Fig. 50.
There is one thing, however, regarding churches, that must be well borne in mind in establishing their protection against lightning. Besides containing great masses of metal, in bells, organs, and other contents, they are frequently placed in high situations, exposed to the most violent discharges of the electric force. It often happens also that they stand on rocky ground, with the subterranean waters far below the surface. To ensure absolute protection under these circumstances, it is indispensable to connect the conductors with water, wherever it is to be found, by a solid channel, into which the copper rods may run, if possibly some distance below the surface of the earth. The form such a channel may take is indicated on the engraving. It will be seen that the protection against lightning indicated here is not only for the church, but the adjoining parsonage, the conductors spreading over both, with points on the most prominent and exposed places. It would be possible to carry out this principle in ensuring the protection of a whole block of private buildings. German electricians think that one channel or well, sufficiently broad, leading from the surface of the earth to layers always moist, or to perennial springs, would suffice to carry the electric force discharged upon a hundred conductors, and all the easier as it would be impossible that many would be struck at one and the same time by lightning. Perhaps some such arrangements will be made in the future, when both houses and towns are built upon a more systematic plan than is followed at the present time.
If, as a rule, one channel of underground connection is amply sufficient for the protection of even the largest buildings, there may be cases in which it is indispensable to spread the conductors into several directions. It may be laid down, broadly, that when there is water to be reached, the one channel is sufficient, but that when this is not possible, or expedient, more lines of underground connection must be formed. [Fig. 51] may serve to illustrate a case of the latter kind. It shows a powder-magazine, partly above and partly underground, standing on dry soil, with trees in the neighbourhood, likely to add to the danger of atmospheric discharges of electricity, and with no stream, or permanent moisture, into which to guide them. Nothing remains, under these circumstances, to ensure safety, but to multiply the lines of underground connection to the utmost extent. To add to the facility of the dispersion of the electric force, the main channels may be filled with charcoal, broken coke, or cinders, and if large quantities of these substances can be placed in one or two pits, it is possible to make thus an artificial connection as nearly as can be responding to ‘good earth.’ Still, it must never be forgotten that, absolutely, ‘good earth’ in reference to lightning conductors means moisture, or water.
If permanent moisture cannot be obtained and iron water-mains are within reach, it is desirable to connect the ground terminal with them by means of good solder, as from the large mass of metal they generally form very good ‘earths.’
Fig. 51.
In giving directions, or rather suggestions, about the design and application of conductors, and, what is most important in regard to them, their connection with the subterranean mass of waters, the idea that persons may construct their own conductors is left aside altogether as absurd. It is a good old proverb which says that a man who is his own lawyer is certain to lose his cause; another has it that a man who is his own doctor is sure to succumb to his illness. With regard to the setting-up of lightning conductors, it is precisely the same. Simple enough as is the theory of ‘drawing lightning’ from the clouds, the practical execution of it is, as mentioned more than once, not a little complicated. The formation of the underground connection, in particular, is a matter requiring very great experience, and very frequently one of the utmost difficulty. Vast sums of money are often thrown away needlessly in making a connection which in the end proves useless, while, on the other hand, a trifling addition to the expenditure in setting-up a conductor would procure its efficiency, not attained simply from want of ‘good earth.’ A recent writer on lightning conductors whimsically, yet with much truth, expresses it by remarking that ‘people spend money upon gilded points on the top of the house, while they ought rather to sink it in water at the bottom.’ Undoubtedly, the efficiency of conductors lies, even more than at the top, on ‘the bottom.’ The earth connection may be called ‘the alpha and omega’ of lightning protection.