BOOK II. XLIII. II2-XLIV. 114 



smoke whirls up. And I agree that these produce 

 storms, and if there is wind or steam struggling in 

 the cloud, it gives out claps of thunder, if it bursts 

 out on fire, flashes of hghtning, if it forces its way on 

 a longer track, heat-hghtning. The latter cleaves 

 the cloud, the flashes burst through it, and thunder- 

 claps are the blows of the fires colhding, causing 

 fiery cracks at once to flash out in the clouds. It is 

 also possible for breath emerging from the earth, 

 when pressed down by the counter-impact of the 

 stars, to be checked by a cloud and so cause thunder, 

 nature choking down the sound while the struggle 

 goes on but the crash sounding when the breath 

 bursts out, as when a skin is stretched by being 

 blown into. It is also possible for this breath, what- 

 ever it is, to be set on fire by the friction during its 

 headlong progress. It is also possible for it to be 

 struck out by the impact of the clouds, as by that of 

 two stones, with heat-lightning flashing out hke sparks. 

 But all these occurrences are accidental — they cause 

 mere senseless and inefFectual thunder-claps, as their 

 coming obeys no principle of nature — they merely 

 eleave mountains and seas, and aU their other blows 

 are ineffectual ; but the former " are prophetical 

 and sent from on high, they come by fixed causes and 

 from their own stars. 



XLIV. Similai-ly I am not prepared to deny that Aircurrem 

 it is possible for winds or rather gusts of air to be '^^nlouroj 

 produced also by a dry and parched breath from the ^f^ eanh. 

 earth, and also possible when bodies of water breathe 

 out a vapour that is neither condensed into mist or 

 sohdified into clouds ; and also they may be caused 

 by the driving force of the sun, because wind is 

 understood to be nothing else than a wave of air; 



255 



