Chap. 52.] IIGHTimTG AITD ITS ErFECTS. 8L 



diiFerent causes ; the air, which is condensed in the winter, 

 is made still more dense by a thicker covering of clouds, 

 while the exhalations from the earth, being all of them rigid 

 and frozen, extinguish whatever fieiy vapour it may receive. 

 It is this cause which exempts Scythia and the cold districts 

 round it from thunder. On the other hand, the excessive 

 heat exempts Egypt ; the warm and dry vapours of the earth 

 being very seldom condensed, and that only into light clouds. 

 But, in the spring and autumn, thunder is more frequent, 

 the causes which produce summer and winter being, in each 

 season, less efficient. From this cause thunder is more fre- 

 quent in Italy, the air being more easily set in motion, in 

 consequence of a milder winter and a showery summer, so 

 that it may be said to be always spring or autumn. Also in 

 those parts of Italy which recede from the north and lie to- 

 wards the south, as in the district round our city, and in 

 Campania, it lightens equally both in winter and in summer, 

 which is not the case in other situations. 



CHAP. 52. (51.) — OP THE DITFEHEirT KINDS OF LIGHTNIKO^ 

 AND THEIB WONDERFUL EFFECTS. 



"Wehaveaccountsof many different kinds of thunder-storms. 

 Those which are dry do not bum objects, but dissipate them ; 

 while those which are moist do not bum, but blacken them. 

 There is a third kind, which is called bright lightning^, of a 

 very wonderful nature, by which casks are emptied, without 

 the vessels themselves being injured, or there being any other 

 trace left of their operation^. Gold, copper, and silver are 

 melted, while the bags which contain them are not in the 

 least burned, nor even the wax seal much defaced. Marcia, 

 a lady of high rank at Rome, was struck while pregnant ; 

 the foetus was destroyed, while she herself survived without 



^ " fulgiir." The account of the different kinds of thimder seems to 

 be principally taken from Aristotle ; Meteor, iii. 1. Some of the phfie- 

 nomena mentioned below, which would naturallv appear to the ancients 

 the most remarkable, are easily explained by a reference to their electrical 

 origin. 2 « quod clarum vocant." 



3 This accoimt seems to be taken from Aristotle, Meteor, iii. 1. p. 574 ; 

 see also Seneca, Nat. Qusest. ii. 31. p. 711. We have an account of the 

 pecuhar effects of thimder in Lucretius, vi. 227 et seq. 



VOL. I. 



