Читать книгу Lightning Conductors - F.C.S. Richard Anderson - Страница 7

Table of Contents

The first actual lightning conductor ever constructed was set up by Benjamin Franklin himself, at his house in Philadelphia. Its main object was to protect the house against the effects of thunderstorms; still experiments were so dear to the heart of the great discoverer, that he could not help making trials even with things devoted to other uses. It was in the summer of 1752 that Franklin erected over his house a lightning conductor, made entirely of iron, but with a sharp steel point on the top, the latter projecting seven or eight feet above the roof, while the end was above five feet in the ground. Curious to know whenever an electrical stream was passing through the conductor, he attached to it an ingenious contrivance, by means of which through an electric spark two bells were set in movement as soon as this took place, the greater or lesser noise from them corresponding with the strength of the electrical current. With the aid of this device Franklin was enabled to observe some curious phenomena, which at first puzzled him not a little. ‘I found the bells rang sometimes,’ he informed a friend, ‘when there was no lightning or thunder, but only a dark cloud over the rod; that sometimes, after a flash of lightning, they would suddenly stop, and at other times, when they had not rung before, they would, after a flash, suddenly begin to ring; that the electricity was sometimes very faint, so that when a small spark was obtained, another could not be got for some time after. At other times, the sparks would follow extremely quickly; and once I had a continual stream from bell to bell, the size of a crow-quill. Even during the same gust there were considerable variations.’ By continued watching, Franklin came to make the discovery that the fluctuations in the electrical current were owing to changes and interchanges, in atmosphere and earth, of positive and negative electricity. He held at first that thunder-clouds are usually in a negative state of electricity, but afterwards discovered that they varied from negative to positive during the same storm.

Notwithstanding the unbounded praises bestowed upon Benjamin Franklin for the great discovery of the lightning conductor, the actual adaptation of it spread with extreme slowness. It was in the country of its origin that it was brought into public use, all the countries of Europe lagging far behind. But even in the Northern States of America, though inhabited by a highly intelligent race, there were great difficulties to overcome. The ministers of religion at first seemed to think that the iron rods were not altogether free from the suspicion of infidelity. Franklin himself had the reputation of being a free-thinker, and indeed never hid from others the fact of his being accustomed to examine all matters by the light of his own reason, and to believe nothing that he could not understand. Perhaps on the same ground many of the New England ministers did not believe in lightning conductors. They could not understand them. A heavy shock of earthquake was felt throughout Massachusetts in the summer of 1755, whereupon a Boston clergyman instantly came forward, denouncing in eloquent strains the erection of a number of lightning conductors which had taken place. The high iron rods, he gravely maintained, had been the cause of the earthquake, by drawing vast masses of electricity from the atmosphere into the ground. A distinguished friend of Franklin, Professor Winthrop, of Harvard College, thought it necessary to come forward and defend lightning conductors against the accusation of accumulating electricity, but without convincing the plaintiff. A different charge, still more serious in the eyes of pious people, had been made against lightning conductors some years before. Another Boston clergyman, coming forward in 1770, opposed the use of Franklin’s iron rods on the ground that, as the lightning was one of the acknowledged means of punishing the sins of mankind, and of warning them from the commission of acts of wickedness, it was impious ‘to prevent the execution of the wrath of heaven.’ To this gentleman also Professor Winthrop deemed it requisite to reply. Franklin himself remained silent, wrapping himself in the mantle of the sage. But he allowed his friend Ebenezer Kinnersley, of Philadelphia, who went travelling, by his wish and partly at his cost, through the principal towns and villages of the New England States, to explain to the people the uses and advantages of lightning conductors, to preface all his lectures by the announcement that the erection of iron rods to protect houses from the effects of thunderstorms was not an act ‘chargeable with presumption, nor inconsistent with any of the principles either of natural or revealed religion.’

