showed that they had formerly been buried to a 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 crystallisation. 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 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.
(3/11. "Annales de Chimie et de Physique" tome 37 page 319.) They
failed both with powdered feldspar 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 tha