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How, some one further inquires, are those bright gleams of light which the Greeks call Sela (luminosities) produced? In many ways, people say. They may arise from the violence of the winds, or from the fervent heat of the upper heavens. Fire is a very widely diffused element there, and sometimes catches the lower regions if they are combustible. The mere motion of the stars in their courses may kindle fire, and convey it to all that lies beneath them. Nay, is it not quite possible that the atmosphere should drive up even to the ether the germs of fire, from which may arise a glow or burning or darting resembling a star? Some of these gleams rush headlong like shooting stars, some remain fixed in their place, emitting light sufficient to dispel darkness and reinstate daylight, until their fuel is used up, and they gradually grow dimmer, and by and by, just like a flame which is dying out, are by gradual subsidence reduced to nothingness. Some of these appear in the clouds, some above them: in such cases the thick air nearer the earth feeds them for a long time, but eventually forces them right up to the stars. Certain of these last no considerable time: they straightway dart across the sky, or are extinguished just at their point of origin. These are called gleams because their appearance is fitful and short-lived, though their fall is not always unattended by injury: they have often caused as much damage as lightning. One has seen houses struck by them, what the Greeks call astrapoplecta32 (= star-struck). Those that have a longer career and a stronger fire which follows the motion of the heavens, or those that pursue an orbit of their own, are regarded by the Stoic philosophers as Comets: of which more anon. Different kinds of these are pogoniae (bearded), lampades (torches), and cyparissiae (like cypress trees), and all the rest of them: they have a thin tail of fire. It is doubtful whether beams (trabes) and the rare barrel-meteors (pithitae) should be placed in this category or not. Such meteors require a great mass of fire, since their immense orb sometimes surpasses in size that of the morning sun.
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Among these should certainly be placed a phenomenon of which we often read in the chronicles—the heavens appeared to be on fire. The blaze of it is occasionally so high as to mount to the very stars; occasionally it is so low as to present the appearance of a distant fire. In the reign of Tiberius Caesar the fire brigade hurried off to the relief of the colony at Ostia, supposing it to be in flames; during the greater part of the night there had been a dull glow in the sky, which appeared to proceed from a thick smoky fire. No one has any doubt that these burnings in the heavens contain flame as really as they display it: they have a certain substance in them. As to those formerly discussed, I mean rainbows and halos, it is a question whether they deceive the sight and consist of an illusion; or really contain what appears in them. I and those who think with me cannot convince ourselves that the rainbow and halo have a basis of any definite material in them. For we judge that in a mirror there is nothing but a deception: the mirror only pretends to show a foreign body. What is revealed does not exist in the mirror. Otherwise it would not come out of it, nor would it be forthwith obscured by another image: nor would innumerable forms now fade from it, now be received by it. What follows, then? That these are mere phantoms and the insubstantial imitation of real bodies. Indeed, in certain instances, people have so arranged mirrors that the objects have been distorted and degraded in the reflection. For, as I have already said, there are some mirrors that twist the faces of those who look into them, some that enormously increase them until they exceed all size and proportions of these bodies of ours.