CHAPTER XII.

LIGHTNING PROTECTION IN FRANCE AND AMERICA.

In this chapter it is proposed to give a brief _résumé_ of the different systems of constructing, erecting, and repairing lightning conductors in France and America. The laws of electricity being the same all the world over, the methods employed in these countries are necessarily similar in their essential principles; nevertheless they vary somewhat in detail, both from each other and from the work of the best firms in England.

Until a very few years ago the lightning conductors throughout France, although many in number, were in a very neglected state. Badly constructed in many cases, their original faults had grown worse from want of attention. The connection of the terminal rod with the conductor was generally made by means of a strap or iron collar, which, after a short time, rusted to such an extent that the continuity was practically reduced to nothing, and the conductor, so far from being a protection to the building, was a positive danger to it.

Latterly, however, a reaction has taken place, and a more careful method of connecting the various joints of the conductor has been contrived, or rather, revived, and a better system of periodical inspection and testing is carried out.

Under the French system, what is called in England a lightning conductor, and to which the French give the name _Paratonnerre_, is nominally divided into three parts: the terminal rod, the conductor, and the _racine_, or root, i.e. the earth connection. With regard to the terminal rod, the ‘area of protection’ theory is, in France at any rate, still believed in by a great many people. In that country, as a rule, it is made of wrought iron in a single length, and polygonal or slightly conical; its height depends upon the size and area of the building it protects, the general presumption being that, under ordinary circumstances, a terminal rod will protect effectually a cone of revolution, of which the apex is the point of the rod, and the radius of the base a distance equal to the height of the said rod above the ridge, multiplied by 1·75. Thus a rod rising eight yards above the ridge of a building would effectually protect a cone-shaped space, the base of which, at the level of the ridge, has a radius of 8 × 1·75 = 14 yards. In actual practice somewhat wider limits are allowed. The height of the terminal rod having been determined according to the circumstances under which it is erected, it is then galvanised with zinc in order to prevent oxidation, and the connection between the terminal rod and the conductor is formed by means of the following arrangement. A little above the base of the terminal rod, say about eight inches from the roof of the building, a flange A (see fig. 10) is welded with a hole pierced through it. Through this hole the conductor, previously filed down to the proper dimensions, must be tightly passed. After scraping the iron around the hole, a washer of lead is placed at P and P´ (see fig. 11), and the button B, by means of a strong layer of solder, thoroughly binds everything together. In this way an excellent joint is obtained; the contact surface is considerable, and, if the work is carefully done, the joint is completely preserved from rust.

The point of the terminal rod, although sometimes made of platinum, generally consists of either pure red copper, or, what is considered still better, an alloy of 835 parts silver and 165 parts copper. It is fastened to the terminal rod in the manner shown in fig. 12.

C is the trunk of a red copper cone, upon the top of which a point, P, made either of platinum or of an alloy of silver and copper, as before mentioned, is screwed, pinned, and strongly soldered with pewter solder at _a_, the whole being screwed on to T at _b_. To ensure complete contact and continuity, a washer of freshly-scraped lead is inserted between C and T, and the whole of the joint thickly covered with a layer of pewter solder. It may be added that the point forms an angle of fifteen degrees with the vertical, consequently the point terminates in an angle of thirty degrees.

For the conductor of the ‘paratonnerre’ lengths of iron bars are principally used; formerly these were jointed together by means of a pyramidal bolt let into a notch of the same form, and connected by a simple iron pin. This method, however, was discovered to be very bad, as it failed to preserve the continuity of the conductor after it had been erected a little time. The following plan, as represented in fig. 13, is now used for the best work, as being more durable and affording a better contact. On each side of the bars to be joined, two flanges, about six inches long, and half the thickness of the bars, are filed out. A thin piece of carefully-prepared lead is then placed between them. The whole is then firmly fastened together by bolts at B and B and completely covered with pewter solder, and thus furnishes a solid, durable contact which possesses very small resistance.

Formerly the conductors were, at regular intervals, rivetted to cramps let into the wall for the purpose of retaining the conductor in its place. As this plan left no room for the play of expansion and contraction caused by variations in the temperature, it was found that at times the conductor was very much strained and even bent by reason of this expansion and contraction. To avoid this evil an apparatus, which has been approved by the Paris Academy of Sciences, has been substituted for the cramps and rivets. This apparatus consists of a fork in which the conductor is held fast by a pin (see fig. 14). Being able to move backwards and forwards in the fork with great facility, the conductor is thereby permitted to expand or contract under the influence of temperature without threatening its supports with destruction.

