Art. LXII.–A Flash of Lightning.

Transactions and Proceedings of the Royal Society of New Zealand, Volume 37, 1904, Page 580

Art. LXII.–A Flash of Lightning. By Archdeacon Walsh. [Read before the Auckland Institute, 12th September, 1904.] About last February a thunderstorm passed over the district of Taiamai, a tract of volcanic country lying about half-way between the Bay of Islands and Hokianga. The discharges were not very frequent, but were unusually heavy. One of them fell in a fairly level paddock close to the coach-road from Ohaeawai to Kaikohe, about half a mile from the former place. A wagon drawn by a team of horses was passing at the time, when the horses, terrified by the blinding flash, bolted, and the wagon was upset. It was raining in torrents, and a couple of Maoris, who were standing under the verandah of a cottage some three or four hundred yards off, stated that the

water appeared to bubble on the ground, and that steam kept rising for half an hour from the spot that had been struck. The phenomenon was plainly visible from the Township of Ohaeawai, and an animated discussion arose among some of the inhabitants as to its origin and results. By a too hasty generalisation the “thunderbolt”–as they agreed to call the electric discharge–was confused with the fall of a meteorite, and an individual who claimed to have some knowledge of the subject informed them that if the celestial visitor could be secured it would prove of considerable commercial value. He estimated that it would be worth at least .20, whether regarded merely as a curio or as a mass of marketable metal. Their scientific curiosity whetted by the hope of a financial return, a party of young men set out on a search expedition. They had no difficulty in finding the spot, and on arrival discovered a circular hole in the ground about 4 in. in diameter, surrounded by a number of similar perforations on a smaller scale, the whole set occupying a space of perhaps 2 or 3 yards square. It was evident that the discharge had split off into several branches on approaching the ground. It was not explained how twenty pounds' worth of meteoric iron could have forced its way through so narrow a passage; but, nevertheless, they started to dig. Failing, however, to bottom the hole at the depth of 6ft., they sounded with a piece of fencingwire, and as this went down for another 14 ft. the sinking was regretfully abandoned. Taking an early opportunity to visit the scene of operations, I found that the excavation had been filled up, and as the ground had been so trampled by the explorers all trace of the smaller holes had disappeared. I should like to have been able to examine the hole. There is no doubt that it was caused by the lateral expansion of the steam generated in the wet ground by the intense heat of the electric discharge. It is well known that on the passage of a lightning-spark through a bed of sand a tube of vitreous matter called a “fulgurite” is sometimes formed by the fusion of the particles of silica. Possibly some similar formation would take place in a stratum of clay; but in the volcanic ground of Taiamai, already subject to the extreme action of fire, it is unlikely that further metamorphosis could take place, and any change in the structure would be only due to compression. It would have been interesting, however, to see whether the compression had been sufficient to form a definite tube.