f 52 ] 
which is extinguish’d as foon as it is thrufl into the* 
vapour. I made the experiment Several times my- 
felf, and I always faw the flame perifh without 
noife, without that fort of hiding, which is heard 
when an ‘ignited body is quenched in water, or any 
other fubflance that contains a great deal. In exa.- 
mining this phenomenon, I dil'covered another not 
lefs curious. The thick Smoke, which appeared 
immediately after the extinction of the flambeau, re- 
mained floating on the vapour ; and, being lighter 
than it, but heavier than the air above it, it Spread 
between both, and moving outward flowly at firft, 
and afterwards quicker, becaufe the Hope grew 
greater, it plainly indicated the motion and direction 
of the fluid, that carried it along. 
If any one ask, why this Smoke did not afeend into 
the air that was over it, and whence proceeded that 
degree of gravity fo unufual to Smoke ? my anfwer is, 
that probably it proceeded from the vapour, in which 
the dame had been Smothered. One may imagine, 
that thefe two fluids, being better adapted to mix 
with one another than with the air, were blended to- 
gether towards the Surface of the vapour ; and that 
the fmoke, tho’ dill the lighter of the two, retained 
weight enough to remain floating under the Surface 
of the air. 
The vapour of the grotto is not the only one, 
that has been Seen moving thus under the air, and 
Spreading from its Source into lower places. After 
great eruptions of Vefuvius, the ditches, cellars, 
cifterns, and wells, in the neighbourhood of the 
volcano, and chiefly near the places where the lavas 
flopped, are Sometimes found full of a Sort of 