The question however arises, upon what part of the paratonnerre ought the effect of such contraction or expansion to be borne? The Paris Academy of Sciences has sanctioned and recommended the use of a compensator, which is designed to bear this strain. This compensator, which is now much used in France, may be seen in fig. 15. It is composed of an elastic plate F, made of well-annealed red copper, three-quarters of an inch wide, at least twenty-eight inches long, and about a quarter of an inch thick. The two extremities of this plate are firmly fastened to the two ends of two lengths of the conductor by the bolts and counterpieces B B´, and afterwards covered with a thick coating of pewter solder. When, in consequence of the heat, the conductor expands, the curve of the copper plate F will become greater, and in cold weather it will become less. As a rule, a single apparatus is supposed to compensate for the effects produced by long straight lengths, and it is therefore thought sufficient to place one at each bend.

With the exception of the terminal rod, it is the rule in France to cover the whole of the paratonnerre with some coating in order to preserve it from contact with the air. This is attained by covering it with either a strong coat of tar, or a painting of a metallic basis, such as zinc or tin filings.

In larger buildings what is termed a ‘ridge-circuit’ is often used. It consists of an unbroken metallic connection running along the ridges of the building to be protected, and connected with the conductors and terminal rods, and consequently with the subterraneous sheet of water which forms the common reservoir. It is made of lengths of square iron bars or rods having a thickness of about three quarters of an inch square, and fastened together by overlaying the ends, bolting them together with two bolts, and covering them well with solder in the manner shown in fig. 13. New branches are formed by T-shaped connections, the cross-piece of the T overlaying the original ridge-circuit, and the stem making the first length of the new branch. In some cases the ridge-circuit rests directly on the ridge of the roof; but in order to avoid injury during the repairs to the roof or in other ways, the plan adopted in good work is to raise it some distance above the ridge on supports at suitable distances, and thus prevent the possibility of damaging the joints and solderings.

The form and arrangement of these supports depend on the nature of the roof. Sometimes forked uprights are used--these allow for the expansion and contraction due to changes of temperature; in other cases simple cast-iron bearings, weighing from ten to twelve pounds each, are laid upon the ridge, their upper surfaces being grooved to receive the bars of the ridge-circuit.

All masses of metal used in the construction of the building are metallically connected with the paratonnerre. As a rule, this is done by pieces of iron about half an inch square, which are strongly soldered to the metal surfaces, and then connected with some part of the conductor or ridge-circuit.

Although in France, as elsewhere, all experts are agreed as to the prime importance of the disposition and arrangement of the _racine_ or earth-end of the paratonnerre, a difference of opinion prevails as to the best means of insuring a good earth-contact, and many methods have been tried, all of them similar in principle, but differing somewhat in application. It is proposed to give here a brief outline of the best contrivances employed for this purpose.

One main object, in arranging the earth terminal of a lightning conductor, is to avoid the gradual destruction of the _racine_ by the action of alternate dryness and moisture which, unless the iron is protected in some way, corrodes, and eventually eats it entirely through. There are several ways of remedying this evil. In France it is common to find used for this purpose a vertical spout of tarred, boucherised, or creosoted wood, rising a few inches above the soil. Some authorities recommend the simple plan of covering this part of the conductor with a strong coating of tar, others covering it with a wrapper of sheet lead, and this last method is probably the best. With regard to the extreme end of the conductor, the system approved of by the Paris Academy of Sciences is generally used in good work. This system is the use of a trough filled with broken charcoal, through which the conductor runs; charcoal preventing the too rapid oxidation of the iron. For charcoal, coke may be substituted. The trough (see fig. 16) is made either of wood, gutter tiles, or ordinary bricks without mortar, so as to allow the moisture of the soil to permeate through. It is preferable, even at the expense of lengthening the conductor, to carry it through the lowest and dampest plots of ground around the building.

To obtain a perfect contact between the end of the conductor and the earth, or common reservoir, the French use several methods. One of the earliest ones was the multiplication of the iron bars attached to the end of the conductor, and inserting them for some distance into well-water. Theoretically this arrangement is good, but it has been found that the decay of these terminals by the action of rust was so rapid that, unless they were carefully watched and periodically repaired, they soon became insufficient, if not useless. In addition to this, it is the opinion of many French savants that a mere water contact is not enough, a soil that is always moist being in their judgment far preferable. The simplest plan adopted for attaining this end is that of inserting into the moist ground to a certain depth, regulated by the nature of the soil, one or several metallic branching stems, which are connected with the conductor. By another arrangement, invented by M. Callard, the conductor is terminated by a kind of galvanised iron grapnel, placed in a wicker basket filled with pieces of coke. Where the soil is dry, and moist ground cannot easily be got at, the harrow or grating shown in fig. 17 is often used. It is placed between two layers of horn embers, or charcoal, and sunk as deeply as it conveniently can be, the end of the conductor being carefully connected with it by soldering or by a quantity of melted zinc.

In towns, the water-pipes and gas-mains, possessing as they do, large metallic surfaces, are generally utilised for making the ‘earth-contact.’

Sometimes, instead of iron bars, galvanised iron cables of about an inch in diameter are used for the conductors of paratonnerre, and occasionally red copper cables of half-an-inch only in diameter, but the use of these latter is uncommon.

Fig. 18 exhibits a modification of the point of the terminal rod which is advocated by M. R. F. Michel. The arrangement is based on the principle that, on the approach of a tempest cloud, the more points there are, the greater will be the neutralising effect. M. Michel considers that when a terminal rod has only one point, it acts only in one direction; but if there is a large number of points branching in all directions, the preventive action is materially increased; he therefore proposes the use of this contrivance, which is carried out by having the ordinary conical trunk copper point on the top of the terminal rod melted down, and moulded so that it presents in its middle a circular swelling. Into this swelling arrows are fixed, inclined at each side of the horizontal plane to an angle of 45 degrees, as shown in the engraving. These arrows radiating in all directions are supposed to ‘hasten the neutralisation of the electrified cloud; and in the event of a discharge, the discharge, by dividing amongst them, will prevent their fusion.’

Before quitting the French system, mention should be made of a novel form of lightning conductor devised by M. Jarriant. This gentleman proceeds on the hypothesis that the most essential requisites of a lightning conductor are:--a terminal rod metallically homogeneous, which should rise to a good height; that it be sufficiently light to avoid damage to the roof, and yet be strong enough to resist the violence of the wind. To attain these requirements, M. Jarriant secures his conductor with three or four stays, which are firmly fixed to the roof and converge to the top of the terminal rod, to which is fastened the ordinary copper point, recommended in the ‘Instruction’ of the Academy of Sciences. Iron supports are placed at different heights in order to ensure the perfect solidity of the system. Galvanised iron is employed, and all the various stays and supports are metallically connected with each other. The angles of the irons are all acute, and placed so as to offer the least resistance to the wind. The advantages claimed for this method are that the upper part of the conductor bristles with spikes and aigrettes, which he considers a great advantage in regard to the preventive effect produced by the conductor; it allows of the conductor being raised much higher above the building; it presents a large surface to the electrified cloud; the joints are so arranged that they cannot be dislocated by the expansion and contraction caused by variations of temperature; and, lastly, it is affirmed that these conductors cost thirty per cent. less than those erected under the ordinary system.

America stands pre-eminent above other countries in the numerous and extraordinary schemes that have there been promulgated in regard to the protection of buildings from the effects of lightning, and probably no other nation has been so systematically victimised and swindled in this matter. The tramping ‘lightning-rod men’ of the United States are notorious for extortion and ignorance: they use all kinds of fantastic and peculiar shaped terminal rods and conductors, the main object being to make as great a show with as little metal as possible. Their work is almost entirely confined to the upper portion of the conductor, to the neglect of the most important part--the earth terminal. In consequence, the majority of the lightning conductors in America are untrustworthy; very often they are practically insulated from the ‘common reservoir’ or subterraneous water, and are therefore more often a source of danger than a protection. Unhappily, these peripatetic mechanics are by no means extinct, although increased knowledge is gradually driving them from the field.

In America, a strong point is made of utilising, as far as possible, all the existing natural conductors that are to be found upon a building, such as gutters, rain-pipes, and other metal surfaces. During a tempest, the opposite electricities of the earth and the air often select, by their inductive influence, a rain-pipe, gutter, metal roof, &c., for the passage of an electric discharge between them, and unless these metallic surfaces are connected with the earth, they are apt to be dangerous. But if they are properly connected together, and provided with a good earth-contact, they materially assist to diminish the intensity of a discharge.

In the case of a building with a roof of slate, wood, or other material of low conductivity, a conductor made of either bar iron or stranded cable is placed along the ridge and gable ends, and carefully connected with the gutters and rain-pipes; where the rain-pipes are less than three inches in diameter, the bar or cable conductor is often extended from the roof down the side of the building, and connected with the earth terminal. When this is done, the bar or cable conductor is placed between the rain-pipe and the wall of the building, or at any rate close to the rain-pipe, and connected with it by solder or bolts.

All metallic chimney caps, cornices and railings on the tops of buildings, as well as the water-pipes, gas-pipes, hot water-pipes, and other large or long pieces of metal, whether they occur inside or outside the building, are connected with each other by a conductor composed of light stranded wires, each about three-sixteenths of an inch in diameter; they are also connected with the main conductor at its nearest point. Where several adjacent buildings have each a metallic roof, these roofs are connected together by means of a horizontal conductor.

The terminal rod of the conductor generally projects about four feet above the chimney or other highest point of the building. It consists of a round iron rod seven-sixteenths of an inch in diameter, the lower extremity being hammered out for the purpose of fastening it to the conductor by soldering and screws or by bolts. A small building, not exceeding twenty-five feet in length or breadth, is generally fitted with either one terminal rod placed on the centre of the ridge of the roof, or with two rods, one at each end of the ridge, the latter method being the preferable one. In larger buildings terminal rods are placed at intervals of about twenty feet along the roof. The upper end of the rod is sometimes pointed, but not always, the argument being that although the ordinary end of a rod is blunt when used in connection with a Leyden jar, but that when applied to a thunder-cloud, which extends over thousands of acres, it becomes pointed, and bears the same proportion to a thunder-cloud as the sharp point of a needle does to the hand of a man. Occasionally the point is tipped with platinum, gold, silver, or pure copper, in order to prevent oxidation, but this is not considered essential, it being presumed that, practically no amount of rust on the top would impair the efficacy of the terminal rod.

In the case of a building having a flag-staff upon it, a galvanised iron wire is fastened along it and projects about six inches above the top, the lower end of the wire being of course carefully soldered or otherwise connected with the main conductor.

Steeples and spires, in addition to the ordinary vertical conductor, are fitted with horizontal conductors placed around them at intervals of about twenty feet, and connected with the vertical conductor. This is to provide against the occasional discharges that take place in the centre of steeples, and which are caused by the deflection of the discharge in the air by the rain.

Chimneys and air shafts, from which heated air or smoke escapes, are fitted with metallic caps which are connected with the general conductor. In order to protect this metallic cap from the effects of the sulphurous fumes arising from the chimney, a terra-cotta cap is contrived to fit inside the metallic cap. An analogous method is adopted with regard to the ventilators of barns and ice-houses. If these buildings have the ordinary ventilators in the form of dormer windows upon the roof, an iron rod seven-sixteenths of an inch in diameter is placed vertically across, and above the centre of the opening of each ventilator, and connected with the conductor. Should the barn or ice-house have openings or doors through which warm vapour can escape, a conductor is fixed to the roof at the gable ends above the centre of each opening or door, and extended outwards about five feet, at an angle of forty-five degrees from the roof, so as to be in line with any ascending vapour, or any descending charge of electricity following the course of the vapour. All these auxiliary conductors and terminal rods are metallically connected with the main conductor of the building.

The conductors are simply fastened to the building by iron staples or by straps of sheet iron, pierced with two holes for nails or screws.

