CHAPTER XVI
INSPECTION OF LIGHTNING CONDUCTORS.
There is one subject in regard to the proper protection of buildings against the destructive effects of lightning which is generally overlooked, at least in this country, to a really surprising degree. It is the necessity that lightning conductors, once put up, should be regularly inspected, to see if they are in good order, so as to be really efficacious. That this is very rarely done, is one of the main reasons why accidents by lightning sometimes occur in places nominally protected by conductors. The neglect is the more astounding, as one would think that all intelligent persons, whose knowledge prompted them to see the wisdom of protection against lightning, would likewise come to the conclusion that the scientific apparatus set up to effect it required occasional repairs, such as the clocks in their houses and the buildings themselves. But such is very far from being the case. It is, perhaps, not too much to assert that at present not one in a thousand persons who have gone to the expense of protecting their houses by lightning conductors make the protection complete, at a merely nominal cost, by providing a regular—say, annual or bi-annual—inspection.
The causes which necessitate such inspection are numerous. In the first instance, there is the constantly acting influence of wind and weather upon those parts of the conductor which are above earth. Wonderful as is the simple machinery devised by Franklin which conducts the mysterious electric force from the clouds into the ground, depriving it of its destructive power, it is, after all, but a feeble thing in itself, and necessarily so. The upper terminal of the conductor—what the Germans call the ‘reception rod,’ and the French the ‘tige,’ or stem—cannot be very thick without becoming unsightly, and, as regards large public buildings, destroying their architectural effects; while the rope, or ribbon, running to the ground must, for the same reason, as well as that of cost, be of comparatively small diameter. Subject to the constant effects of moisture, to wind, and ice, and hailstorm, there is always a possibility of the slender metal strips being damaged, so as to interrupt their continuity, and thus destroy the free passage of the electric force. Instances have happened in which the damage done was so slight as to be scarcely visible, and still sufficient to destroy the efficacy of the conductor. Nothing but the regular testing by a galvanometer—one of which is described, with an illustration, on page 60—by an experienced person can establish the fact that the action of the conductor remains perfect.
A second important cause for inspection lies in the necessity of always ascertaining with accuracy whether the earth connection is really in a faultless state. The immense significance of the earth connection—the basis, in more than one sense, of lightning protection—having been dwelt upon in the preceding chapter, it is only necessary here to state that, even if perfectly secured at the outset, it is liable to disarrangements. One not infrequent accident causing them is a change in the soil from moisture to dryness, which may be brought about either by altered drainage or long absence of rain. The dangers which threaten a break in the earth connection by altered or improved drainage are of the most serious kind, and likely to become more so from year to year. Not only the soil of our towns and cities, but even that of our villages, and the fields themselves, is getting ever more honeycombed by drain-pipes, until almost every drop of moisture is sucked out of the ground. No doubt the pipes themselves may improve the earth connection, if of iron or any other metal. But very frequently they are of earthenware, in which case they are far more dangerous than useful, even if filled with water. To guard against the danger likely to arise from changes in the drainage, it would be wise to have a thorough examination, by means of the test galvanometer, of all lightning conductors near to or affected by alterations in the drains, whenever completed. The same recommendation may be made as regards cases where the soil has become unusually dry after a long absence of rain. Few persons, except those who have made a study of the subject, can form an idea to what depth such dryness often extends, more especially in sandy and gravelly soils.
