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Show 1832-3. MALDONADO. 70 d from the numb er of minute entanglhed scope, appeare ' b bbl like an assay fused before t e air or perhaps steam .u t~s, l or in greater part, siliceous ; blowpipe. ~he sand lsae~l:~y~olour, and from their glossy but some pomts are of . l rrhe thickness of the wall metallic ustre. · h surface posses~ a h' f th to a twentieth of an me ' of the tube vanes from a t llr Ie t th On the outside, the . ll equa s a en · and occaslOna y even d have a slightly glazed ap-grains of sand are roun~e~, a~ h y sign of crystallization. I ld not distmguis an . pearance: cou h t d 1. . ·bed in the Geological 1 er to t a escr In a sim. i ar tmh antnu bes are general ly compressed, and have TransactiOns, e losely to resemble a deep longitudinal furrows, soth as b:rk of the elm or cork shrivelled vegetable stalk, ?r b e t two inches but in some Th · circumference 1s a ou ' . ftrr ee. entse wirh i.C h are cy li n dn . cal and withou. t any furrho ws, It . agdm ble or four m. e h es. The compressiGn fro·m t e surd- IS o~ ' d ti while the tube was still softene ~~:;d;~: !::~ss:~ th:cin~;nse heat, has evidently causde~ th~ J d in from the uncom presse rag creases or furrows. u g g h r htnin (if such a term ments the measure or bore of t e 1g g t b' ed) must have been ab out one m· eh and a quar e.r . may e us ' d d m A P . M Hachette and M. Beaudant* succee e. t k' anst, bes · in most respects s.i m.i lar to the se fulguntes ' :ya PI:s~inug v:ry strong shocks of galvanism throug~ fi.nely-Powdered glass : when salt was a dd ed ' so as to . mcre.a se its fusibility, the tubes were l arger m· ev ery dimensiOOnne. They failed both with powdered felspar and quartz. . h tube, formed with pounded glass, was ve~ nearly an me l ong, namel y, ·9 89.... , and had an internal dmm. etepr o·f ·. 01a9s. When we hear that the strongest battery m ans w . . d and that the effect on a substance of such easy fusi-use ' . . . ust bility as glass, was to form tubes so dimmutlve, :Ve ~ feel greatly astonished at the power of a shock of lightmng, which striking the sand in several places, has formed a cylinder, in one instance of at least thirty feet long, and • Annales de Chimic et de Physique, tom. xxxvii., P· 319. 1832-3. F U LGURI'!'ES. 71 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 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-hiHocks; 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 subject 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 '!(.· Azara's Voyage, vol. i., p. 36. |