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 comes 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 north-west 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...
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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:
