Physical Science in the Time of Nero

XX

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Most of our Stoic brethren entertain another view, which they do not regard as inconsistent with fact. Let me explain it. We observe many species of fire engendered on high, now the heavens ablaze, now

Long glistening trains of flame behind,

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now huge torches of fire being hurried along. The lightning itself, whose velocity is so marvellous that it at once blinds, and at the same instant restores, the sight, is fire arising from the friction of air that suffers more violent internal pressure than usual. That is why it does not remain long, but glides off once it issues from the cloud, forthwith perishing. But other fiery appearances remain for a considerable time, and do not break up until all the fuel on which they fed has been used up. Here belong the strange sights recorded by Posidonius—pillars and shields all ablaze, and other flames of marvellous strangeness. They would attract no attention if they ran their course after customary laws; but now the sight of them sends all men agape. They bring down sudden fire from the heights of heaven, sometimes producing a flash which is gone in a moment, sometimes compressing the air, which is forced into a glow; it is a miracle all the same. Yes, and is not sometimes a gulf opened in the ether, which seems to retire on all sides, with a great glare of light in the hollow centre? You are ready to cry out. What is this?

... I see the very centre of heaven open,
And the stars wandering in the sky....

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These stars sometimes do not wait for night to show their light, but burst out in the full light of day. The reason, however, for the stars showing at a time not their own is different from that alleged; it is well known that they are there all the time, though hidden. Many comets, too, we cannot see because they are obscured by the sun’s rays. Posidonius, in fact, tells us that during an eclipse of the sun a comet once appeared which the sun’s proximity had hitherto concealed. Often, when the sun has just set, straggling fires‍96 are seen close to him. No doubt the nucleus of the comet is bathed in sunlight, and therefore cannot be discerned; but the tail escapes the effect of the sun’s rays.