On the Nature of Things by Lucretius — Book IV, How sight and the senses work

Bodies that strike the eyes, awaking sight.
From certain things flow odours evermore,
As cold from rivers, heat from sun, and spray
From waves of ocean, eater-out of walls
Around the coasts. Nor ever cease to flit
The varied voices, sounds athrough the air.
²²²Then too there comes into the mouth at times
The wet of a salt taste, when by the sea
We roam about; and so, whene'er we watch
The wormword being mixed, its bitter stings.
To such degree from all things is each thing
Borne streamingly along, and sent about
To every region round; and nature grants
²²⁷Nor rest nor respite of the onward flow,
Since 'tis incessantly we feeling have,
And all the time are suffered to descry
And smell all things at hand, and hear them sound.

²³⁰Besides, since shape examined by our hands
Within the dark is known to be the same
As that by eyes perceived within the light
And lustrous day, both touch and sight must be
By one like cause aroused. So, if we test
A square and get its stimulus on us
²³⁵Within the dark, within the light what square
Can fall upon our sight, except a square
That images the things? Wherefore it seems
The source of seeing is in images,
Nor without these can anything be viewed.
Now these same films I name are borne about
²⁴⁰And tossed and scattered into regions all.
But since we do perceive alone through eyes,
It follows hence that whitherso we turn
Our sight, all things do strike against it there
With form and hue. And just how far from us
Each thing may be away, the image yields
²⁴⁵To us the power to see and chance to tell:
For when 'tis sent, at once it shoves ahead
And drives along the air that's in the space
Betwixt it and our eyes. And thus this air
All glides athrough our eyeballs, and, as 'twere,
Brushes athrough our pupils and thuswise
Passes across. Therefore it comes we see
²⁵⁰How far from us each thing may be away,
And the more air there be that's driven before,
And too the longer be the brushing breeze
Against our eyes, the farther off removed
Each thing is seen to be: forsooth, this work
With mightily swift order all goes on,
So that upon one instant we may see
²⁵⁵What kind the object and how far away.
Nor over-marvellous must this be deemed
In these affairs that, though the films which strike
Upon the eyes cannot be singly seen,
The things themselves may be perceived. For thus
When the wind beats upon us stroke by stroke
And when the sharp cold streams, 'tis not our wont
²⁶⁰To feel each private particle of wind
Or of that cold, but rather all at once;
And so we see how blows affect our body,
As if one thing were beating on the same
And giving us the feel of its own body
Outside of us. Again, whene'er we thump
²⁶⁵With finger-tip upon a stone, we touch
But the rock's surface and the outer hue,
Nor feel that hue by contact- rather feel
The very hardness deep within the rock.

²⁶⁹Now come, and why beyond a looking-glass
An image may be seen, perceive. For seen
It soothly is, removed far within.
'Tis the same sort as objects peered upon
Outside in their true shape, whene'er a door
Yields through itself an open peering-place,
And lets us see so many things outside
Beyond the house. Also that sight is made
²⁷⁴By a twofold twin air: for first is seen
The air inside the door-posts; next the doors,
The twain to left and right; and afterwards
A light beyond comes brushing through our eyes,
Then other air, then objects peered upon
Outside in their true shape. And thus, when first
²⁷⁹The image of the glass projects itself,
As to our gaze it comes, it shoves ahead
And drives along the air that's in the space
Betwixt it and our eyes, and brings to pass
That we perceive the air ere yet the glass.
But when we've also seen the glass itself,
²⁸⁴Forthwith that image which from us is borne
Reaches the glass, and there thrown back again
Comes back unto our eyes, and driving rolls
Ahead of itself another air, that then
'Tis this we see before itself, and thus
It looks so far removed behind the glass.
²⁸⁹Wherefore again, again, there's naught for wonder
. . . . . .
In those which render from the mirror's plane
A vision back, since each thing comes to pass
By means of the two airs. Now, in the glass
The right part of our members is observed
Upon the left, because, when comes the image
²⁹⁴Hitting against the level of the glass,
'Tis not returned unshifted; but forced off
Backwards in line direct and not oblique,-
Exactly as whoso his plaster-mask
Should dash, before 'twere dry, on post or beam,
And it should straightway keep, at clinging there,
²⁹⁹Its shape, reversed, facing him who threw,
And so remould the features it gives back:
It comes that now the right eye is the left,
The left the right.

