PU NON TENER 
Profefor WirriAaMs, on Earthquakes. 291^ 
vapour, when its motion is confined and directed by a particu- 
lar channel or paffage, we may learn from that of a blazing 
chimney. The aétion of fire, when turning the inflammable 
materials, with which the chimney abounds, into flame and 
vapour, produceth a noife or roar of a very particular kind ; and 
which feems to be different from almoft any other : and there 
_ is nothing to which the report of our earthquakes is more fimi- 
lar, or has been more often compared. 
There is alfo an apparent agreement between the effets cx a 
fabterraneous vapour, and the 4/»d and motion of the fhocks. 
When the materials, from which a fubterraneous vapour is pro- 
duced, lie promifcuoufly mingled and blended together, the 
effet of an explofion would be a violent ebullition, or blaft 
upwards ; tearing and rending a circle of earth, all around. 
This feems to have been the cafe in the earthquakes of Sicily, 
Lima and Samaica. * When the vapours can have a regular dif- 
charge through any aperture in the furface of the earth, they 
will vent themfelves in copious effufions and exhalations, and 
thus fpend their force this way, as they gather aid from : 
time to time. Thus it has bæn, with Hecla. formerly ; and 
with: Fe "efuoius, ZEtna, and other 
the vapours are confined under the furface of the Eh; and' 
have fübterraneous paflages, or proper ftrata, for them to run i in, 
by the violence of their expanfion, they will heave up the fit- 
face of the earth, and thus caufe, not an inftantaneous con- 
cufiion, but a progreflive fwell or undulation of thé darth == 
And this will be continued till the vapours, thus confined, find ; 
or force for. themfelves a paffage, where. they may burft from — 
their caverns, and difcharge themíelves into the open | air— 
Nn 2 pens 
core i amr ST e 
