem to bring out the more catholic interest which underlies the special subject of the poem. Some of these pa.s.sages are highly finished, and were evidently fixed by the poet in the places which he designed them to occupy. Such are, especially, the introductions to the first, second, and third books, and the concluding pa.s.sages of the second and third. But the repet.i.tion of a pa.s.sage of the first book as the introduction to the fourth, the long break in the continuity of the introduction to the fifth, the unfinished style of that to the sixth, and the abrupt and episodical conclusion to the whole poem (when contrasted with its elaborately artistic introduction), show that the same cause which marred the symmetry of his argument deprived it of the finished execution of a work of art. Yet these books--especially the fifth--are as rich in poetical feeling and substance as the earlier ones. The eye and hand of the master are as powerful as in the first enthusiasm with which he dedicated himself to his task, but they are less certain in their action. Whether his powers became intermittent owing to the attacks of illness, or whether his habit was to work roughly in the first instance and to perfect his work by subsequent revision, which in the case of his latest labours was prevented by death, must remain uncertain. It is a noticeable result of the vastness of the tasks which Roman genius set before itself, that two such works as the didactic poem of Lucretius and the Aeneid of Virgil were left unfinished by their authors, and given to the world in a more or less imperfect condition by other hands.

The poem, though incomplete in regard to the arrangement of its materials and artistic finish, presents a full and clear view of the philosophy accepted and expounded by Lucretius. What, then, is the intellectual interest and value of the work, considered as a great argument, in which the plan of Nature is explained, and the position of man in relation to that plan is determined? Is it true, as an ill.u.s.trious modern critic[17] has said, that 'the greatest didactic poem in any language was written in defence of the silliest and meanest of all systems of natural and moral philosophy'? Is this work a mere maze of ingeniously woven error, enriched with a few brilliant colours which have not yet faded with the lapse of time? or is it a great monument of the ancient mind, marking indeed its limitations, but at the same time perpetuating the memory of its native strength and energy? Has all the meaning of this controversy between science in its infancy and the pagan mythology in its decrepitude pa.s.sed away, as from the vantage-ground of nineteen centuries the blindness and the ignorance of both combatants are apparent? Or, may we not rather discern that amid all the confusion of this dim [Greek: nyktomachia]

a great cause was at issue; that truths the most vital to human wellbeing were involved on both sides; and that some positions were then gained which are not now abandoned?

In estimating the strength and the weakness of the system expounded by Lucretius, it is necessary to distinguish between the exposition of the principles of the atomic philosophy, contained in the first two books, and the explanation of natural phenomena contained in the remaining books. The first, notwithstanding some arbitrary and unverifiable a.s.sumptions, represents a real and important stage in the progress of enquiry; the second, although containing many striking observations and immediate inferences from the facts and processes of Nature, is, from the point of view of modern science, to be regarded mainly, as a curious page in the records of human error. Whatever may be said of the Epicurean additions to the system, it seems to be admitted that the original hypothesis of Democritus has been more pregnant in results, and has more affinity with the most advanced physical speculations of modern times, than the doctrines of all the other philosophers of antiquity. But even amid the ma.s.s of unwarranted a.s.sumptions and erroneous explanations contained in the later books, the topics discussed--such as the relation of the mind to the body, the mode by which sensible impressions are conveyed to the mind, the processes by which our globe a.s.sumed its present form, the origin of life, the evolution of humanity from its lowest to its higher stages of development, the origin of spiritual beliefs, of the humaner sentiments, of language, etc.--possess the interest of being kindred to those on which speculative activity is most employed in the present day. If the study of Lucretius forces upon our minds the arbitrary a.s.sumptions, the inadequate method, and the false conclusions of ancient science, it enables us to appreciate the disinterested greatness of its aims, and the enlightened curiosity which sought to solve the vastest problems.

It might be said, generally, that the argument of Lucretius was an attempt to give a philosophical description of Nature before the advent of physical science. But, as a means of throwing light on the inadequacy of such speculations, it may be well to consider in detail some of those points where the argument most obviously fails in premises, method, and results.

The ancient as well as the modern enquirer into the truth of things was confronted with the question of the origin of all our knowledge.

