FOG. 531 
fend annually numerous flocks. There were every where 
florins of rain ; and after thefe ftorms the fog fometimes 
increafed, but mod frequently was diminifhed. During 
the whole time of the fog, an eleiSlric machine I had at 
Sallon emitted few or no fparks. A philofophic friend 
at Sorgues, near Avignon, wrote to me, that his eleftro- 
meter always indicated a great deal of electricity in the 
atmofphere. 
“ On the 4th of July, at five in the morning, M. Nico¬ 
las, phvfician at Grenoble, and M. Plana, apothecary, 
took four meafures of fog and mixed them with twomea- 
fures of nitrous air: the abforption was one-fourth, and 
nothing remained but a gas, in which a candle became ex¬ 
tinguished feveral times. Atmofpheric air generally con¬ 
tains nearly one-third of pure air (oxygen gas), and two- 
thirds of mephitic air (azotic gas). Fontana’s eudiome¬ 
ter gave the fame refult on the 7th of July : of three hun¬ 
dred parts of atmofpheric air, thirty-two were abforbed. 
The air of the fog, mixed with inflammable (hydrogen) 
gas, did not prevent it from exploding when a lighted ta¬ 
per was prefented to the neck of the bottle in which it 
was contained, 
“ Almoft all thofe who have fpoken of this fog fay that 
it was low. When I was on the top of Mount Ventoux, 
however, nearly 1040 toifes above the level of the fea, I 
faw it far above me. M. Senebier fays, in his letter to 
count de Saluces, that it was feen in the Alps at an ele¬ 
vation greater than that of Mount Saleve, which rifes 601 
toifes above the fea. On the 226 of September 1783, I 
afcended the higheft Alps of Dauphiny, to the height of 
1660 toifes above the fea. The (hepherds, who ferved 
me as guides, all allured me that this fog had palled over 
thefe mountains. The lowed part of the fog was the 
tliickeft and dried. I allured myfelf of this by proceed¬ 
ing from the borders of the fea to the fummits of the 
highed mountains. 
“ It is probable, according to every account, that this 
fog overfpread almod all Europe, the iflands of the Me¬ 
diterranean, and a part of Africa. It covered the w'hole 
Adriatic Sea, but extended only to the didance of one 
hundred leagues on the ocean. It was properly a conti¬ 
nental fog. The thunder which attended it occafioned 
great devadation. In Provence and Dauphiny alone it 
killed nearly fixty perfons, and a great number of animals. 
1 have found no indance of its falling and doing mifchief 
in places higher than 450 toiles above the level of the fea. 
“ Several philofophers adopted the opinion of the po¬ 
pulace, and conlidered this fog as a natural effetd of the 
earthquake which laid wade Sicily and a part of Calabria. 
Toaldo thought that all thefe exhalations were brought 
from Calabria and Sicily by tire winds which "blew from 
the fouthward : but this refpedlable philofopher, at the 
time when he wrote, did not know that the fog was almod 
general throughout Europe. Befides, the earthquakes in 
Calabria and Sicily took place chiefly in February, and 
the fog did not appear till the middle of June ; that is to 
fay, till more than four months after. In my opinion, 
then, this fog was not occafioned by the. earthquakes of 
Calabria and Sicily ; but the fog and thefe earthquakes, 
as well as thofe which we are allured took place in Ice¬ 
land, had a common caufe, which produced different ef¬ 
fects according as they were modified by circumflances 
and the nature of the places. Let us now fearch for this 
caufe; we (hall find it in the annals of meteorology, and 
nothing is necedary but to didinguifl) it. 
