Lightning, Thunder and Lightning Conductors

by Gerald Molloy

Cases are not uncommon in which builders provide underground a carefully constructed reservoir of water, into which the lower end of the lightning rod is introduced. The idea seems to prevail that a reservoir of water constitutes a good earth contact; and this is quite true of a natural reservoir, such as a lake, where the water is in contact with moist earth over a considerable area. But an artificial reservoir may have quite an opposite character, and practically insulate the lightning conductor from the earth. One which came under my notice lately, in the neighborhood of this city, consists of a large earthenware pipe set on end in a bed of cement, and kept half full of water. Now, the earthenware pipe is a good insulator, and so is the bed of cement in which it rests; and the whole arrangement is identical, in all essential features, with the apparatus of Professor Richman, in which he introduced his lightning rod into a glass bottle, and by which he lost his life a hundred and thirty years ago.

A conductor mounted in this manner will, probably enough, draw down lightning from the clouds; but it is more likely to discharge it, with destructive effect, into the building it is intended to guard, than to transmit it harmlessly to the earth. An example is at hand in the case of Christ Church, in the town of Clevedon, in Somersetshire. This church was provided with a very efficient system of lightning conductors, five in number, corresponding to the four pinnacles and the flagstaff, on the summit of the principal tower. The five conductors consisted of good copper-wire rope; all were united together inside the tower, through which they were carried down to earth, and there ended in an earthenware drain. This kind of earth contact might be pretty good as long as water was flowing in the drain; but whenever the drain was dry the conductor was practically insulated from the earth. On the fifteenth of March, 1876, the church was struck by lightning, which for some distance followed the line of the conductor; then finding its passage barred by the earthenware drain, which was dry at the time, it burst through the walls of the church, displacing several hundredweight of stone, and making its way to earth through the gas-pipe.[34]

Another very instructive example is furnished by the lightning conductor attached to the lighthouse of Berehaven, on the south-west coast of Ireland. It consists of a half-inch copper-wire rope, which is carried down the face of the tower “until it reaches the rock at its base, where it terminates in a small hole, three inches by three inches, jumped out of the rock, about six inches under the surface.” Here, again, we have a good imitation of Professor Richman’s experiment, with only this difference, that a small hole in the rock is substituted for a glass bottle. A lightning conductor of this kind fulfills two functions: it increases the chance of the lightning coming down on the building, and it makes it positively certain that, having come, it cannot get to earth without doing mischief.

The lightning did come down on the Berehaven Lighthouse, about five years ago. As might have been expected, it made no use of the lightning conductor in finding a path to earth, but forced its way through the building, dealing destruction around as it descended from stage to stage. The Board of Irish Lights furnished a detailed report of this accident to the Lightning Rod Conference, in March, 1880, from which the above particulars have been derived.[35]

Precaution Against Rival Conductors.—But it is not enough to provide a good lightning conductor, which is itself able to convey the electric discharge harmless to the earth; we must take care that there are no rival conductors near at hand in the building, to draw off the lightning from the path prepared for it, and conduct it by another route in which its course might be marked with destruction. This precaution is of especial importance at the present day, owing to the great extent to which metal, of various kinds, is employed in the construction and fittings of modern buildings. I will take a typical case which will bring home this point clearly to your minds.

A great part of the roof of many large buildings is covered with lead. The lead, at one or more points may come near the gutters intended to collect the rain water; the gutters are in connection with the cast-iron down-pipes into which the water flows, and these down-pipes often pass into the earth, which, under the circumstances, is generally moist, and, therefore, in good electrical contact with the metal pipes. Here, then, is an irregular line of conductors, which, though it has gaps here and there, may, under certain conditions, offer to the lightning discharge a path not less free than the lightning conductor itself. What is the consequence? The flash of lightning, or a part of it, will quit the lightning rod, and make its way to earth through the broken series of conductors, doing, perhaps, serious mischief, as it leaps across, or bursts asunder, the non-conducting links in the chain.

Another illustration may be taken from the gas and water-pipes, with which almost all buildings in great cities are now provided, and which constitute a network of conductors, spreading out over the walls and ceilings, and stretching down into the earth, with which they have the best possible electrical contact. Now, it often happens that a lightning conductor, at some point in its course, comes within a short distance of this network of pipes. In such a case, a portion of the electrical discharge is apt to leave the lightning conductor, force its way destructively through masses of masonry, enter the network of pipes, melt the leaden gas-pipe, ignite the gas, and set the building on fire.

These are not merely the speculations of philosophers. All the various incidents I have just described have occurred, over and over again, during the last few years. You will remember, in some of the examples I have already set before you, when the electric discharge failed to find a sufficient path to earth through the lightning rod, it followed some such broken series of chance conductors as we are now considering. But this broken series of conductors seems to bring with it a special danger of its own, even when the lightning conductor is otherwise in efficient working order. I will give you just one case in point.

On the fifth of June, 1879, the Church of Saint Marie, Rugby, was struck by lightning and set on fire, and narrowly escaped being burned to the ground. A number of workmen were engaged on that day in repairing the spire of the church. About three o’clock they saw a dense black cloud approaching, and they came down to take shelter within the building. In a few minutes they heard a terrific crash just overhead; at the same moment the gas was lighted under the organ loft and the woodwork was set in a blaze. The men soon succeeded in putting out the fire, and the church escaped with very little damage.

Now, in this case there was no reason to suppose that the lightning conductor was in any way defective. But about half-way up the spire there was a peal of eight bells. Attached to these bells were iron wires, about the eighth of an inch in diameter, leading from the clappers down to the organ-loft, where they came within a short distance of a gas-pipe fixed in the wall. It would seem that a great part of the discharge was carried safely to earth by the lightning conductor. But a part branched off at the bells in the spire, descended by the iron wires, and forced its way into the organ loft, to reach the network of gas-pipes, through which it passed down to the earth, melting the soft leaden gas-pipe in its course and lighting the gas.