Fulgit item, nubes ignis cum semina multa
excussere suo concursu, ceu lapidem si
percutiat lapis aut ferrum; nam tum quoque lumen
exsilit et claras scintillas dissipat ignis.
sed tonitrum fit uti post auribus accipiamus,
fulgere quam cernant oculi, quia semper ad aures
tardius adveniunt quam visum quae moveant res.
id licet hinc etiam cognoscere: caedere si quem
ancipiti videas ferro procul arboris auctum,
ante fit ut cernas ictum quam plaga per aures
det sonitum; sic fulgorem quoque cernimus ante
quam tonitrum accipimus, pariter qui mittitur igni
e simili causa, concursu natus eodem.
(Lucretius, De Rerum Natura 6.160-172)
It lightens also, when clouds by their collision have struck out many seeds of fire; as if stone or steel should strike stone, for then also a light leaps forth scattering abroad bright sparks of fire. But the reason why we hear the thunder after the eyes see the lightning is that things always take longer to reach the ears than to produce vision. The truth of this you may understand from another experience: if you should see someone at a distance cutting down a well-grown tree with a double-headed axe, you see the stroke before its thud sounds in your ears; so also we see lightning before we hear the thunder, which is produced at the same time and by the same cause as the fire and born of the same collision. (tr. William Henry Denham Rouse, revised by Martin F. Smith)