CO MALDONADO. [chap. iii. 



tubes projected above the surface ; and numerous fragments 

 lying near, 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 

 deptli. These dimensions are however small, compared to those 

 of tiie 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 : 1 could not distinguish any 

 signs of crystallization. In a similar manner to that described 

 in the Geological Transactions, the tubes are generally com- 

 pressed, 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 surround- 

 ing 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 mea- 

 sure or bore of tiie 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 



♦ Aimales de Chimie et do Physique, tora. xxxvii., p. 319. 