In the gradual spread of lightning conductors through the British colonies of North America, Franklin himself took the leading part. He employed all his leisure time, engrossed though it was more and more by political affairs, in which he was destined to take a world-famous part, in going from one part of the country to another, advocating the use of conductors, advising as to the best mode of their construction, and, whenever he could, examining into the effects of strokes of lightning upon buildings. How minute he was in these inspections, and how practical in the conclusions he almost invariably drew from them, Franklin gives proof in one of his letters addressed to his friend Collinson in London. He tells him that he inspected the church of Newbury, in Massachusetts, which had been struck by lightning, and traced, foot by foot and inch by inch, the road which the electric current had taken, creating great havoc and destruction. ‘The steeple,’ he says, ‘was a square tower of wood, reaching seventy feet up from the ground to the place where the bell hung, over which rose a taper spire, of wood likewise, reaching seventy feet higher, to the vane of the weathercock. Near the bell was fixed an iron hammer to strike the hours; and from the tail of the hammer a wire went down through a small gimlet-hole in the floor the bell stood upon; then horizontally under and near the plastered ceiling of that second floor, till it came to a wall; and then down by the side of this wall to a clock which stood about twenty feet below the bell. The wire was not bigger than a common knitting-needle.’ It surprised Franklin that ‘the lightning passed between the hammer and the clock in this wire, without hurting either of the floors, or having any effect upon them, except making the gimlet-holes, through which the wire passed, a little bigger, and without hurting the wall or any part of the building.’ The inference he drew from this was, that even a comparatively thin mass of metal would give passage to a powerful electric stream. ‘The quantity of lightning that passed through the steeple,’ he informed his correspondent, ‘must have been very great, as shown by its effects on the lofty spire above the bell, and on the square tower below the end of the clock pendulum; and yet, great as this quantity was, it was conducted by a small wire and a clock pendulum, without the least damage to the building as far as they extended.’

Besides travelling and employing lecturers, to make the advantages of lightning conductors known, Franklin found means of doing so in an annual publication he had started in the year 1732, known as ‘Poor Richard.’ This almanac, humorous in form but very serious in substance, which had acquired an enormous circulation, proved in the end the most powerful instrument for spreading information on the great subject dear, above all others, to Franklin’s heart, and leading his countrymen to adopt, before all other nations, the wonderful metal rod, protective against ‘the wrath of heaven.’ In several of the editions of the almanac, notably the ‘Poor Richard’ for the year 1758, Franklin drew attention to his lightning conductors in simple advertisements, drawn up in a spirit of absolutely touching modesty and self-abnegation. Not seeking the slightest reward for himself, nor even mentioning his name, he only sought to benefit others by instructing them how to get protection against the dangers of lightning. ‘It has pleased God,’ ran the advertisement in the almanac, ‘in His goodness to mankind, at length to discover to them the means of securing their habitations and other buildings from mischief by thunder and lightning. The method is this:—Provide a small iron rod, which may be made of the rod-iron used by nailers, but of such a length that, one end being three or four feet in the moist ground, the other may be six or eight feet above the highest part of the building. To the upper end of the rod fasten about a foot of brass wire, the size of a common knitting-needle, sharpened to a fine point; the rod may be secured on the house by a few small staples. If the house or barn be long, there may be a rod and point at each end, and a middling wire along the ridge from one to the other. A house thus furnished will not be damaged by lightning, it being attracted by the points and passing through the metal into the ground without hurting anything. Vessels also, having a sharp-pointed rod fixed on the top of their masts, with a wire from the foot of the rod reaching down round one of the shrouds to the water, will not be hurt by lightning.’ Franklin had occasion subsequently greatly to modify the advice here given. He early discovered his error of lightning being ‘attracted by the points;’ and also found that his recommendation to people to construct their own lightning conductors only led to grievous calamities. There came reports from all sides of houses having been severely damaged by lightning notwithstanding having conductors, and close investigation soon showed that in every instance the apparatus was defective, having been erected by unskilful hands, either the owners themselves, or a set of wandering impostors, who soon made themselves notorious as ‘lightning-rod men.’