There is a third ground, as material for consideration as each of the two preceding ones, upon which the regular inspection of lightning conductors must be strongly urged. It is, that constant alterations in the interior of buildings, private residences as well as public edifices, may serve to destroy the efficacy of a conductor which was originally good, even to perfection. Thus a roof may be repaired, and lead or iron introduced where it was not before; or clamps of iron may be inserted in the walls of houses, to give them greater strength; or, in fact, any changes may be made which bring masses of metal more or less in proximity to the conductor. Under such circumstances, the efficacy of the conductor is destroyed just in proportion as the metal forms a better path for the dispersion of the electric force than the one artificially prepared. There are hundreds of instances to prove that changes made in buildings, such as the addition of a leaden roof without, or the iron balustrade of a staircase within, diverted the current of the electric force from the conductor on its way to the earth, originally well provided for. In one rather curious case, which happened at Lyons not many years ago, even an alteration of the fixtures of a house proved destructive to the efficacy of a conductor, perfect at the outset, the latter fact being shown in that it had previously received a stroke of lightning and brought it harmlessly to earth. The case was that of a banker possessed of the piece of furniture indispensable to his profession, namely, a large iron safe. It stood at first near an inner wall, in the centre of the house; but wishing to add to its strength in resisting the attack of burglars, the banker had it embedded partly in another wall adjoining that on the outside, near a place where the masonry was held together by some large iron clamps. In delightful ignorance of the effect of this removal of his safe inside the house upon the lightning conductor outside—an ignorance which would have been the same, probably, among 999 persons out of 1,000—the banker sat quietly down to dinner with his family one day in July, when a terrific shock made the whole house tremble to its foundations, upsetting furniture and breaking glasses. The idea of an earthquake naturally came up at once; but when looking out of the window (shivered to pieces) the banker was told by a crowd assembled outside that there had been no earthquake, but that his house had simply been struck by lightning, as it had been before. But while previously the electric force had passed silently into the ground, unknown even to the inmates of the house, and its passage verified only by the accidental observation of a neighbouring meteorologist, it had this time left its appointed path, seeking a new road more strongly attractive. The lightning had found its way into the banker’s safe, filled with gold. Once inside, the electric current, not finding a farther outlet, had expended its force in shattering the walls and making the house tremble, besides melting some gold and burning banknotes. The investigation of the case at the time made some noise, but it had one most useful result—it led to the institution of a new office in connection with the Department of Public Architecture of the city of Lyons, that of an inspector of lightning conductors. He was charged to examine at stated intervals, or as often as circumstances seemed to require it, the conductors applied to all the public buildings of the city, to ascertain their efficacy, and, if not deeming them in good condition, to effect all necessary repairs. Shall we repeat, again and again, ‘They manage things better in France’?
The regular inspection of lightning conductors, as yet unknown or all but unknown in England, has been for a long time in practice in several States of Continental Europe, among them Germany and France. The origin of such inspection may be traced to Northern Germany. It has been mentioned before (Chap. IV., page 43) that the first lightning conductor set up over a public building in Europe was erected on the steeple of the Church of St. Jacob, Hamburg, and that the extension of conductors in the city and neighbourhood was so rapid, that before five years had gone by there were over seven hundred conductors. ‘To this day they are comparatively more numerous in this district than anywhere else in Europe.’ To this day, too, the scientific aspect of the question of lightning protection, and the statistics connected with it, are more appreciated here, and have been more closely investigated, than in any other part of Europe. In recent years, this has been more particularly the case in the territories to the north of the city of Hamburg, the German province of Schleswig-Holstein. Not even in the country of their origin, and the one which, as yet, has the greatest number of them in use, have the ‘Franklin rods’ given rise to so much serious study as in that part of Germany.
Thunderstorms are more numerous, on the average, in Schleswig-Holstein than in any other part of Central and Northern Europe—due, probably, to the fact of the province not only being a narrow peninsula, with the Baltic on the east, and the German Ocean on the west, but intersected by rivers and canals, producing a generally moist atmosphere. Almost all public edifices in the province, and the great majority of private buildings above the rank of mere cottages, are protected by lightning conductors; and to aid in their extension there are special laws under which damages by lightning are not made good, except to a limited extent, by fire insurance companies, unless it is proved that the edifices struck had been provided previously with efficient conductors. These laws gave rise to a curious investigation some three or four years ago. It was found that the principal fire insurance office—an institution under the patronage of the Government, called the ‘Landesbrandkasse,’ or ‘County Fire Insurance Office’—had been called upon a number of times to pay for damage caused by lightning in cases where the buildings were provided with lightning conductors of the best kind, in apparently perfect condition. Though the cases were very few indeed—namely, but four out of 552 claims for damages from lightning which had been made in the course of eight years—still, the interest taken in the subject was so great, that the managers of the institution appointed a special commissioner to inquire thoroughly into the matter as to how it could happen that buildings provided with proper conductors could ever be struck by lightning. The gentleman chosen to undertake this task was Dr. W. Holtz, of Greifswald, well known as having given much time to the study of the phenomena of electricity, as well as the construction of lightning conductors. Dr. Holtz in due course made his report, which was afterwards published in a scientific journal called ‘Nachrichten des Naturwissenschaftlichen Vereins für Neuvorpommern und Rügen,’ being the organ of a society under the latter title. The report—which must be completely unknown in this country—is full of interest, and well deserves being extracted from in several notable particulars.
