70 JIALDONADO. 1832-3. 



scope, 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 ap- 

 pearance : I could not distinguish any sign of crystaUization. 

 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 double, or four inches. The compression from the sur- 

 rounding loose sand, acting while the tube was stiU softened 

 from the effects of the intense heat, has evidently caused the 

 creases or furrows. Judging from the uncompressed frag- 

 ments, 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. Beaudant* 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. 

 When we hear that the strongest batterv in Paris was 

 used, and that the effect on a substance of such easy fusi- 

 bility as glass, was to form tubes so diminutive, we must 

 feel greatly astonished at the power of a shock of hghtning, 

 which, striking the sand in several places, has formed a 

 cylinder, in one instance of at least thirty feet long, and 



* Annales de Chimie et de Physique, torn, xxxvii., p. 319. 



