Among the regions peculiarly subject to electric phenomena is the country around the estuary of the Rio Plata. In the year 1793, one of the most destructive thunder-storms perhaps on record, happened at Buenos Ayres, when thirty-seven places in the city were struck by the lightning, and nineteen of the inhabitants killed. It is an observation of Mr. Darwin, founded on statements in books of travels, that thunder-storms are very common near the mouths of great rivers; and he conjectures that this may arise from the mixture of large bodies of fresh and salt water disturbing the electrical equilibrium. “Even,” he remarks, “during our occasional visit 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 afterward. Some of the effects were curious: the paper, for nearly a foot on each side of the line where the bell-wires had run, was blackened. The metal had been fused, and although the room was about fifteen feet high, the globules, dropping on the chairs and furniture, had drilled in them a chain of minute holes. A part of the wall was shattered as if by gunpowder, and the fragments had been blown off with force sufficient to indent the wall on the opposite side of the room. The frame of a looking-glass was blackened; the gilding must have been volatilized, for a smelling-bottle, which stood on the chimney-piece, was coated with bright metallic particles, which adhered as firmly as if they had been enameled.” Near the shores of the Rio Plata, in a broad band of sand hillocks, he found those singular specimens of electric architecture, a group of vitrified siliceous tubes, formed by the lightning striking into loose sand. These tubes had a glossy surface, and were about two inches in circumference, the thickness of the wall of each tube varying from the twentieth to the thirtieth part of an inch. Four sets were noticed, probably not produced by successive distinct charges, but by the lightning dividing itself into separate branches before entering the ground. Similar cylindrical formations have been noticed in other places. Dr. Priestley has described, in the Philosophical Transactions, some siliceous tubes, which were found in digging into the ground, under a tree, where a man had been killed by lightning; and at Drigg, in Cumberland, three were observed within an area of fifteen yards, one of which was traced to a depth of not less than thirty feet. In the temperate climates electrical phenomena are most common, and usually most energetic in the summer season, and the displays are grander and more formidable in mountainous than in level countries. As we approach the poles, they become less striking; thunder is rarely heard in high northern latitudes, and only as a feeble detonation; and though lightning is more common, it is seldom destructive. In Iceland, in the winter, it often plays in the impressive but harmless manner which the natives call laptelltur.