72 CHARLES DARWIN 



regular than the others, deviated from a right line, at the 

 most considerable bend, to the amount of thirty-three de- 

 grees. 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 elec- 

 tric 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 sites of which 

 without doubt were near. All occurred in a level area of 

 shifting sand, sixty yards by twenty, 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 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 I793, 12 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 

 that thunderstorms are very common near the mouths of 

 great rivers. Is it not possible that the mixture of large 

 bodies of fresh and salt water may disturb the electrical 

 equilibrium? Even during our occasional visits to this part 

 of South America, we heard of a ship, two churches, and a 

 house having been struck. Both the church and the house 

 I saw shortly afterwards: the house belonged to Mr. Hood, 

 the consul-general at Monte Video. Some of the effects were 

 curious : the paper, for nearly a foot on each side of the line 



"Azara's Voyage, voL i. p. 36- 



