Page:The Natural History of Pliny.djvu/104

 70 plii^t's katural histobt. [Book II. duced by the 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 the 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*