Chftp. 52.] LiaHTKING AND ITS EPFECTS. 81 
different causes ; tlie air, whicL 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 fiery 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 vdnter 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.) — or THE DIEEEBEFT KIIS^DS OP LIGHTKII^a^ 
AND THEIR WOraEEEUL EEEECTS. 
Wehaveaccountsof many different kinds of thunder-storms. 
Those which are dry do not burn objects, but dissipate them ; 
while those which are moist do not burn, 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^. Grold, 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 Kome, w^as struck while pregnant ; 
the foetus was destroyed, while she herself survived without 
^ " falgiir." The account of the different kinds of thunder seems to 
be principally taken from Aristotle ; Meteor, iii. 1. Some of the phse- 
nomena mentioned below, which would naturally appear to the ancients 
the most remarkable, are easily explained by a reference to their electrical 
origin. 2 « quod clarimi vocant." 
3 This account seems to be taken from Aristotle, Meteor, iii. 1. p. 574 ; 
see also Seneca, Nat. Qu£est. ii. 31. p. Vll. We have an accomit of the 
pecuhar effects of thunder in Lucretius, vi. 227 et seq^. 
YOL, I. G 
