236 Dr. Thompfon, of Naples, 
to this reflection, when I confefs that I 
have been aftonifhed at my own blindnefs 
much more than at the omiffion of others, 
having myfelf already more than once ex- 
amined the Zolfatara, without having 
been arrefted for a moment by the above- 
recited phenomenon, which would appear 
impoffible, fince it prefents itfelf under fo 
many points of view. Let another na- 
tural philofopher anfwer for me: 
s¢ Hec fi pernofces, parva perfunétus opella, 
(Namque aliud ex alio clarefcet) non tibi 
ceca 
Nox iter eripiet, quin ultima naturai 
Pervideas, ita res accendunt lumina rebus!”" 
Lucret. lib i. 
(8) In July of the prefent year, coaft- 
ing the edge of the yait cleft, whence was 
vomited the immenfe lava, which the laft 
year ruined, ina few hours, the populous 
town, Torre del Greco, I remarked there 
the volcanic fand, partly red, partly 
green ¢fhorl), as though it had been pow- 
dered with hoar froft, which, to the eye: 
would have appeared a faline fubftance ; 
but this likewife is nothtng elfe than a 
moft fubtle plaifter, or filiceous varnifh, 
_ which covers over this fand, whofe pro- 
minent grains inclining toa circular form, 
have the appearance of fo many little 
pearls. This fubtle and tender cruft, 
on the application of water, becomes 
hydrophanous and tranfparent, wience 
the eye, although experienced,  eafily 
pafles it unobferved. The fand, con- 
gilutinated in part by thofe incruftations, 
and in part by its calx of iron, forms a 
kind of fuperficial mirror of little confift- 
ency upon the afhes. In other places 
around the new openings of the mountain, 
a fimilar eruft is found, lefs bright, but 
thicker, which affumes the form of fta- 
JaQtites, and recruits itfelf with the 
iarger. volcanic fragments: It is ob- 
fervable, that in ali thefe places, open- 
ings, from whence efeape humid and 
fcalding vapours, are frequent even at 
prefent. : 
(8) Returning into Hchia in Auguft 
of the prefent year, and invited to vilit 
ecrtain outlets of hot vapour, and as I 
was affured, of hepatic air, I conceived 
from hence the poffibility of finding there 
alfe, fulphur, which might tend to elu- 
cidate the generation of that fulphur 
found by Abbate Breiilak (f. 6.) in a 
place where the vapours no longer exift. 
The prefenee of filiceous incruftations, 
together with the fulphur already men- 
tioned (fo-6.),0 would’ likewife deferve 
. fome confideration, ‘as thefe had all the 
eharaéter of being produced at the fame. 
a 
on Siliceous Incruftations. 
time as the fulphur. I went, therefore, 
in company with Count Redern, to a 
place called Monticeto, above Cafamic. 
ciola, and there on the fide of a channel 
produced by torrents, but then dry, we 
met indeed with humid vapours, which 
caufed the thermometer of Fahrenheit, the 
bulb of which was placed in the holes 
from whence the vapours efcaped, to af- 
cend to 202}; and judging from the rapid 
elevation of the mercury, I believe the rife 
would have been confiderably mre in a 
thermometer whofe feale was more ex- 
tenfive: but miné being calculated for 
experiments upon the heat of animals, 
did got permit us this proof, terminating 
a few degrees beyond that of boiling 
water, Or 212. 
We did not find there either fulphur 
or hepatic air, but we perceived the imell 
of fomething burning, which I have al- 
ways found te accompany fuch orifices, 
and that rather refembles the odour of 
burning fulphur, but weak and. much 
attenuated. The rock whence proceeded 
thefe vapours, is a greenifh tufa, rich in 
magnefian earth, and im little pumice 
ftones, the whole corroded by moifture, 
and of confequence extremely tender. 
Around the orifice, but always at a {mall 
diftance, and upon the fides of the little 
cavern, we met with various incruftations 
refembling efflorefcences, produced there 
by the vapours: it will be fufficient te 
notice 
1. Chalk of a foliated form, abundant. 
2. Alum, but feldom, and in {mall 
quantities. 
3. Siliceous ftalactites, foliated, cylin- 
drical, or conical and pendent (mamillonate), 
very brittle, and of littie confiftence; on 
touching the tendereft points of it, which 
crumbled between the teeth, Iwas firft aware 
of their filiceous hardnefs. 
4. A bitter falt, of which I thall fpeak 
- hereafter. (Sec. 19.) . 
Afterwards, lower down the fteep and 
in the bottom of the channel itfelf, we 
found filiceous crufts, lefs delicate, but 
more compact than thofe before mention- 
ed, and fometimes coloured with red: 
there are alfo fome veins of the fame 
fubftance, which indicate the fite of other 
orifices already exhaufted. Penetrating 
afterwards a few inches within the mouth 
of the orifice now in activity, we found 
three groups of very white filiceous fta- 
lactites, of a mamillonate form, tender, 
and fo hot as not to permit us to retain 
them in our hands. (10.) Since then, by 
employing. much’ diligence, I have fuc- 
ceeded in finding: flphur mixed in the 
‘ aiae 6 “fubitanee 
> 
