[ 611 1 
chiefly to expefl in the moft mountainous countries, 
according to the idea before given of them *. 
72.^ To make this fomething clearer, let us fup- 
pofe, in Fig. 1. the vapour to be palling between 
the ftrata in the dotted line C, and to go forwards, 
till it ai lives at A : whilA, then, it palles under the 
deeper parts at E, it will raife the earth over it but 
little, as well becaule it will be fpread broader and 
thinner, as becaufe it will be more comprelfed by the 
weight of the fuperincumbent matter; but as it ar- 
rives towards A, not only the latter part will be 
driven forwards with greater velocity, but the fore- 
nooft will travel ilower, on account of its travelling 
under a f thinner fet of ftrata ; and, befides this, the 
load being much lefs, it will greatly expand itfelf. 
Fiom all thefe caufes taken together, the wave at the 
iuiface of the earth, occafioned by the palling of the 
vapour under it, will not only be much higher, but 
alfo much Ihorter, and, confequently, the fides of it, 
on both thefe accounts, will be much more inclined 
to the honzon . and, moreover, becaule the pro°refs 
of the wave will be flower, it will give more time to 
any waters fituated on one fide of it, to flow one 
way ; and on this account alfo, the apparent agitation 
of them will be increafed. 
\ 
Sect. II. 
73* We are told, that, in the Lilbon earthquake 
of 1757, “ the bar [at the mouth of the Tagus] was 
“ feen dry from fhore to fhore ; then fuddenly the fea. 
* See art. 43. 
f See art. 63. the note. 
Vol. LI, 
tc 
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