With Regard To The Internal Machinery By Which These
Waterworks Are Set In Motion, I Will Only Say That The
Most received theory seems to be that which supposes the
existence of a chamber in the heated earth, almost, but
Not quite, filled with water, and communicating with the
upper air by means of a pipe, whose lower orifice, instead
of being in the roof, is at the side of the cavern, and
BELOW the surface of the subterranean pond. The water
kept by the surrounding furnaces at boiling point,
generates of course a continuous supply of steam, for
which some vent must be obtained; as it cannot escape by
the funnel, the lower mouth of which is under water, it
squeezes itself up within the arching roof, until at
last, compressed beyond all endurance, it strains against
the rock, and pushing down the intervening waters with
its broad, strong back, forces them below the level of
the funnel, and dispersing part, and driving part before
it, rushes forth in triumph to the upper air. The fountains,
therefore, that we see mounting to the sky during an
eruption, are nothing but the superincumbent mass of
waters in the pipe driven up in confusion before the
steam at the moment it obtains its liberation. [Footnote:
Professor Bunsen has lately announced a chemical theory,
which I believe has been received with favour by the
scientific world. He points to the fact that water, after
being long subjected to heat, loses much of the air
contained in it, has the cohesion of its molecules much
increased, and requires a higher temperature to bring it
to boil; at which moment the production of vapour becomes
so great, and so instantaneous, as to cause explosion.
The bursting of furnace boilers is often attributable to
this cause. Now, the water at the bottom of the well of
the Great Geysir is found to be of constantly increasing
temperature up to the moment of an eruption, when on one
occasion it was as high as 261 degrees. Fahrenheit.
Professor Bunsen's idea is, that on reaching some unknown
point above that temperature, ebullition takes place,
vapour is suddenly generated in enormous quantity, and
an eruption of the superior column of water is the
consequence.]
The accompanying sketch may perhaps help you to understand
my meaning.
[Figure: fig-p074.gif]
The last gulp of water had disappeared down the funnel.
We were standing at the bottom of the now empty basin,
gazing into each other's faces with joyous astonishment,
when suddenly we perceived a horseman come frantically
galloping round the base of the neighbouring hill towards
us. The state of the case was only too evident. He had
seen the masses of vapour rising round the fountain, and
guessing "what was UP", had strained every nerve to arrive
in time. As there was no mutual friend present to
introduce us to each other, - of course under ordinary
circumstances I should have wrapped myself in that reserve
which is the birthright of every Briton, and pretended
never even to have noticed his arrival; but the sight we
had just seen had quite upset my nerves, - and I confess,
with shame, that I so far compromised myself, as to
inaugurate a conversation with the stranger.
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