Lightning Conductors: Their History, Nature, and Mode of Application

by F.C.S. Richard Anderson

Fig. 46. Fig. 47.

A variety of methods have been proposed for the dispersion of the electric force underground where the soil contains little or no moisture, except at great depths, to be reached only by a vast amount of labour and expenditure. In France, the system most generally adopted in these cases is to place at the bottom of the underground connection an apparatus, made either of iron or copper, shaped somewhat in the form of a harrow, and to embed it thickly in charcoal. [Fig. 48] will illustrate this system of earth connection.

Fig. 48.

The apparatus is as simple as it may be useful, and the more so, of course, the thicker the mass of charcoal in which it is embedded. But it may be doubted whether it is sufficient to make ‘good earth’ under all circumstances. Perhaps it will do so in ninety-nine cases and fail in the hundredth. The amount of electric force discharged in ordinary thunderstorms does not seem to vary much, and, according to all observations, such an artificial connection as this of the charcoal bed is sufficient to disperse it safely beneath the surface. But now and then there come storms of extraordinary violence, or, in other words, extraordinary accumulations of atmosphere electricity, which demand precautions such as are not fulfilled by the subterranean harrow, however thickly embedded in charcoal, or, as oftener done, in gas coke or cinders. It is certain that there have been cases in which buildings with otherwise excellent conductors, but provided with such an artificial earth connection, have been damaged by lightning. However, it may be stated, as the net result of all observations and known facts upon the subject, that small private houses can be well protected by this means against lightning, but that the system cannot be recommended as absolutely safe for large edifices and public buildings.

To protect any structure of great extent, it is absolutely necessary to bring the conductor, or conductors, deep enough into the earth to reach water. It is all the more indispensable with modern buildings, as they contain large masses of metal, not only in gas and water-pipes, but often in staircases and iron columns, towards which the electric force has the strongest tendency to direct itself unless drawn to the earth by an immediate and unfailing connection with the great sheet of water below its surface. It is considered by German electricians that there is no necessity, if a large edifice has a number of conductors, to let each have a separate earth connection; it is quite sufficient to bring them all into one, provided only that this is absolutely perfect at all seasons and under all circumstances. [Fig. 49] will show how this can be done.

Fig. 49.

It will be seen that for the protection of this edifice there are six conductors, with four elevated points marked A, B, C and c. Two of these points, A and C, expand from the roof to the ground into double conductors, so as to protect the sides of the building against possible lateral discharges of lightning, and all the six conductors meet a little below the surface in the earth connection prepared for them. To form this one connection, either by digging or boring, may sometimes be costly, but whether the expenses be more or less, the protection against lightning thus effected will be so absolute as to be invaluable.

In a similar manner as the large edifice, with its many gables, a church may be fitted with lightning conductors. [Fig. 50] scarcely needs much explanation.