Now what the speed to matter's atoms given
     Thou mayest in few, my Memmius, learn from this:
     When first the dawn is sprinkling with new light
     The lands, and all the breed of birds abroad
     Flit round the trackless forests, with liquid notes
     Filling the regions along the mellow air,
     We see 'tis forthwith manifest to man
     How suddenly the risen sun is wont
     At such an hour to overspread and clothe
     The whole with its own splendour; but the sun's
     Warm exhalations and this serene light
     Travel not down an empty void; and thus
     They are compelled more slowly to advance,
     Whilst, as it were, they cleave the waves of air;
     Nor one by one travel these particles
     Of the warm exhalations, but are all
     Entangled and enmassed, whereby at once
     Each is restrained by each, and from without
     Checked, till compelled more slowly to advance.
     But the primordial atoms with their old
     Simple solidity, when forth they travel
     Along the empty void, all undelayed
     By aught outside them there, and they, each one
     Being one unit from nature of its parts,
     Are borne to that one place on which they strive
     Still to lay hold, must then, beyond a doubt,
     Outstrip in speed, and be more swiftly borne
     Than light of sun, and over regions rush,
     Of space much vaster, in the self-same time
     The sun's effulgence widens round the sky.
 
 
     Nor to pursue the atoms one by one,
     To see the law whereby each thing goes on.
     But some men, ignorant of matter, think,
     Opposing this, that not without the gods,
     In such adjustment to our human ways,
     Can nature change the seasons of the years,
     And bring to birth the grains and all of else
     To which divine Delight, the guide of life,
     Persuades mortality and leads it on,
     That, through her artful blandishments of love,
     It propagate the generations still,
     Lest humankind should perish. When they feign
     That gods have stablished all things but for man,
     They seem in all ways mightily to lapse
     From reason's truth: for ev'n if ne'er I knew
     What seeds primordial are, yet would I dare
     This to affirm, ev'n from deep judgment based
     Upon the ways and conduct of the skies—
     This to maintain by many a fact besides—
     That in no wise the nature of the world
     For us was builded by a power divine—
     So great the faults it stands encumbered with:
     The which, my Memmius, later on, for thee
     We will clear up. Now as to what remains
     Concerning motions we'll unfold our thought.
 
 
     Now is the place, meseems, in these affairs
     To prove for thee this too: nothing corporeal
     Of its own force can e'er be upward borne,
     Or upward go—nor let the bodies of flames
     Deceive thee here: for they engendered are
     With urge to upwards, taking thus increase,
     Whereby grow upwards shining grains and trees,
     Though all the weight within them downward bears.
     Nor, when the fires will leap from under round
     The roofs of houses, and swift flame laps up
     Timber and beam, 'tis then to be supposed
     They act of own accord, no force beneath
     To urge them up. 'Tis thus that blood, discharged
     From out our bodies, spurts its jets aloft
     And spatters gore. And hast thou never marked
     With what a force the water will disgorge
     Timber and beam? The deeper, straight and down,
     We push them in, and, many though we be,
     The more we press with main and toil, the more
     The water vomits up and flings them back,
     That, more than half their length, they there emerge,
     Rebounding. Yet we never doubt, meseems,
     That all the weight within them downward bears
     Through empty void. Well, in like manner, flames
     Ought also to be able, when pressed out,
     Through winds of air to rise aloft, even though
     The weight within them strive to draw them down.
     Hast thou not seen, sweeping so far and high,
     The meteors, midnight flambeaus of the sky,
     How after them they draw long trails of flame
     Wherever Nature gives a thoroughfare?
     How stars and constellations drop to earth,
     Seest not? Nay, too, the sun from peak of heaven
     Sheds round to every quarter its large heat,
     And sows the new-ploughed intervales with light:
     Thus also sun's heat downward tends to earth.
     Athwart the rain thou seest the lightning fly;
     Now here, now there, bursting from out the clouds,
     The fires dash zig-zag—and that flaming power
     Falls likewise down to earth.
 
 
                                 In these affairs
     We wish thee also well aware of this:
     The atoms, as their own weight bears them down
     Plumb through the void, at scarce determined times,
     In scarce determined places, from their course
     Decline a little—call it, so to speak,
     Mere changed trend. For were it not their wont
     Thuswise to swerve, down would they fall, each one,
     Like drops of rain, through the unbottomed void;
     And then collisions ne'er could be nor blows
     Among the primal elements; and thus
     Nature would never have created aught.
 
