r 595 ] 
56. Both the tremulous and wave-like motion ob- 
ieived in eaithcjuakes, may be very well accounted 
for 
“ heat ofr th e metal of the firft gun drove fo much damp into the 
mould of the iecond, whicn was near it, that as foon as the 
metal was Jet into it, it blew up with the greateft violence, tear- 
“ ing up the ground fome feet deep, breaking down the furnace, 
“ untiling the hoiffe, killing many fpedtators on the fpot, with the 
ftreams 01 melted metal, and fealding many ethers in a moft mi- 
“ ferab,e manner.” [See the note at the end of procefs 44th of the 
Englifh tranflation of Cramer’s Art of aflaying Metals.]' 
Other inftances of the violence of vapours raifed from water, are 
frequently to be met with : one of Papin’s digefters being placed 
between the bars of a grate, where there was a fire, was, after 
fome time, burft by the violence of the fleam, the fire was all 
blown out of the grate, and a piece of the digefter was driven 
againft the leaf of a flrong oak table, which it broke to pieces. 
[See Philof. Tranf. N 454 ’ or Martyn’s Abr. vol. viii. p. 465.] 
The marquis of W orcefter alfo, in his Century' of Inventions, tells 
us, that he burft a cannon by the fame means. 
It has been fometimes imagined, that the vapours, which occa- 
fion earthquakes, were of the fame kind with thofe fulminating 
damps, of which we often meet with inftances in coal mines! 
I\ow, there are feveral things which make it very probable, that 
this is not the cafe . it is true, the force of fuch vapours is very 
great; we have had inftances, where large beams of timber have 
been thrown to the diftance of an hundred yards by them : [fee 
Pnilof. Tranf. N° 136* or vol. ii. p. 381. Lowthorp’s Abr.] but 
what is this to the force of that vapour, which could throw ftones 
of twenty or thirty ton weight to the diftance of three leaoues? 
Nor, indeed, is it at all probable, that any vapour, already in the 
form of a vapour, can, by fuddenly taking fire, increafe its dimen- 
110ns fo much, as to produce that immenfe quantity of motion, 
which we obferve in fome earthquakes ; but this is rather to be 
expedted from fome folid body, fuch as water, which is capable of 
being converted, and that almoft inftantly, into one of the lighteft, 
and perhaps one of the moil elaftic, vapours in the world. Air* 
when heated to the greateft degree that it is capable of receiving 
from the hotteft fires we can make, acquires a degree of elafticity 
about five times as great as that of common air; the vapour of 
Vol. LI. 4 H „„„ 
