62 
MALDONADO 
CHAP. 
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 sur¬ 
rounding 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 1 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 light¬ 
ning, which, striking the sand in several places, has formed 
cylinders, in one instance of at least thirty feet long, and having 
an internal bore, where not compressed, of full an inch and a 
half; and this in a material so extraordinarily refractory as 
quartz ! 
The tubes, as I have already remarked, enter the sand nearly 
in a vertical direction. One, however, which was less regular 
than the others, deviated from a right line, at the most consi¬ 
derable bend, to the amount of thirty-three degrees. From this 
same tube, two small branches, about a foot apart, were sent 
off; one pointed downwards, and the other upwards. This 
1 Annates de Chirnie et de Physique , tom. xxxvii. p. 319. 