Having improved in various ways the lightning conductor set up experimentally over his own house, Franklin erected a second one, of larger dimensions, to protect the residence of one of his friends, Mr. West, a wealthy merchant of Philadelphia. The apparatus, constructed entirely under the supervision of Franklin, consisted of an iron rod half an inch in diameter throughout its length, and ending at the bottom in a thick iron stake, driven four or five feet into the ground. The top of the conductor, rising nine feet above the central stack of chimneys, was formed by a brass wire ten inches in length, tapering off in a sharp point. Franklin considered the brass wire, which was screwed and soldered inside the iron rod, a great improvement upon simple iron, having discovered brass, as well as copper, to be better conductors of electricity. The result justified his expectations. Not many months after the lightning conductor had been erected over the mansion of Mr. West, a thunderstorm more severe than had been experienced for many years broke over Philadelphia. Vivid flashes of lightning followed each other incessantly, one of them striking, visible to all beholders, the house of Mr. West, touching the point of the conductor on the roof, and appearing again on its base in a thin sheet of flame. Naturally, Franklin was delighted at this first notable result of his grand discovery, and lost no time in examining the traces of the lightning over his conductor. He found that the sharp metal point at the upper end had been melted, and the small brass wire reduced from ten to seven and a half inches, with its top very blunt. The thinnest part of the wire, he saw at once, had disappeared in smoke, while the portion below it, a little thicker, had simply been liquefied, sinking down while in a fluid state, and forming a rough irregular cap, lower on one side than on the other. This was a highly interesting test, showing that the wire on the summit of the conductor must not be made too thin, so as to be liable to be burnt. But still more interesting to Franklin was the investigation of the report, confirmed on all sides, that a sheet of flame had been seen at the base of the conductor, where it was connected with the earth. He at once suspected that the earth at the point, and down to the end of the metal rod, had been very dry, and such indeed was the case. Hence he arrived at the conclusion that all conductors should go deep enough into the earth to find sufficient moisture quickly to dissipate the electric fluid. All subsequent experience, down to the present day, has proved that the inference of the practical philosopher of Philadelphia was as sound in this respect as in the rest of his ever clear and lucid judgments.

Like most other inventions and discoveries, that of the lightning conductor was destined not to be without its early martyrs. Among the many searchers in the science of electricity on the continent of Europe who had eagerly seized the ideas of Benjamin Franklin, and entered enthusiastically upon the experiments recommended by him, was Professor George Wilhelm Richmann, of St. Petersburg. He had conceived some theories of his own regarding electrical discharges, and constructed for experimental purposes an apparatus which he called the ‘gnomon,’ one of the uses of which was to measure the comparative strength of electrical currents. The instrument consisted of a tube of metal, terminating in a small glass vessel, into which, for some unknown reason, he put a quantity of brass filings. Attached to the tube of metal, at its top, was a chain, so arranged as to be easily attached or detached from it, and this was fastened to an iron rod going to the roof, in the form of a lightning conductor, as prescribed by Franklin. It seems to have been the notion of the professor that he might lead the electrical current from the clouds down into his ‘gnomon’ bottle, there to measure its strength; though it is difficult to conceive how a man acquainted with the manifestations of the mystic force with which he was experimenting, and knowing its powerful effects, should not have perceived the extreme danger of thus leading it into a nonconducting element. However, the enthusiastic man, evidently blind to all consequences, set out on his course of experiments. A violent thunderstorm coming over St. Petersburg on August 6, 1753, Professor Richmann hurried to his ‘gnomon,’ attached the chain to the phial, and then stood to watch the effect, with not more than a foot and a half distance between his head and the glass tube. Near him, but further behind, stood a friend, M. Solokow, who was going to make a drawing of the electrical apparatus. All on a sudden, there came a terrible flash of lightning, described as ‘a ball of fire’ by M. Solokow, down from the skies, falling upon the ‘gnomon’ and springing from thence upon Professor Richmann, laid the latter dead on the floor, and his companion senseless.

When the body of the unfortunate professor came to be examined, it was found that the electric current had passed right through him, entering at the forehead, and coming out at the sole of the left foot, both places being distinctly marked by red spots and small perforations, like those of a needle. There were no other marks of injury visible, either inwardly or outwardly, except a number of red and blue spots over the back and shoulders, which grew larger the day after, and seemed to bring with them symptoms of rapid decay. Some of the medical men attending the ‘post mortem’ examination were most desirous to enter into further observations, so as to ascertain, if possible, the actual cause which produced death by a stroke of lightning, but they had no opportunity. When they returned to the professor’s house, the second day after his death, the body was already so far decomposed as to be unrecognisable, and it was with difficulty that the remains of the first martyr of applied electricity could be got into a coffin and carried to their last resting-place.

The appalling death of Professor Richmann produced an enormous commotion, far beyond what might be expected from a similar event, throughout the learned world of Europe. In France especially the occurrence created the deepest impression, mingled with admiration of what was called the ‘glorious death’ of the St. Petersburg professor, and more than one student of electrical science boldly declared his determination to become a martyr in the same noble cause. But reflection, probably, brought better counsel, for, as it happened, there were no more contributions, for the time being, to the roll of martyrs.