1832-3. 



FULGURITES. 



71 



having an internal bore^ where not compressed, of fuU 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 generality, had a deviation from a right 

 line, which amounted, at the most considerable bend, to 

 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 latter case is remarkable, as 

 the electric fluid must have turned back at the acute angle 

 of 26°, to the line of its main course. Besides the four tubes 

 which I found vertical, and traced beneath the surface, there 

 were several other groups of fragments, the original site of 

 which without doubt was near. All occurred in a level area, 

 sixty yards by twenty, of shifting sand, situated among some 

 high sand-hillocks : and at the distance of about half a mile, 

 from a chain of hills four or five hundred feet in height. 

 The most remarkable circumstance, as it appears to me, in 

 this case as well as in that of Drigg, and in one described by 

 M. Ribbentrop in Germany, is the number of tubes found 

 within such limited spaces. At Drigg, within an area of fifteen 

 yards, three were observed, and the same number occurred 

 in Germany. In the case which I have described, certainly 

 more than four existed within the space of the sixty by 

 twenty yards. As it does not appear probable that the 

 tubes are produced by successive and distinct shocks, we 

 must believe that the lightning, shortly before entering the 

 ground, divides itself into separate branches. 



The neighbourhood of the Rio Plata seems peculiarly sub- 

 ject to electric phenomena. In the year 1793,* one of the 

 most destructive thunderstorms perhaps on record happened 

 at Buenos Ayres : thirty-seven places within the city were 

 struck by lightning, and nineteen people killed. From facts 

 stated in several books of travels, I am inclined to suspect 



* Azaia's Voyage, vol. i., p. 36. 