³⁰²An image too may be
From mirror into mirror handed on,
Until of idol-films even five or six
Have thus been gendered. For whatever things
Shall hide back yonder in the house, the same,
However far removed in twisting ways,
³⁰⁷May still be all brought forth through bending paths
And by these several mirrors seen to be
Within the house, since nature so compels
All things to be borne backward and spring off
At equal angles from all other things.
To such degree the image gleams across
From mirror unto mirror; where 'twas left
It comes to be the right, and then again
Returns and changes round unto the left.
³¹²Again, those little sides of mirrors curved
Proportionate to the bulge of our own flank
Send back to us their idols with the right
Upon the right; and this is so because
Either the image is passed on along
From mirror unto mirror, and thereafter,
When twice dashed off, flies back unto ourselves;
Or else the image wheels itself around,
When once unto the mirror it has come,
³¹⁷Since the curved surface teaches it to turn
³²²To usward. Further, thou might'st well believe
That these film-idols step along with us
And set their feet in unison with ours
And imitate our carriage, since from that
Part of a mirror whence thou hast withdrawn
Straightway no images can be returned.
Further, our eye-balls tend to flee the bright
And shun to gaze thereon; the sun even blinds,
If thou goest on to strain them unto him,
Because his strength is mighty, and the films
Heavily downward from on high are borne
³²⁷Through the pure ether and the viewless winds,
And strike the eyes, disordering their joints.
So piecing lustre often burns the eyes,
Because it holdeth many seeds of fire
Which, working into eyes, engender pain.
³³²Again, whatever jaundiced people view
Becomes wan-yellow, since from out their bodies
Flow many seeds wan-yellow forth to meet
The films of things, and many too are mixed
Within their eye, which by contagion paint
All things with sallowness.

³³⁷Again, we view
From dark recesses things that stand in light,
Because, when first has entered and possessed
The open eyes this nearer darkling air,
Swiftly the shining air and luminous
Followeth in, which purges then the eyes
And scatters asunder of that other air
³⁴²The sable shadows, for in large degrees
This air is nimbler, nicer, and more strong.
And soon as ever 'thas filled and oped with light
The pathways of the eyeballs, which before
Black air had blocked, there follow straightaway
³⁴⁷Those films of things out-standing in the light,
Provoking vision- what we cannot do
From out the light with objects in the dark,
Because that denser darkling air behind
Followeth in, and fills each aperture
And thus blockades the pathways of the eyes
³⁵²That there no images of any things
Can be thrown in and agitate the eyes.
And when from far away we do behold
The squared towers of a city, oft
Rounded they seem,- on this account because
Each distant angle is perceived obtuse,
Or rather it is not perceived at all;
³⁵⁷And perishes its blow nor to our gaze
Arrives its stroke, since through such length of air
Are borne along the idols that the air
Makes blunt the idol of the angle's point
By numerous collidings. When thuswise
The angles of the tower each and all
Have quite escaped the sense, the stones appear
As rubbed and rounded on a turner's wheel-
³⁶²Yet not like objects near and truly round,
But with a semblance to them, shadowily.
Likewise, our shadow in the sun appears
To move along and follow our own steps
And imitate our carriage- if thou thinkest
Air that is thus bereft of light can walk,
³⁶⁷Following the gait and motion of mankind.
For what we use to name a shadow, sure
Is naught but air deprived of light. No marvel:
Because the earth from spot to spot is reft
Progressively of light of sun, whenever
In moving round we get within its way,
³⁷²While any spot of earth by us abandoned
Is filled with light again, on this account
It comes to pass that what was body's shadow
Seems still the same to follow after us
In one straight course. Since, evermore pour in
New lights of rays, and perish then the old,
Just like the wool that's drawn into the flame.
³⁷⁷Therefore the earth is easily spoiled of light
And easily refilled and from herself
Washeth the black shadows quite away.

