How, some one further inquires, are those bright gleams of light 1 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 2 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 3 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 _astrapoplecta_[32] (= star-struck). Those that have a longer career and a stronger fire 4 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 5 fire, since their immense orb sometimes surpasses in size that of the morning sun. [32] The term might also mean _struck by lightning_. A commoner reading gives the meaning: which, when grazed by this means, the Greeks called plecta (= struck).