Is knowledge obtained originally through the exercise of the reason or the senses, or through their combined and inseparable action? To this question Lucretius distinctly answers, that the senses are the foundation of all our knowledge.[18] They are our 'prima fides': the basis not only of all sound inference, but of all human conduct. The very conception of the meaning of true and false is derived from the senses:--

Invenies primis ab sensibus esse creatam Not.i.tiam veri neque sensus posse refelli[19].

But besides the direct action of outward things on the senses, he admits the power of certain images to make themselves immediately present to the mind (iv. 722-822), and also a certain immediate apprehension or intuition of the mind (iniectus animi) into things beyond the cognisance of sense[20]. Thus there is no actual inconsistency with his principles in claiming the power of understanding the properties and configuration of the atoms, which are represented as lying below the reach of our senses--

Omnis enim longe nostris ab sensibus infra Primorum natura iacet.

But of the mode of operation of this 'intuition of the mind' there is no criterion. The doctrine of the properties, shapes, motions, etc.

of the atoms is a creation of the imagination, suggested by certain a.n.a.logies from sensible things, but incapable of being verified by the senses, which he regards as the only sure foundations of knowledge.

But even on the supposition that the existence and properties of the atoms had been satisfactorily established, no adequate explanation is offered of their relation to the facts of existence. The same difficulty is encountered at the outset of this as of all other ancient systems of ontology, viz. how to pa.s.s from the eternal and immutable forms of the atoms to the variety and transitory nature of sensible objects. This is the very difficulty which Lucretius himself urges against the system of Herac.l.i.tus,--

Nam cur tam variae res possint esse requiro, Ex uno si sunt igni puroque creatae.

The order of Nature now subsisting is declared to be the result of the manifold combination of the atoms through infinite time and s.p.a.ce, but the intermediate stages by which this process was effected are a.s.sumed rather than investigated. We seem to pa.s.s 'per saltum' from the chaos of lifeless elements to the perfect order and manifold life of our system. This wide chasm seems as little capable of being bridged by the help of the atoms of Democritus, as by the watery element of Thales or the fiery element of Herac.l.i.tus. But in Lucretius this difficulty is partially concealed, by a poetical element in his conception, really inconsistent with the mechanical materialism on which his philosophy professes to be based.--It is to be observed that while the Greek word [Greek: atoma] implies merely the notion of individual existences, the words used by Lucretius, 'semina,'

'genitalia corpora,' really indicate a creative capacity in these existences. In conceiving their power of carrying on and sustaining the order of Nature, his imagination is thus aided by the a.n.a.logy of the growth of plants and living beings. A secret faculty in the atoms, distinct from their other properties, is a.s.sumed. Thus he says--

At primordia gignundis in rebus oportet Naturam clandestinam caecamque adhibere[21].

In his statement of the doctrine of the _Clinamen_, or slight declension in the motion of the atoms, so as 'to break the chain of fate,' he attributes to them a power a.n.a.logous to volition in living beings. This doctrine is suggested by the necessity of explaining contingency in Nature and freedom in the movements of sentient beings.

We are, as in all attempts to account for creation, forced back on the thought of an ultimate unexplained power in virtue of which things have been created and are maintained in being.

The Lucretian hypothesis of the atoms, even if it were accepted as the most reasonable explanation of the original const.i.tution of matter, is, by itself, altogether inadequate as a key to the secret of Nature.

It cannot be shown either how these atoms succeeded in arranging themselves in order, or how from their negative properties all positive life has been produced. The explanation of physical phenomena given in the four last books, as to the nature of our bodies and souls,--as to the action of outward things on the senses,--the origin and existence of the sun and moon, the earth and the living beings upon it, etc., although professedly deduced from the principles established in the first two books, are really reached independently.

They are either immediate inferences from the obvious intimations of sense, or they are the suggestions of a.n.a.logy.

The weakness as well as the strength of ancient science lay in its perception of a.n.a.logies. The mind of Lucretius was both under the influence of earlier a.n.a.logical conceptions, and also shows great boldness and originality in the logical and poetical apprehension of 'those same footsteps of Nature, treading on diverse subjects or matters.' But, in common with the earlier enquirers of Greece, he trusts too implicitly to their guidance through all his daring adventure. He seems to believe that the hidden properties of things are as open to discovery through this 'lux subl.u.s.tris' of the imagination, as through the 'lucida tela' of the reason.

