1832-3.] ELECTRIC PHENOMENA. 61 



dimension. They failed both with powdered felspar and quartz. 

 One tube, formed with poimded 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 fusi- 

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

 greatly astonished at the force of a shock of lightning, 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 con- 

 siderable bend, to the amoinit 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 

 latter case is remarkable, as tlie 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 be- 

 neath the surflice, there were severjil otlier groups of frag- 

 ments, the original sites of which without doubt were near. 

 All occurred in a level area of shifting sand, sixty yards by 

 twenty, situated among some higli sand-hillocks, and at the dis- 

 tance of about half a mile from a cliain 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. Kibbentrop in Germany, is tlie 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 distinct shocks, we must believe that the 

 lightning, sliortly before entering the ground, divides itself into 

 separate branches. 



The neighbourhood of the Eio Plata seems peculiarly subject 

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



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



