THE THUNDER STROKE.
THE question was asked in the Spectator of June 18th whether it was worth while for a householder to protect his building with lightning-conductors, and we think that Mr. .Alfred Hands, in a little book just published, "Lightning and the Churches" (J. W. Gray and Son, 91 Leadenhall Street, E.C., Is. net), gives a very good answer to the question. He has collected into some ninety pages a large number of instances of the effect of lightning, and without trying to fit the facts to his theories, he manages to make out a case worth careful study, both from the scientific point of view and that of the mere calculator of pounds, shillings, and pence. The damage done by lightning, in England and Wales, as regards which countries Mr. Hands has occupied himself in collecting information, is probably more extensive than most people would believe. Mr. Hands has compiled a chart showing the places known to have been struck in the years 1897-1908, and on the chart he has had to mark 7,793 different spots, and to chronicle damage done to 211 cathedrals, churches, and chapels; 3,190 other buildings of various kinds ; 226 ricks and stacks ; 1,251 trees, and 398 other objects ; while 194 persons have been killed and 1,016 injured, and there have been 1,307 cases in which animals have been killed, these being either single creatures or several killed by one stroke. There have been as many as 49 sheep struck dead in a single flock. The monetary loss is estimated at £50,000 to £100,000 per annum, but obviously the "moral and intellectual" damages are the more serious.
What, then, is the tremendous force which does all this mischief P We need not go into abstruse considerations of the nature of electricity, or the composition of the ether, but we can examine some of the effects which are produced by the ether in motion or under stress or strain. From the latter we get static electricity, and the ether in continuous motion produces current electricity. Current electricity, Mr. Hands remarks regretfully, is the only kind which is much studied,—naturally, perhaps, since it is the electricity of com- merce. He, however, is a student of static electricity, and his explanation of what happens when an object is " struck " by lightning may be given in his own words :—" When a thunder- storm occurs a stress is thrown on the air, either between two clouds or between a cloud and the earth, and when this stress has reached a pressure of about half a gramme weight to the square inch, smash goes the air—it is literally cracked. The line of the fracture is illuminated by the intense heat caused, rendering the air particles incandescent, and we see this and call it lightning. This is all lightning is ; there is no bolt,' and no transference of matter from one place to another. To speak or write of an object as being `struck' by lightning is calculated to produce a wrong impression, because it conveys the idea of a ponderable object giving a blow. It is literally an incorrect term, but we are forced to employ it because it has been so long in use." Perhaps the incorrectness of the word can be better understood when we realise that when there is a flash of lightning the air is just as mach " struck " as the other objects through which the flash passes,—a church- steeple, for instance, or a tree, or a human being. What happens in each case is the same : the lightning is finding its way by the path of least resistance. It runs through the weakest substance near, just as paper is torn at its weakest points, or as a river winds its way to the sea. The stronger substances withstand it, and the weaker substances give way. When the air is cracked, then the lightning makes its path by the weakest component parts of it,—those parts, for instance, which contain moisture; that is why the flash is seen to take a sinuous course. But air, as a fact, is relatively very strong as regards 'lightning, while other substances, which we think of
as strong, are to lightning very weak. Metal is weakest of all; a human being is stronger than metal, and masonry or wood is stronger than a human being. So that a lightning- flash occurring in the neighbourhood of a wall or a tree and a man would choose the man rather than the wall or tree, and would leave either of these for a path of metal.
That, then, is the principle of the lightning-conductor, and we do not regard the conductor rightly if we think of it as " attracting " lightning. A conductor no more " attracts " lightning than a bank of sand attracts a stream which must either pass through the sandbank or a wall of rock. And, as Mr. Hands points out, we should none of us be so foolish as deliberately to attach to any building an instrument designed to attract lightning. As a matter of fact, the point of a con- ductor actually dissipates electricity, and to a certain extent can be said to prevent an electric discharge. On dark nights during thunderstorms you can see the point of a conductor glowing with the pale light known as "St. Elmo's fire," and sailors are familiar with the lights which play on mastheads, yardarms, and other pointed parts of vessels. A very interest- ing example of the effect upon lightning of the presence of points is the Temple of Solomon. Josephus tells us that the roof was ornamented with points covered with gold ; the points, probably, were intended to prevent birds from settling and so soiling the roof. But the unintended effect was that the Temple was perfectly protected from lightning, and in a country in which thunderstorms are severe and frequent it stood undamaged for a thousand years. When the Roman Emperor tried to rebuild it, leaving out the points and the gold, it was " struck " at once. If, then, we ask why lightning- conductors do, as a fact, get struck, the answer is that the point has not sufficient time to dissipate the electric discharge. The cloud charge above and the earth charge below are developed towards each other so rapidly that the point cannot keep pace with the accumulation, and so the charge rushes along the conductor. But the result, if it touches nothing but the conductor, is satisfactory enough.
How does it happen that churches and buildings are struck when they have lightning-conductors fixed to them P Mr. Hands meets the question squarely. Generally speaking, he answers that the conductor has either been improperly affixed, or has been allowed to get out of repair. He has investigated case after case and found that conductors placed on buildings that have been struck have rusted away or have been broken, or have originally been affixed by men wholly ignorant of main principles. A conductor could be made, for instance, to act as a passage-way from one piece of metal in the church to another. Mr. Hands shows by diagrams and photographs how lightning will jump, as it were, from one piece of metal to another in its passage down an un- protected church-tower, and how, in a tower "protected" in an unscientific way, the discharges may prefer some other path to the conductor,—if, for instance, the conductor has a bad earth connexion. On the other hand, he gives instances of churches, such as Week St. Mary in Cornwall, and St. Botolph's, Boston, Lincolnshire, better known, perhaps, as " Boston Stump," which were struck time after time till a conductor was fixed, and which have not been struck since. Then again, as he points out, we do not know how many times churches which are protected by conductors have been struck without being injured, for the only way in which you can tell whether a conductor "has been put to the supreme test and has saved the building from damage " is by a slight mark of fusion at the tip. It is a common occurrence, we learn, to find these marks when inspecting conductors. It would be rather exhilarating to discover the traces of fusion on one's own lightning-conductor. But, to sum up the question of the value of conductors generally, could anything be better than the argument, not of the house, but of the battleship P In the old days of masts and sails the wooden ships were continually being struck. Now, with ships of steel, the crew live in a vast floating conductor, and steam through a storm more safely than if they were walking on dry land.
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