70 plii^t's katural histobt. [Book II. 



duced by tlie stroke given to the condensed air, and hence 

 it is that the fire darts from the chinks of the clouds. It is 

 possible also that the vapour, which has risen from the earth, 

 being repelled by the stars, may produce thunder, when it is 

 pent up in a cloud ; nature restraining the sound whilst the 

 vapour is struggling to escape, but when it does escape, the 

 sound bursting forth, as is the case with bladders that are 

 distended with air. It is possible also that the spirit, what- 

 ever it be, may be kindled by friction, when it is so violently 

 projected. It is possible that, by the dashing of the two 

 clouds, the lightning may flash out, as is the case when two 

 stones are struck against each other. But all these things 

 appear to be casual. Hence there are thunderbolts which 

 produce no effect, and proceed from no immediate actual 

 cause ; by these mountains and seas are struck, and no in- 

 jury is done. Those which prognosticate future events pro- 

 ceed fi^m on high and from stated causes, and they come 

 from their peculiar stars \ 



CHAP. 44. — THE ORIGIN OF WINDS. 



In like manner I would not deny that winds, or rather 

 sudden gusts, are produced by the arid and dry vapours of 

 the earth ; that air may also be exhaled from water, which 

 can neither be condensed into a mist, nor compressed into a 

 cloud ; that it may be also driven forward by the impulse of 

 the sun, since by the term ' wind' we mean nothing more than 

 a current of air, by whatever means it may be produced^. 

 !Por we observe winds to proceed from rivers and bays, and 

 from the sea, even when it is tranquil ; while others, which 

 are named Altani, rise up from the earth ; when they come 

 back from the sea they are named Tropcdi, but if they go 

 straight on, Apogcei^. 



^ " Prsesertim ex tribus superioribus planetis, uti dictum est, cap. 18." 

 nardouin, in Lemaire, i. 322. 



2 Our author's opinion respecting tlie origin of winds nearly agrees 

 with that of Aristotle ; " nihil ut ahud ventus (dvefios) sit, nisi aer multus 

 fluctuans et compressus, qui etiam spiritus {Trvevfxa) appellatur;" De 

 Meteor. This treatise contains a full account of the phsenomena of 

 winds. Seneca also remarks, " Yentus est aer fluens ; " Nat. Qusest. lib. 3 

 &5. 



• Ai'istotle informs us, that the winds termed apogaei (airoyaioi) pro* 



