‘But the most singular fact, in a certain respect, is what was observed in the tube which descends to Alatri--that is to say, the alteration in form of the leaden slab. The little interruption which necessarily exists in this tank between the conducting-pipe and the metallic receptacle evidently gave occasion for a discharge by a flash, and, in consequence, for an explosion of steam. But we see at the same time by that that the distance traversed in the tube from the building to the slab, a distance of more than 200 metres [650 feet], in which the pipe is buried underground, did not suffice for the charge to lose itself in the ground, although during the passage it had to cross the reservoir, and might there have distributed itself. Our surprise is still greater when we reflect that it was only part of the discharge, since the greater portion had to flow by the water-pipe of Ferentino, which was the first struck in a direct manner, and that these pipes are joined together with lead. The quantity of electricity must have been enormous, in order to be able to have so much force and to run another 300 metres [975 feet] to reach the public fountain, and leave its traces there. A circumstance which deserves attention is, that this storm took place after a long and constant drought; and consequently the earth was less moist, and could offer little facility for dispersion.
‘These cases are not so rare among us as one might suppose. Not very long ago, at Lavinia, a flash of lightning destroyed a great part of the belfry, passed to the bell, broke and melted it in its passage in such a manner that the metal had run away like wax. I do not believe this breakage of the bell to have been a mechanical effect of the lightning in a rigorous sense, for the bell could have been broken by the instantaneous expansion produced by the heat at the point of the passage, an expansion which had had no time to disperse, as a glass vase breaks when touched with a red-hot iron.
‘Let these facts come about how they may, they enable us to see that it is necessary to devote great attention in the erection of lightning conductors, that we must allow them a large surface for discharge, _and that there can never be too much of it_. The surface of the foot of our lightning conductor was certainly superior to what has been judged sufficient by Matteucci for the discharges of telegraphic conductors, and yet it has not sufficed. Further, it is a confirmation of the necessity of making the neighbouring metallic masses communicate, and especially with water and gas-pipes.’
