greater depth. Four sets entered the sand perpendicularly: by working
with my hands I traced one of them two feet deep; and some fragments
which evidently had belonged to the same tube, when added to the other
part, measured five feet three inches. The diameter of the whole tube
was nearly equal, and therefore we must suppose that originally it
extended to a much greater depth. These dimensions are however small,
compared to those of the tubes from Drigg, one of which was traced to a
depth of not less than thirty feet.
The internal surface is completely vitrified, glossy, and smooth. A
small fragment examined under the microscope appeared, from the number
of minute entangled air or perhaps steam bubbles, like an assay fused
before the blowpipe. The sand is entirely, or in greater part,
siliceous; but some points are of a black colour, and from their glossy
surface possess a metallic lustre. The thickness of the wall of the
tube varies from a thirtieth to a twentieth of an inch, and
occasionally even equals a tenth. On the outside the grains of sand
are rounded, and have a slightly glazed appearance: I could not
distinguish any signs of crystallization. In a similar manner to that
described in the Geological Transactions, the tubes are generally
compressed, and have deep longitudinal furrows, so as closely to
resemble a shrivelled vegetable stalk, or the bark of the elm or cork
tree. Their circumference is about two inches, but in some fragments,
which are cylindrical and without any furrows, it is as much as four
inches. The compression from the surrounding loose sand, acting while
the tube was still softened from the effects of the intense heat, has
evidently caused the creases or furrows. Judging from the uncompressed
fragments, the measure or bore of the lightning (if such a term may be
used) must have been about one inch and a quarter. At Paris, M.
Hachette and M. Beudant [11] succeeded in making tubes, in most
respects similar to these fulgurites, by passing very strong shocks of
galvanism through finely-powdered glass: when salt was added, so as to
increase its fusibility, the tubes were larger in every dimension. They
failed both with powdered felspar and quartz. One tube, formed with
pounded glass, was very nearly an inch long, namely .982, and had an
internal diameter of .019 of an inch. When we hear that the strongest
battery in Paris was used, and that its power on a substance of such
easy fusibility as glass was to form tubes so diminutive, we must feel
greatly astonished at the force of a shock of lightning, which,
striking the sand in several places, has formed cylinders, in one
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