143 
the electric fluid/* when an explosion takes place, and if the vent be sufficient 
from the open crater of the agitated volcano, an earthquake is avoided, 
observed in another place, that they formerly obtained a sort of tar from a stone at Broseley; and the 
stratum which is called shale in Derbyshire, is so strongly impregnated with oil, that it will burn of 
itself, when set on fire: the workmen in digging through the black stone, which is incumbent on 
the shale, sometimes meet with cavities containing a thick black oil, which has oozed out of the sur¬ 
rounding stone. One of the greatest soughs, or subterraneous passages, which has, perhaps, ever been 
formed in great Britain, is that which is called Hell-car sough, in Derbyshire; this sough is driven 
through a stratum of shale, and the workmen are much troubled with inflammable air, which gene¬ 
rally breaks into the sough, through the same crannies which give passage to little streams of water; 
they secure themselves from the air, by keeping great fans constantly in motion; for the inflammable 
air, being lighter than common air, floats near the roof of the sough, and being drawn down from 
thence, and mixed with the common air by the motion of the fans, it is circulated in the sough with¬ 
out danger. I am sensible that inflammable air may be produced by various other ways, as well as 
by the application of heat, to bituminous strata; but as bitumens do yield this air by distillation, it 
is probable enough, that such as is met with in bituminous strata, may sometimes, at least, be referred 
to the action of fire, situated, perhaps, at too great a distance from the surface of the earth to produce 
any other sensible effect. Vide the Bishop of LlandafFs very amusing and instructive Chemical Essays. 
In the Duchy of Modena in Italy, there is a remarkable rock, which confirms very much the notion 
of oils and pitchy substances being separated from bitumens by a kind of subterraneous distillation. 
The-inhabitants of the district, by piercing the sides of this rock, at different distances from its summit, 
obtain oil of different natures, thickening and growing heavier and deeper coloured, as the canals 
through which they flow approach to the surface of the earth; at the distance of a few feet below the 
surface of the earth, they find a very thick oil, which in digging deeper becomes soft as butter, and at 
still a greater depth, it is found to be as solid as pitch. 
Near Derbens, on the Caspian Sea, there are springs of naptha, which Kempfer visited about a cen¬ 
tury ago, and of which he has left a description. 
There is a place known by the nkme of the Perpetual Fire, where the fire burns without ceasing. 
The Indians do not attribute the origin of this inextinguishable fire to naptha; but they maintain that 
God has confined the Devil in this place, to deliver man from him. They go in pilgrimage thither, and 
make their prayers to God that he will not suffer this enemy of mankind to escape. 
The earth impregnated wuth naptha is calcareous, and effervesces with acids; it takes fire by the 
contact of any ignited body whatever. 
This perpetual fire is of great use to the inhabitants of Baku. They pare off the surface of this 
burning soil, upon which they make a heap of limestones, and cover it with the earth pared off; and 
in two or three days the lime is made. 
The inhabitants of the village of Frogann repair to this place to cook their provisions. 
The Indians assemble from all parts to adore the Eternal Being in this place. Several temples were 
built, one of which is still in existence. Near the altar there is a tube inserted in the earth, two or 
three feet in length; out of which issues a blue flame, mixed with red. The Indians prostrate them¬ 
selves before this tube, and put themselves into attitudes which are exceedingly strange and painful. 
Concerning the accension of different bodies by the mineral acids, vide note * page (102). 
* The observations made by Sir William Hamilton on the last tremendous eruption of mount Vesu- ' 
vius, shew how much the electric fluid is concerned in volcanic explosions. 
“ The black smoke of ashes, says this author, issuing continually from so many new mouths or craters, 
formed an enormous dense body of clouds over the whole mountain, and which began to give signs of 
being replete with the electric fluid, by exhibiting flashes of that sort of zig-zag lightning, which, in 
the volcanic language of this country, is called ferilli, and which is the constant attendant on volcanic 
eruptions. 
During thirty years that I have resided at Naples, and in which space of time I have been witness- 
to many eruptions of Vesuvius, of one sort or other, I never saw the gigantic clouds above-mentioned 
