PHYSICAL SCIENCE 



LVI 



1 HERACLITUS is of opinion that the flash of lightning 

 is the first 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 (toni- 

 trua) ; the ancients said either thunder (tonitruum, 



2 sing.) or merely peal (noise, tonus]. The fore- 

 going remark I 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 

 fulgere (to lighten) just as we do splendere (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 fulgere. 



LVII 



WHAT do I think myself about the matter, you ask. 

 For up to this 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 