In America, as elsewhere, the earth-terminal is regarded as of prime importance, and in all properly constructed lightning conductors receives the greatest care and attention. In the first place, such metal pipes as lead from the building to the water-mains, gas-mains, and sewers are carefully connected with the principal lightning conductor, in order that they may act as auxiliary earth-terminals. For the principal earth-terminal many contrivances have been brought forward, but very few possess any originality, and many are positively useless. Some of the best are similar to those in use in England; among others, perhaps the best method is that of placing a cast or wrought-iron pipe of three inches inside diameter, and about ten feet long, vertically in thoroughly moist earth and carefully connecting the conductor, or conductors, with it. The chief objections to this plan are the occasional difficulty of getting a moist earth at all, and the possibility of earth that is generally moist getting dried up in hot weather. To obviate these risks, the following arrangement is used:—

In a pipe of wrought or cast iron, at least ten feet long, and having an inside diameter of two inches with a thickness of three-eighths of an inch, are made a number of longitudinal openings or perforations, about ten inches long and a quarter of an inch wide. These openings or perforations are made at intervals of ten inches, and are placed in one or two lines opposite to each other. If it is preferred, round holes of from half an inch to one inch in diameter, and about six inches distant from each other, may be substituted for the longitudinal openings. This perforated pipe is placed in an upright position in the earth, and is so situated that it receives at its top opening the waste or rain water flowing along a channel or drain constructed for that purpose. The water, after running into the top of the pipe, gradually percolates down, and passing through the perforations or openings into the earth around and underneath the pipe, moistens it to such an extent and at such a depth as to render it but little affected by the heat of the sun. The pipe is generally placed at some little distance from the building, so as to give a sufficient area of earth to be kept moistened and to prevent the walls of the building being affected by the damp.

Occasionally, the pipe is made triangular or square, and with perforated branches and other metallic conductors. It is also sometimes constructed with enlargements at the top or bottom, so as to hold more water. Probably, however, the simplest plan is the best, as--if the soil be suitable--a plain round wrought-iron pipe can be driven into the earth. If a cast-iron pipe is used, a hole of a convenient size is excavated for it. In this case, great care has to be taken that the earth is thoroughly well rammed down all round the pipe.

Another arrangement is to employ, instead of a cast or wrought-iron pipe, a number of round or flat-iron bars, fastened together at the top and bottom by rivetting to metal hoops in such a manner that intervals are left between each bar, through which the water can pass. Sometimes a solid pipe without the openings is used, but it is not found to be so satisfactory as the perforated pipe, because the latter allows a greater amount of water to pass through it into the soil, thereby furnishing a larger area of moist earth.

The French method of carrying the conductor to the bottom of a neighbouring well is frequently adopted where it is practicable, and the water of the well is not required for drinking or cooking purposes.

A few words may be added here on the method of protecting the large mineral oil tanks which are to be found in the United States. Many of these oil tanks are of very large capacity, some of them containing a million gallons of oil. They are generally constructed of thick iron plates rivetted together. The roofs are usually made of wood coated with tar, but in some cases iron is adopted. As a rule, several of the tanks are grouped together and connected with each other--and in some instances with distilleries--by means of subterraneous iron pipes.

One method of protecting these tanks is to erect around them, at a distance of some ten feet, wooden supports, on which are placed upright metallic conductors which overlook the tank, and are connected with each other near their tops by stout iron wires, thus forming a network of conductor which is supposed to intercept any discharge of electricity from a tempest-cloud, and prevent it from reaching the oil tank. This method, however, has failed in several notorious instances, and is not countenanced by the best authorities.

A better and less complex arrangement is now usually adopted by the best firms. The chief object of this arrangement is to prevent the temperature of the oil tank, and of the atmosphere above and around it, being raised by means of an electric discharge. This is accomplished by using large conductors, which are carried some distance above the oil tank. These conductors, of which there should be at least four, are formed of flat iron bars about one and a half inches wide and half an inch thick; they are securely fastened to the sides of the tank at equal distances from each other, and metallically connected with it. About thirty feet above the roof of the tank they meet, and are carefully and substantially joined together, and supported, if necessary, by a wooden post extending from the centre of the roof of the oil tank.

The earth terminals, of which there must be one to every two conductors, consist of perforated iron pipes, as before described, three inches in diameter and fifteen feet long. They are sunk into thoroughly moist earth, and metallically connected with the lower part of the tank. These perforated pipes are so arranged that they catch the rain water from the roof of the tank; by this means the surrounding earth is kept moist. It may be mentioned that by utilising the tank as a portion of the system of conductors, the electric discharge is distributed and much weakened.