principal mineral constituent of the globe; the mass
of proof, also, is in favour of the guess that the
quartz shell holds in an internal fire. Miners,
well-borers, and well-sinkers whose operations
have gone far down into the crust of the Earth,
have given learned men opportunities of making
observations which prove that the heat of Earth
increases downward at the rate of about one
degree for every fifty feet. There is a point at
which the temperature is stationary, remaining
invariably at about two degrees above the mean
temperature of the climate. For half a century,
for instance, the temperature in the cellars of the
Paris Observatory, ninety feet down, has never
been above or below fifty-three degrees Fahrenheit.
This line under the surface would appear never
to be affected either by the solar or by the
terrestrial heat. But the heat of the strata of the
Earth, a concurrence of observations has proved,
increases at an average ratio of about one
degree in every fifty or sixty feet. The observations,
no doubt, differ among themselves; some
observers having found the increase to be one
degree in forty-five, and others one degree in
seventy-five feet, but the discrepancies are easily
accounted for by the differences in the qualities
of soils or strata. I have known some of the
men who have mounted highest up and some of
the men who have dug deepest down, and both
concur in saying they soon reached regions in
which breathing was attended with considerable
difficulties. Guy Lussac, who ascended in a
balloon four miles and a third, suffered much
from the difficulty of breathing in the highly
rarefied air; and, at a greater altitude, Mr.
Glaisher lost his senses for a short time. Marco
Polo and Alexander Humboldt, besides respiring
painfully upon lofty mountains, found it an
arduous task to kindle and maintain fires there.
There are similar difficulties deep down. Several
of the well-sinkers who dug the Warren Farm
Well, near Brighton, which is twelve hundred and
eighty-five feet deep, have told me their experiences.
It was unaccountably hot and sulphurous
down in the green sand. I have seen a marking
upon a thermometer, for the accuracy of
which I will not vouch, because it was so near
blood heat. But in a hole between three and
four feet in diameter, and twelve hundred
feet deep, strong men felt so weak that they
could not have lifted a glass of water to their
lips. When a workman once, in defiance of the
sternest prohibitions, took a bottle of ale with
him down to the bottom of the well, the heat
made the cork fly out, and the addition of the
carbonic acid gas in the liquid to the carbonic
acid gas from the respiration of the men at work
in the well, instantly put out all the lights—some
fifty or sixty lamps and candles, in the stages
above, extending nearly a quarter of a mile
upward.

Everything in the air comes from the Earth;
the very ashes and vapours of the central fires
rising up and mingling with the clouds. The
showers of volcanic ashes have occupied an
innumerable series of writers, from Pliny to the
correspondents of the newspapers, and I can
only take a passing glance at their grandeur
and terror. During the eruption of the volcano
Tomboro, in Sumbawa, in April, 1815, the
explosions were heard two hundred and seventeen
nautical miles distant. The war-ship Benares
was sent to ascertain the cause of the explosions,
and the commander reported what he saw. As
he approached nearer and nearer to the volcano,
the heavens assumed a dusky red appearance.
By ten o'clock in the morning, it became so dark,
that a ship could scarcely be discerned a mile
off. By eleven, the whole heavens were
obscured, except a small space whence the wind
came. At noon, this light disappeared, and
complete darkness covered the face of day. The
darkness surpassed the darkest night, during the
rest of the day, it being impossible to see a
hand held close to the eyes. Heaps of ashes, a
foot deep, were found in many places upon the
deck next day. But the volcanoes often send
forth far greater quantities of ashes. The ashes
and lapilli, which in the year 79 covered Stabio,
Pompeii, and Herculaneum, varied, it is
computed, in thickness from sixty to one hundred
and twelve feet. And these volcanic showers
may spread over vast regions. The eruption of
Shaptar-jökull, in 1783, filled the air of Iceland
with dust for a long time, and some of it was
traced even as far as Holland. The Souffrier of
Guadaloupe, in 1812, sent forth clouds of dust
which entombed the plants and animals of many
vast regions in the tropics; and, strange to tell,
some of these clouds of ashes were carried as
far as Barbadoes by an upper current of air
running in an opposite direction to the trade
winds.

The ashes of the volcanoes are different and
characteristic. I find among my notes an
account of an eruption, the ashes from which, at
one period of it, resembled red earth. This
eruption took place from a mountain called Jebel
Dubbeh, on the African shores of the Red Sea,
about half way between Massowah and the straits
of Bab-el-mandeb. Early in the morning of the
8th of May, 1861, the people of the village of
Edd were awakened by the shock of an earth-
quake, and for about an hour the shocks
continued without intermission. At sunrise, fine
white dust began to fall over the village, like
rain; at about noon the dust which fell, changed
its hue from white to red. It then resembled
red earth. Of this red dust so much fell that
the day became quite dark, and the villagers had
to light lamps in their houses. It was darker
than the darkest night, and the dust lay knee-
deep. On the following day, there was light
enough to see in the houses without lamps.
That night, fire and thick smoke were seen issuing
from a mountain situated about a day's
journey inland, and called Jebel Dubbeh. The
ashes fell for only two days; but the fire and
smoke issued for some weeks from the mountain.
Nothing of the kind had ever happened before,
and the people of the village of Edd were
exceedingly frightened.

Not merely have we authentic if not scientific
accounts of showers of red ashes from