Heraclitus is of opinion that the flash of lightning is the first 1 attempt of a fire to kindle; just as on earth when the flame is at first unsteady, now dying down and now darting up again. The ancients used to call this summer lightning. We now say in the plural thunder peals (_tonitrua_); the ancients said either thunder (_tonitruum_, sing.) or merely peal (noise, _tonus_). The foregoing remark I 2 find in Caecina, an eloquent man, who would have had a considerable reputation as such had he not been overshadowed by Cicero’s towering form. Besides, the ancients had other variants of a similar kind. They employed with the penult short the word that we use with it long; we say _fulgēre_ (to lighten) just as we do _splendēre_ (to gleam). But in order to denote this sudden burst of light from the clouds their usage was to shorten the middle syllable so as to make it _fulgěre_. LVII What do I think myself about the matter, you ask. For up to this 1 point I have been reproducing the opinions of others. Well, I will tell you. There is lightning when light bursts out suddenly and widely. This occurs when the atmosphere has been changed, by the rarefaction of the clouds, into fire, which has not gathered strength to issue to any considerable distance. There is, I presume, no cause for surprise either that movement rarefies air or that rarefaction kindles fire. In the same way a leaden bullet is liquefied when discharged from a sling, and falls in drops by reason of atmospheric friction just as it would do through fire. Bolts of lightning are more numerous in 2 summer, for the reason that there is most heat at that season. Fire naturally starts more readily when the friction is in warmer air. A flash of lightning which merely gleams and a bolt which is discharged are produced in exactly the same way. But there is less force in the former case and less fuel. To put my opinion on the point shortly: a bolt is just lightning in its most intense form. So then, when a body 3 of the nature of heat or smoke is exhaled from the earth and, meeting with clouds, is for a long time rolled about in their hollows, at last it bursts out. Since it possesses no strength, it is merely a flash. But when lightnings have more material and burn with fiercer glow, they not merely become visible, but also fall to the earth. LVIII