To take one prominent instance of this influence, it is remarkable how, in his explanation of our mundane system, he is both consciously and unconsciously guided by the a.n.a.logy of the human body. Even Lucretius, living in the very meridian of ancient science, cannot in imagination absolutely emanc.i.p.ate himself from the a.s.sociations of mythology. He is indeed conscious of the inconsistency of attributing life and sense to the earth: yet not only does he speak poetically of Earth being the creative mother, Aether the fructifying father of all things, but his whole conception of the creation of the world is derived from a supposed likeness between the properties of our terrestrial and celestial systems, and those of living beings. Thus we read--

Undique quandoquidem per caulas aetheris omnis Et quasi per magni circ.u.m spiracula mundi Exitus introitusque elementis redditus extat[22].

Of the growth of plants and herbage it is said--

Ut pluma atque pili primum saetaeque creantur Quadripedum membris et corpore pennipotentum, Sic nova tum tellus herbas virgultaque primum Sustulit, inde loci mortalia saecla creavit[23].

From v. 535 to 563 the power of the air in supporting the earth 'in media mundi regione' is compared with the power which the delicate vital principle has in supporting the human body. Again, the gathering together of the waters of the sea is thus represented--

Tam magis expressus salsus de corpore sudor Augebat mare manando camposque natantis[24].

And finally, though it would be easy to multiply such quotations, the striking account, at the end of the second book, of the growth and the decay of our world is drawn directly from the obvious appearances of the growth and decay of the human body; e.g.--

Quoniam nec venae perpetiuntur Quod satis est neque quantum opus est natura ministrat[25].

As a necessary result of a system of natural philosophy based on a.s.sumptions, largely ill.u.s.trated indeed, but not corroborated by the observation of phenomena, with no verification of experiment or ascertainment of special laws, there is throughout the poem the utmost hardihood of a.s.sertion and inference on many points, on which modern science clearly proves this system to have been as much in error as it was possible to be. It is strange to note how inadequate an idea Lucretius had of the vastness and complexity of the problem which he professed to solve. He has no real conception of the progressive advance of knowledge, and of the necessity of patiently building on humble foundations. The striking lines--

Namque alid ex alio clarescet nec tibi caeca Nox iter eripiet quin ultima naturai Pervideas: ita res accendent lumina rebus[26],

look rather like an unconscious prophecy of the future progress of science than an account of the process of enquiry exhibited in the book.

A few out of many erroneous a.s.sertions about physical facts, in regard to some of which the opinions of Lucretius are behind the science even of his own time, may be noticed. Thus, at i. 1025, the existence of the Antipodes is denied. Again, in Book iii. the mind is stated to be a material substance, seated in the centre of the breast, composed of very minute particles, the relative proportions of which determine the characters both of men and animals. Lucretius shows a close and subtle observation of facts that establish the interdependence of mind and body, but no suspicion of that interdependence being connected with the functions of the brain and nervous system. His whole account of the _mundus_, of the earth at rest in the centre, and of the rolling vault of heaven, with its sun and moon and stars--'trembling fires in the vault'--all no larger than they appear to our eyes, is given without any notion of the inadequacy of his data to bear out his conclusions. The science which satisfied Epicurus was on astronomical and meteorological questions behind that attained by the mathematicians of Alexandria: and thus some of the conclusions enunciated by Virgil in the Georgics are nearer the truth than those accepted by Lucretius. While enlarging on the variety and subtlety in the combinations of his imaginary atoms, he has no adequate idea of the variety and subtlety in the real forces of Nature. His observation of the outward and visible appearances of things is accurate and vivid: there is often great ingenuity as well as a true apprehension of logical conditions in his processes of reasoning both from ideas and from phenomena: yet most of his conclusions as to the facts of Nature, which are not immediately perceptible to the senses, are mere fanciful explanations, indicating, indeed, a lively curiosity, but no real understanding of the true conditions of the enquiry. The root of his error lies in his not feeling how little can be known of the processes and facts of Nature by ordinary observation, without the resources of experiment and of scientific method built upon experiment.

