PROTECTION FROM LIGHTNING.
Prof. Clerk Maxwell says that the ordinary lightning rod is a great mistake. It acts to discharge electricity from the clouds at all possible opportunities, but these discharges are smaller than would occur without the rod. The true method is to encase the building in a network of rods, when it will take its charge quietly like a Leyden jar. Taking the case of a powder mill, it would be sufficient to surround it with a conducting material, to sheathe its roof, walls, and ground-floor with thick sheet copper, and then no electrical effect could occur within it on account of any thunderstorm outside. There would be no need of any earth connection. We might even place a layer of asphalte between the copper floor and the ground, so as to insulate the building. If the mill were then struck with lightning, it would remain charged for some time, and a person standing on the ground outside and touching the wall might receive a shock, but no electrical effect would be perceived inside, even on the most delicate electrometer.
This sheathing with sheet copper is not necessary. It is quite sufficient to enclose the building with a network of a good conducting substance. For instance, if a copper wire, say No. 4, B. W. G. (0.238 inches diameter), were carried round the foundation of the house, up each of the corners and gables, and along the ridges, this would probably be a sufficient protection for an ordinary building against any thunderstorm in this climate. The copper wire may be built into the wall to prevent theft, but should be connected to any outside metal, such as lead or zinc on the roof, and to metal rain-water pipes. In the case of a powder-mill it might be advisable to make the network closer by carrying one or two additional wires over the roof and down the walls to the wires at the foundations. If there are water or gas pipes which enter the building from without, these must be connected with the system of conducting wires; but if there are no such metallic connections with distant points, it is not necessary to take any pains to facilitate the escape of the electricity into the earth. But it is not advisable to put up a tail pointed conductor.