 
     But, if perchance be any that believe
     The heavier bodies, as more swiftly borne
     Plumb down the void, are able from above
     To strike the lighter, thus engendering blows
     Able to cause those procreant motions, far
     From highways of true reason they retire.
     For whatsoever through the waters fall,
     Or through thin air, must quicken their descent,
     Each after its weight—on this account, because
     Both bulk of water and the subtle air
     By no means can retard each thing alike,
     But give more quick before the heavier weight;
     But contrariwise the empty void cannot,
     On any side, at any time, to aught
     Oppose resistance, but will ever yield,
     True to its bent of nature. Wherefore all,
     With equal speed, though equal not in weight,
     Must rush, borne downward through the still inane.
     Thus ne'er at all have heavier from above
     Been swift to strike the lighter, gendering strokes
     Which cause those divers motions, by whose means
     Nature transacts her work. And so I say,
     The atoms must a little swerve at times—
     But only the least, lest we should seem to feign
     Motions oblique, and fact refute us there.
     For this we see forthwith is manifest:
     Whatever the weight, it can't obliquely go,
     Down on its headlong journey from above,
     At least so far as thou canst mark; but who
     Is there can mark by sense that naught can swerve
     At all aside from off its road's straight line?
 
 
     Again, if ev'r all motions are co-linked,
     And from the old ever arise the new
     In fixed order, and primordial seeds
     Produce not by their swerving some new start
     Of motion to sunder the covenants of fate,
     That cause succeed not cause from everlasting,
     Whence this free will for creatures o'er the lands,
     Whence is it wrested from the fates,—this will
     Whereby we step right forward where desire
     Leads each man on, whereby the same we swerve
     In motions, not as at some fixed time,
     Nor at some fixed line of space, but where
     The mind itself has urged? For out of doubt
     In these affairs 'tis each man's will itself
     That gives the start, and hence throughout our limbs
     Incipient motions are diffused. Again,
     Dost thou not see, when, at a point of time,
     The bars are opened, how the eager strength
     Of horses cannot forward break as soon
     As pants their mind to do? For it behooves
     That all the stock of matter, through the frame,
     Be roused, in order that, through every joint,
     Aroused, it press and follow mind's desire;
     So thus thou seest initial motion's gendered
     From out the heart, aye, verily, proceeds
     First from the spirit's will, whence at the last
     'Tis given forth through joints and body entire.
     Quite otherwise it is, when forth we move,
     Impelled by a blow of another's mighty powers
     And mighty urge; for then 'tis clear enough
     All matter of our total body goes,
     Hurried along, against our own desire—
     Until the will has pulled upon the reins
     And checked it back, throughout our members all;
     At whose arbitrament indeed sometimes
     The stock of matter's forced to change its path,
     Throughout our members and throughout our joints,
     And, after being forward cast, to be
     Reined up, whereat it settles back again.
     So seest thou not, how, though external force
     Drive men before, and often make them move,
     Onward against desire, and headlong snatched,
     Yet is there something in these breasts of ours
     Strong to combat, strong to withstand the same?—
     Wherefore no less within the primal seeds
     Thou must admit, besides all blows and weight,
     Some other cause of motion, whence derives
     This power in us inborn, of some free act.—
     Since naught from nothing can become, we see.
     For weight prevents all things should come to pass
     Through blows, as 'twere, by some external force;
     But that man's mind itself in all it does
     Hath not a fixed necessity within,
     Nor is not, like a conquered thing, compelled
     To bear and suffer,—this state comes to man
     From that slight swervement of the elements
     In no fixed line of space, in no fixed time.
 
 
     Nor ever was the stock of stuff more crammed,
     Nor ever, again, sundered by bigger gaps:
     For naught gives increase and naught takes away;
     On which account, just as they move to-day,
     The elemental bodies moved of old
     And shall the same hereafter evermore.
     And what was wont to be begot of old
     Shall be begotten under selfsame terms
     And grow and thrive in power, so far as given
     To each by Nature's changeless, old decrees.
     The sum of things there is no power can change,
     For naught exists outside, to which can flee
     Out of the world matter of any kind,
     Nor forth from which a fresh supply can spring,
     Break in upon the founded world, and change
     Whole nature of things, and turn their motions about.