On the Nature of the Universe (Oxford World’s Classics) (49 page)

Driven through the sky, just as, we may be sure,

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When the strong blasts of the north-west wind

Blow through a wood, leaves rustle and branches crack.

Sometimes also a furious force of wind

Shears through a cloud head on and splits it up.

For what the blast can do there, we can tell

From our own experience, seeing that here on earth,

Where it is gentler, none the less tall trees

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It overturns and tears up from the roots.

And there are waves among the clouds, which make

A kind of low roar as they break, as happens

Likewise in deep rivers and when the sea

Breaks with its rolling tide upon the shore.

Thunder comes also when a flaming stroke

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Of lightning falls from a cloud upon a cloud.

If the receiving cloud is full of water

It makes a great noise quenching it at once,

As red-hot iron taken from the furnace

Hisses when plunged into a tank of water.

And if a drier cloud receives the fire

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It lights at once and burns with mighty roar,

As on the mountains crowned with laurel came

A flame that driven by a whirling wind

Burnt all the woodlands with its rushing fire.

No other thing than Phoebus’ Delphic laurel

Burns with such fearful sound and crackling flame.

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Lastly, the crack of ice and fall of hail

Oft makes a noise in the great clouds on high.

For the great mountains of the thunderclouds

Are broken, pressed together by the wind,

And crushed into a narrow space, and mixed with hail.

Lightning occurs likewise when clouds colliding

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Have struck out many seeds of fire, as stone

Strikes stone or iron; then also light leaps out

When stone is struck and scatters sparks of fire.

Our ears receive the sound of thunder later

Than our eyes see the lightning, for this reason;

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Things always come more slowly to the ears

Than to the eyes; as this example shows:

If in the distance you observe a man

Felling a tall tree with twin-bladed axe

You see the stroke before the sound of it

Reaches your ears; so also we see lightning

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Before we hear the thunder, which is produced

At the same time as the fire, and by the same cause,

Born of the same collision of the clouds.

Here is another way in which the clouds

Bathe all the landscape in a fleeting light

As the storm flashes with its quivering stroke.

When wind has entered a cloud and whirling round

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Has made the cloud condense around the hollow,

As I explained before, it becomes hot

With its own motion, as you see everything

Grows burning hot with motion; leaden bullets

Melt as they spin in a long flight through the air.

So when the black cloud by the burning wind

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Has been split up, the sudden violent pressure

Makes it shoot out the seeds of heat, and these

Produce the winking flashes of bright flame.

Then the sound follows, coming to the ears

More slowly than the light comes to our eyes.

This happens, you must understand, when clouds are thick

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And are piled high, one cloud upon another,

By an amazing force. Don’t be misled

Because observing from below we see

More easily their wide expanse spread out

Than the great mighty mass piled high above.

Take note then, when you see clouds like mountains

Carried before the winds across the sky,

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Or when you see them on the mountain tops

Piled high, one on another, pressing down

And lying still, with all the winds at rest,

Then you will recognize their mighty mass,

And see great caverns fashioned in them

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With beetling crags, and when a storm builds up

Winds fill them, and imprisoned in the clouds

They vent their indignation with a roar,

And growl like angry beasts shut up in cages;

This way and that they fill the clouds with din,

And circle round and round trying to escape;

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They roll the seeds of fire out of the clouds

And mass them together, and in the hollow furnace

They spin a circling flame, until at last

They burst the cloud, and blaze into the sky.

And also there’s another reason why

That rushing golden gleam of liquid fire

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Darts down to earth. It is that the clouds themselves

Must contain very many seeds of fire.

For when they are entirely free of moisture

Mostly their colour is flaming and shining bright.

Indeed from the sun’s light they must receive

Many such seeds, so with good cause they blush

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And pour out fires. These therefore, when the wind

Has driven them together and compressed them,

Squeeze out and then eject the seeds of fire

Which make the colours of the lightning-flash.

Lightning occurs also when in the sky

The clouds are thinning out, for when the wind

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Gently disperses them as they move on

And dissolves them, then the seeds that make the lightning

Must fall perforce; but then the lightning comes

Noiseless, and without the hideous crash and terror.

I now discuss the nature of thunderbolts.

This the strokes show, and branding marks of heat,

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And the holes breathing noxious fumes of sulphur.

These are the marks of fire, not wind or rain.

Besides, they often set roofs alight, and flame

Gains quick dominion all inside the houses.

This fire, my friend, the thinnest of all fires,

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Nature has made of atoms so small and swift

That nothing in the world can stand against it.

The thunderbolt passes through walls of buildings

As sounds and voices do, through stone, through bronze,

And in an instant melts both bronze and gold.

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And wine inside a vessel suddenly

It makes evaporate, though the jar remains intact;

Doubtless because, as the heat reaches it,

It loosens the fabric of the earthenware

And makes it porous, then entering the jar

It quickly dissolves the atoms of wine and scatters them.

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And this we see the sun can never do

In an age, however strong its flashing heat.

So much more mobile and more masterful

Is the strong power of the thunderbolt.

And now, how they are made and have such power

That with a stroke they can split towers asunder,

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Overturn houses, tear out beams and rafters,

Move monuments of men, struck down and shattered,

Rob human beings of life and slaughter cattle,

And all else of this kind, by what strange power

They work, I’ll tell, and delay you no more with promises.

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We must believe that thunderbolts are made

From thick clouds piled up high; they never strike

From a clear sky or thin layer of cloud.

The facts themselves make clear without a doubt

That at a time of thunderstorms clouds mass together

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Everywhere through the air, so that we think

That all the darkness out of Acheron

Has filled the mighty caverns of the sky.

So dark, beneath the hideous night of cloud,

The face of fear hangs over us above,

When storm begins to forge the thunderbolts.

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And very often too across the sea

A black cloud falls, like pitch poured from the sky,

Loaded with darkness from afar, and draws with it

A black storm big with thunderbolts and blasts

Filled to the brim itself with wind and fire,

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So that on land also men shiver and seek shelter.

From this we must infer that thunderstorms

Stretch high above our heads. For so much blackness

Could never overwhelm the earth unless

A multitude of clouds piled high on clouds

Built up above us, blotting out the sun.

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Nor could there fall that torrent of the rain

That makes the rivers flood and drowns the fields

If ether were not full of clouds piled high.