[ 5i 3 
tliis experiment, the heat of the exterior air Was 
hardly 18 degrees. 
I went out of the grotto, and having kneeled down 
at fome few fteps diftance below the entrance, in 
order to examine the vapour a fecond time, I ob- 
ferved its waving motions under the air, better than 
the firft time ; becaufe now both thefe fluids had 
been put in agitation juft before. I had fcarcely 
been fome moments in this pofture, when I felt in 
my legs and left-hand, which I had laid on the 
ground to fupport me, a heat like that, which I had 
remark’d in the grotto, but weaker. I retir’d a lit- 
tle tideways, bowing down my head fo as to view 
the furface of the earth almoft horizontally, and very 
diflinCtly faw a vapour fimilar to that of the grotto, 
but not rifing fo high, and feeming to glide along, 
and follow the flope of the ground. 
Hence I conjectur’d, that this fluid, too heavy to 
rife more than five or fix inches, without being con- 
fined on every fide, fpread itfelf from the cavern, 
where its fource lay, into the places below it ; and 
that it was difiipated there, either by being divided 
into a large fpace, or by yielding to the agitations of 
the air. I imagined further, that the ground adja- 
cent to the grotto might poflibly exhale this fluid, 
which I perceived, as well as the grotto itfelf, only 
With the difference of more or lefs. The warmth, 
which I felt in my hand, while I kept it on the 
ground, render’d the laft of thefe conjectures very 
probable ; and the firft was converted into certainty 
by the following experiment. 
It is a conftant cuflom to entertain the curious, 
who vifit the grotto, with a well-lighted flambeau, 
G % which 