Dr. Holtz begins his report by referring to the well-known fact, already dwelt upon, that in some instances lightning conductors have got into disrepute because houses provided with them have been struck and damaged. ‘Unhappily,’ he says, ‘there are still at the present moment many persons who question the utility of conductors, simply because it happens now and then, that lightning, apparently in entire disregard of them, falls upon dwellings. These persons completely overlook two facts, namely: first, that such cases are excessively rare; and, secondly, what is far more important and more to the point, that it is beyond dispute that whenever buildings nominally provided with conductors are struck by lightning, these conductors are not in an efficient state. Such buildings are absolutely in the same condition as if they had no conductors at all.’ Dr. Holtz then goes on to speak of his journey of inspection to inquire into the causes of failure, or so-called failure, of lightning conductors. He says that, having examined a vast number of conductors, he found that in a good many instances real use had been sacrificed to ornament. He expresses this somewhat quaintly, in scientific style, apparently with the intention of not giving offence to anybody—not even to manufacturers of lightning conductors. ‘It was found by me,’ Dr. Holtz states, ‘that the unreal was frequently placed above the real, and that many lightning conductors, although very costly in the first instance, afforded no certain protection.’ The meaning of this clearly is, that too much attention is given to the upper part of conductors, especially the pointed top—frequently covered with needless gilding—and far too little to the part underground, forming the all-important earth connection. It is a criticism true for other countries besides Germany.
Among the many interesting remarks of Dr. Holtz, evidently based on a thorough knowledge of the subject which he treats, are some good ones about the necessity of constructing lightning conductors, not slavishly after old models, but in conformity with modern requirements, carefully considering the nature of the buildings to be protected and their materials. ‘The increase of metals,’ he says, ‘in the construction of houses, both inside and outwardly, is assuming larger proportions from year to year. An absolute consequence of it is, that the electric force called lightning is tempted, far more than was the case in older dwellings, not to go to the conductor at all, or, if attracted to it, to leave the path afterwards, seeking other attractions. I found this to have been the case, in the course of my investigations, in several instances, two of them notable ones. The first was that of the public school of the town of Elmshorm, struck by lightning away from the conductor; and the second that of the church of St. Lawrence, in the town of Itzehoe, where the conductor was struck at first, but the lightning deviated subsequently from its metal path. In both cases I found that the non-efficacy of the conductor was caused by a number of gas-pipes. But there are many other metallic masses besides gas-pipes which interfere thus with the proper action of lightning conductors. More or less, all metals do so, especially those which lead to the ground, or are in contact with moisture. Water-pipes will attract the electric force even more than gas-pipes, and likewise the metal tubes which carry the rain from the roof into the ground. But it may also happen that mere ornaments on the roof, more particularly if of thick metal, and carried all along the top and sides, may divert the electric force from the conductor, although they have no connection whatever with the ground. Even the many wires outside and inside houses, for bells and other purposes, may do mischief. There can be no doubt whatever that the large increase of the use of metals in the construction and ornamentation of modern houses has led to far greater danger to which they are exposed from lightning. At the same time there is equally little doubt that all this increased danger may be absolutely guarded against by the setting up of lightning conductors by competent persons, carefully designed to meet all cases.’ Dr. Holtz adds, further on, that one most important element of protection to be obtained from conductors consists in the regular testing of them, without which, indeed, there can be no permanent security.
What the writer says on the inspection of conductors is particularly worth quoting. ‘A lightning conductor,’ he remarks, ‘however excellent in the first instance, may lose all its good qualities, for several reasons. In the first instance it may suffer, like all mundane things, from age. The decrepitude will come on all the sooner whenever the materials are not of the best kind, or whenever little care has been taken in properly connecting the various parts. This is frequently the case in conductors of old design. But, even if all has been done that scientific skill can accomplish, age will make itself felt some time or other. Oxidation will play its part; so will the warfare of the elements. However safely secured at first, the attachment of the parts to the buildings will get loose, or perhaps even broken. Repairs consequently become indispensable. When are they to be effected? It can only be indicated by testing the conductor from time to time.’ Dr. Holtz next dwells at some length on the necessity of conductors being designed by thoroughly competent persons; not mere ‘lightning rod men,’ who are able to take into account all the particulars of the building which is to be protected, more especially the metal employed in the construction. ‘A conductor,’ he truly remarks, ‘cannot be expected to be a trustworthy protection against the destructive force of lightning, if simply set up over a house without consideration of its outer and inner features. Perhaps in buildings of olden times, into the construction of which metals seldom or never entered, a simple wire running from top to bottom, surmounted by an iron rod, was quite sufficient, but this is no longer the case, all the circumstances having been completely altered. The wire, however thin, was not merely the best, but the only path for the electric force. But at present the masses of metal used in the construction of buildings constitute a number of rival paths, and it requires very careful consideration indeed to lay down an absolutely infallible lightning conductor in such a way as to overcome all influences opposing its action. Therefore conductors of old construction can not only not be expected to be efficacious under modern exigencies, but even those made at the present time cannot be expected to be efficient under circumstances which, probably, the future may bring forth. There is really nothing else to make a lightning conductor a safe protection under all circumstances, and at all times, but regular, constant, and skilful examination.’