And so in first place, then
With thunder are shaken the blue deeps of heaven,
Because the ethereal clouds, scudding aloft,
Together clash, what time 'gainst one another
The winds are battling. For never a sound there come
From out the serene regions of the sky;
But wheresoever in a host more dense
The clouds foregather, thence more often comes
A crash with mighty rumbling. And, again,
Clouds cannot be of so condensed a frame
As stones and timbers, nor again so fine
As mists and flying smoke; for then perforce
They'd either fall, borne down by their brute weight,
Like stones, or, like the smoke, they'd powerless be
To keep their mass, or to retain within
Frore snows and storms of hail. And they give forth
O'er skiey levels of the spreading world
A sound on high, as linen-awning, stretched
O'er mighty theatres, gives forth at times
A cracking roar, when much 'tis beaten about
Betwixt the poles and cross-beams. Sometimes, too,
Asunder rent by wanton gusts, it raves
And imitates the tearing sound of sheets
Of paper- even this kind of noise thou mayst
In thunder hear- or sound as when winds whirl
With lashings and do buffet about in air
A hanging cloth and flying paper-sheets.
For sometimes, too, it chances that the clouds
Cannot together crash head-on, but rather
Move side-wise and with motions contrary
Graze each the other's body without speed,
From whence that dry sound grateth on our ears,
So long drawn-out, until the clouds have passed
From out their close positions.
And, again,
In following wise all things seem oft to quake
At shock of heavy thunder, and mightiest walls
Of the wide reaches of the upper world
There on the instant to have sprung apart,
Riven asunder, what time a gathered blast
Of the fierce hurricane hath all at once
Twisted its way into a mass of clouds,
And, there enclosed, ever more and more
Compelleth by its spinning whirl the cloud
To grow all hollow with a thickened crust
Surrounding; for thereafter, when the force
And the keen onset of the wind have weakened
That crust, lo, then the cloud, to-split in twain,
Gives forth a hideous crash with bang and boom.
No marvel this; since oft a bladder small,
Filled up with air, will, when of sudden burst,
Give forth a like large sound.
There's reason, too,
Why clouds make sounds, as through them blow the winds:
We see, borne down the sky, oft shapes of clouds
Rough-edged or branched many forky ways;
And 'tis the same, as when the sudden flaws
Of northwest wind through the dense forest blow,
Making the leaves to sough and limbs to crash.
It happens too at times that roused force
Of the fierce hurricane to-rends the cloud,
Breaking right through it by a front assault;
For what a blast of wind may do up there
Is manifest from facts when here on earth
A blast more gentle yet uptwists tall trees
And sucks them madly from their deepest roots.
Besides, among the clouds are waves, and these
Give, as they roughly break, a rumbling roar;
As when along deep streams or the great sea
Breaks the loud surf. It happens, too, whenever
Out from one cloud into another falls
The fiery energy of thunderbolt,
That straightaway the cloud, if full of wet,
Extinguishes the fire with mighty noise;
As iron, white from the hot furnaces,
Sizzles, when speedily we've plunged its glow
Down the cold water. Further, if a cloud
More dry receive the fire, 'twill suddenly
Kindle to flame and burn with monstrous sound,
As if a flame with whirl of winds should range
Along the laurel-tressed mountains far,
Upburning with its vast assault those trees;
Nor is there aught that in the crackling flame
Consumes with sound more terrible to man
Than Delphic laurel of Apollo lord.
Oft, too, the multitudinous crash of ice
And down-pour of swift hail gives forth a sound
Among the mighty clouds on high; for when
The wind hath packed them close, each mountain mass
Of rain-cloud, there congealed utterly
And mixed with hail-stones, breaks and booms...

Likewise, it lightens, when the clouds have struck,
By their collision, forth the seeds of fire:
As if a stone should smite a stone or steel,
For light then too leaps forth and fire then scatters
The shining sparks. But with our ears we get
The thunder after eyes behold the flash,
Because forever things arrive the ears
More tardily than the eyes- as thou mayst see
From this example too: when markest thou
Some man far yonder felling a great tree
With double-edged ax, it comes to pass
Thine eye beholds the swinging stroke before
The blow gives forth a sound athrough thine ears:
Thus also we behold the flashing ere
We hear the thunder, which discharged is
At same time with the fire and by same cause,
Born of the same collision.
In following wise
The clouds suffuse with leaping light the lands,
And the storm flashes with tremulous elan:
When the wind hath invaded a cloud, and, whirling there,
Hath wrought (as I have shown above) the cloud
Into a hollow with a thickened crust,
It becomes hot of own velocity:
Just as thou seest how motion will o'erheat
And set ablaze all objects- verily
A leaden ball, hurtling through length of space,
Even melts. Therefore, when this same wind a-fire
Hath split black cloud, it scatters the fire-seeds,
Which, so to say, have been pressed out by force
Of sudden from the cloud- and these do make
The pulsing flashes of flame; thence followeth
The detonation which attacks our ears
More tardily than aught which comes along
Unto the sight of eyeballs. This takes place-
As know thou mayst- at times when clouds are dense
And one upon the other piled aloft
With wonderful upheavings- nor be thou
Deceived because we see how broad their base
From underneath, and not how high they tower.
For make thine observations at a time
When winds shall bear athwart the horizon's blue
Clouds like to mountain-ranges moving on,
Or when about the sides of mighty peaks
Thou seest them one upon the other massed
And burdening downward, anchored in high repose,
With the winds sepulchred on all sides round:
Then canst thou know their mighty masses, then
Canst view their caverns, as if builded there
Of beetling crags; which, when the hurricanes
In gathered storm have filled utterly,
Then, prisoned in clouds, they rave around
With mighty roarings, and within those dens
Bluster like savage beasts, and now from here,
And now from there, send growlings through the clouds,
And seeking an outlet, whirl themselves about,
And roll from 'mid the clouds the seeds of fire,
And heap them multitudinously there,
And in the hollow furnaces within
Wheel flame around, until from bursted cloud
In forky flashes they have gleamed forth.

Again, from following cause it comes to pass
That yon swift golden hue of liquid fire
Darts downward to the earth: because the clouds
Themselves must hold abundant seeds of fire;
For, when they be without all moisture, then
They be for most part of a flamy hue
And a resplendent. And, indeed, they must
Even from the light of sun unto themselves
Take multitudinous seeds, and so perforce
Redden and pour their bright fires all abroad.
And therefore, when the wind hath driven and thrust,
Hath forced and squeezed into one spot these clouds,
They pour abroad the seeds of fire pressed out,
Which make to flash these colours of the flame.
Likewise, it lightens also when the clouds
Grow rare and thin along the sky; for, when
The wind with gentle touch unravels them
And breaketh asunder as they move, those seeds
Which make the lightnings must by nature fall;
At such an hour the horizon lightens round
Without the hideous terror of dread noise
And skiey uproar.
To proceed apace,
What sort of nature thunderbolts posses
Is by their strokes made manifest