The weak points of this philosophy, the mistaken aim and incomplete method of enquiry, the real ignorance of facts disguised under an appearance of systematic treatment, the unproductiveness of the results for any practical accession to man's power over Nature, are quite obvious to any modern reader, who, without any special study of physical science, cannot help being familiar with information which is now universally diffused, but which was beyond the reach of the most ardent enquirers and original thinkers of antiquity. But the amount of information possessed by different ages, or by different men, is no criterion of their relative intellectual power. The mental force of a strong and adventurous thinker may be recognised struggling even through these mists of error. The weakness of the system, interpreted by Lucretius, is the necessary weakness of the childhood of knowledge.

But along with the weakness and the ignorance there are also the keen feeling, the clear eye, and the buoyant fancies of early years,--the germs and the promise of a strong maturity.

The full light in which ancient poetry, history, and mental philosophy can still be read, makes us apt to forget that a great part even of the intellectual life of antiquity has left scarcely any record of itself. Of one aspect of this intellectual life Lucretius is the most complete exponent. The genius of Plato and Aristotle has been estimated, perhaps, as justly in modern as in ancient times. But the great intellectual life of such men as Democritus, Empedocles, or Anaxagoras, escapes our notice in the more familiar studies of cla.s.sical literature. The work of Lucretius reminds us of the intensity of thought and feeling, the clearness and minuteness of observation, with which the earliest enquiries into Nature were carried on. In some respects the general ignorance of the times enhances our sense of the greatness of individual philosophers. Each new attempt to understand the world was an original act of creative power. The intellectual strength and enthusiasm displayed by the poet himself may be regarded as some measure of the strength of the masters, who filled his mind with affection and astonishment.

The history of the physical science of the ancients cannot, indeed, be regarded as so interesting or important as that of their metaphysical philosophy. And this is so, not only on account of the comparative scantiness of their real acquisitions in the one as compared with the ideas and method which they have contributed to the other, and with the masterpieces which they have added to its literature; but still more on this account, that in physical knowledge new discovery supplants the place of previous error or ignorance, and can be understood without reference to what has been supplanted; whereas the power and meaning of philosophical ideas is unintelligible, apart from the knowledge of their origin and development. The history of physical science in ancient times affords satisfaction to a natural curiosity, but is not an indispensable branch of scientific study. The history of ancient mental philosophy, on the other hand,--the source not only of most of our metaphysical ideas and terms, but of many of the most familiar thoughts and words in daily use,--is the basis of all speculative study. Yet among the various kinds of interest which this poem has for different cla.s.ses of modern readers this is not to be forgotten, that it enables a student of science to estimate the actual discoveries, and, still more, the prognostications of discovery attained by the irregular methods of early enquiry. The school of philosophy to which Lucretius belonged was distinguished above other schools for the attention which it gave to the facts of Nature.

Though he himself makes no claim to original discovery, he yet shows a philosophical grasp of the whole system which he adopted, and a rigorous study of its details. He does not, like Virgil, merely reproduce some general results of ancient physics, to enhance the poetical conception of Nature: as he is not satisfied with those general results about human life and the origin of man, which amused a meditative poet and practical epicurean like Horace. He was a real student both of the plan of Nature and of man's relation to it. Out of the stores of his abundant information the modern reader may best learn not only the errors but also the happy guesses and pregnant suggestions of ancient science.

To the general reader there is another aspect, in which it is interesting to compare these germs of physical knowledge with some tendencies of scientific enquiry in modern times. The questions, vitally affecting the position of man in the world, which are discussed or raised by Lucretius in the course of his argument, are parallel to certain questions which have risen into prominence in connexion with the increasing study of Nature. Most conspicuous among these is the relation of physical enquiry to religious belief.

Expressions such as this,

Impia te rationis inire elementa viamque Indugredi sceleris,

show that scientific enquiry had to encounter the same prejudice in ancient as in modern times. The insufficiency and audacity of human reason were reprobated by the antagonists of Lucretius as they often are in the present day. Ancient religion denounced those who investigated the origin of sun, earth, and sky, as