MALDONADO 



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 ^ 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, w^as 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 extraordinarih' 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 



^ Ainiahs dc Cliiniic et dr Physique, toni. xxxvii. p. 319. 