³⁷⁹And yet in this we don't at all concede
That eyes be cheated. For their task it is
To note in whatsoever place be light,
In what be shadow: whether or no the gleams
Be still the same, and whether the shadow which
Just now was here is that one passing thither,
Or whether the facts be what we said above,
³⁸⁴'Tis after all the reasoning of mind
That must decide; nor can our eyeballs know
The nature of reality. And so
Attach thou not this fault of mind to eyes,
Nor lightly think our senses everywhere
Are tottering. The ship in which we sail
Is borne along, although it seems to stand;
The ship that bides in roadstead is supposed
There to be passing by. And hills and fields
³⁸⁹Seem fleeing fast astern, past which we urge
The ship and fly under the bellying sails.
The stars, each one, do seem to pause, affixed
To the ethereal caverns, though they all
Forever are in motion, rising out
And thence revisiting their far descents
When they have measured with their bodies bright
³⁹⁴The span of heaven. And likewise sun and moon
Seem biding in a roadstead,- objects which,
As plain fact proves, are really borne along.
Between two mountains far away aloft
From midst the whirl of waters open lies
A gaping exit for the fleet, and yet
³⁹⁹They seem conjoined in a single isle.
When boys themselves have stopped their spinning round,
The halls still seem to whirl and posts to reel,
Until they now must almost think the roofs
Threaten to ruin down upon their heads.
⁴⁰⁴And now, when nature begins to lift on high
The sun's red splendour and the tremulous fires,
And raise him o'er the mountain-tops, those mountains-
O'er which he seemeth then to thee to be,
His glowing self hard by atingeing them
With his own fire- are yet away from us
Scarcely two thousand arrow-shots, indeed
⁴⁰⁹Oft scarce five hundred courses of a dart;
Although between those mountains and the sun
Lie the huge plains of ocean spread beneath
The vasty shores of ether, and intervene
A thousand lands, possessed by many a folk
And generations of wild beasts. Again,

⁴¹⁴A pool of water of but a finger's depth,
Which lies between the stones along the pave,
Offers a vision downward into earth
As far, as from the earth o'erspread on high
The gulfs of heaven; that thus thou seemest to view
Clouds down below and heavenly bodies plunged
⁴¹⁹Wondrously in heaven under earth.
Then too, when in the middle of the stream
Sticks fast our dashing horse, and down we gaze
Into the river's rapid waves, some force
Seems then to bear the body of the horse,
Though standing still, reversely from his course,
And swiftly push up-stream. And wheresoe'er
⁴²⁴We cast our eyes across, all objects seem
Thus to be onward borne and flow along
In the same way as we. A portico,
Albeit it stands well propped from end to end
On equal columns, parallel and big,
⁴²⁹Contracts by stages in a narrow cone,
When from one end the long, long whole is seen,-
Until, conjoining ceiling with the floor,
And the whole right side with the left, it draws
Together to a cone's nigh-viewless point.
To sailors on the main the sun he seems
From out the waves to rise, and in the waves
To set and bury his light- because indeed
⁴³⁴They gaze on naught but water and the sky.
Again, to gazers ignorant of the sea,
Vessels in port seem, as with broken poops,
To lean upon the water, quite agog;
For any portion of the oars that's raised
Above the briny spray is straight, and straight
⁴³⁹The rudders from above. But other parts,
Those sunk, immersed below the water-line,
Seem broken all and bended and inclined
Sloping to upwards, and turned back to float
Almost atop the water. And when the winds
Carry the scattered drifts along the sky
In the night-time, then seem to glide along
⁴⁴⁴The radiant constellations 'gainst the clouds
And there on high to take far other course
From that whereon in truth they're borne. And then,

⁴⁴⁷If haply our hand be set beneath one eye
And press below thereon, then to our gaze
Each object which we gaze on seems to be,
By some sensation twain- then twain the lights
Of lampions burgeoning in flowers of flame,
And twain the furniture in all the house,
⁴⁵²Two-fold the visages of fellow-men,
And twain their bodies. And again, when sleep
Has bound our members down in slumber soft
And all the body lies in deep repose,
Yet then we seem to self to be awake
And move our members; and in night's blind gloom
⁴⁵⁷We think to mark the daylight and the sun;
And, shut within a room, yet still we seem
To change our skies, our oceans, rivers, hills,
To cross the plains afoot, and hear new sounds,
Though still the austere silence of the night
Abides around us, and to speak replies,
Though voiceless. Other cases of the sort
⁴⁶²Wondrously many do we see, which all
Seek, so to say, to injure faith in sense-
In vain, because the largest part of these
Deceives through mere opinions of the mind,
Which we do add ourselves, feigning to see
What by the senses are not seen at all.
⁴⁶⁷For naught is harder than to separate
Plain facts from dubious, which the mind forthwith
Adds by itself.