“ I have given it as my opinion, that the conflitution 
cf the atmofphere depends chiefly on the nature and form 
of the ground, and that the revolutions of the air are fub- 
jebl to the revolutions of the earth, over which they have 
an influence in their turn. If we confider the different 
bodies or fubftancesof which that part of theearth knowjr 
to us is compofed, we {hall fee that, notwithftanding their 
apparent reft, they all obey an inteftinal motion ; and that 
this motion gives continual rife to new compolitions and 
combinations, the connexion of which efcapes us,, but 
which neverthelefs exiff. The remains of animals and 
vegetables ftill diftinguifhabie, and which occupy formtch 
room in our globe; the acids which attack them ; the 
aeriform fluids difengaged from them ; the metals and 
pyrites brought to perfection, or decoinpofed ; the fires 
Separated, or collected ; the fermentations and efferve- 
fcences; in a word, the innumerable decompofitions and 
recompofitions of all the parts, of the earth, furnifh abun¬ 
dance of fubtle matter, which, by its levity, difengagesitfelf 
at the furface of the globe, cannot, in certain circum- 
ftances, refill the gravity of the air, and rifes fometimes to 
the fummit of the atmofphere. On the other hand, the 
rains which fall, moift: fogs, and feveral other caufes, 
make a part of the water, which detaches itfelf from the 
air, to penetrate the earth, and to combine with the fub- 
ftance of thefe exhalations. It is afterwards, in part, at¬ 
tracted by the external heat, or repelled by the heat of 
the earth itfelf; but it never returns to the atmofphere 
as pure as it was when it iffiied from it. It carries with 
it a great part of that fubtle matter of which I have fpo¬ 
ken ; and it is this afterwards which produces lightning, 
and almoft all fiery meteors. There is then a continual 
communication from the earth to the atmofphere, and 
from the atmofphere to the earth. The greater part of 
thefe exhalations, in general, is fpecifically heavier than 
the atmofpheric air ; and, if they are not impregnated with 
acertain quantity of water, they cannot quit the earth. 
They muff neceflarily be there collected, and accumulate 
to a greater or lefs depth in the time of great droughts. 
“ Let us now confult our regifters, and thofe of differ¬ 
ent obfervers, and we {hall fee that there had prevailed, 
at lead for nine years, an extreme drought, not only in 
Europe, but alfo in Africa and America. This was an¬ 
nounced year after year by our domeftic as well as foreign 
gazettes; and we may conclude fo from the minute ob- 
fervations of the celebrated Van Swinden, and the tables 
publifhed by Toaldo, Cotte, Beraud, Beguelin de Ro- 
mily, &c. Sometimes, indeed, rain took place in one 
country or other ; but in general, till the preceding win¬ 
ter, an extraordinary drought prevailed. It began about 
1774, and in the month of June 1782 was extremely great 
in Italy and in our fouthern provinces. We experienced 
at that period a fuffocating heat ; the earth, as we may 
fay, feemed to be on fire, and, in the Plain ot Camargue, 
fcorched the feet of the reapers to fuch a degree that they 
were obliged at length to walk upon ftraw : {everal died 
of heat with the fickles in their hands, and there were a 
great many fick. In a word, the drought and heat were 
fo exceffive, that, at two leagues from Salion, the fpiders, 
which in general are not venomous, occafioned by their 
bite violent difeafes, which had a great affinity to thofe 
occafioned by the bite of the tarantula. 
“ In confequence of this great drought, the exhalations 
of the earth, fpecifically heavier than the air, and deprived 
of that humidity which ferves them as a vehicle, remain¬ 
ed in the bofom of the earth, where they muff have iortped 
immenfe accumulations. The winter of 1782-1783 was 
rainy, particularly in Calabria and Sicily ; and .the Alps 
were covered with a great deal of fnow. The fpring al¬ 
fo was in general rainy. The w'ater, then, being El tered 
into the bowels of the earth, was at firft abforbed h' : the 
very dry exhalations there confined. This humidity, 
added to the warmth of the fpring, no doubt occafioned 
effervefcences and fermentations ; fo t hat the exhalations, 
difengaging themfelves with violence, in certain places 
convulfed the earth, as was the cafe in Calabria and Si¬ 
cily. In proportion as the water filtered into the earth 
by its own weight, it found new exhalations, which, by 
difengaging themfelves, occafioned new convulfions, but 
lefs confiderable on account of the lefs abundance of thefe 
exhalations. In places where they were heated by their 
mixture, they liquefied ftones, and threw up volcanic 
iflands, as in Iceland. In the la It place, thefe lubtle ex¬ 
halations riling into the atmoiphere from all parts, with 
the vapours which ferved them as a vehicle, did not at 
firft 
