Introduction of Lightning Rods into England.—The progress of lightning conductors was more slow in England and on the Continent of Europe, owing to a fear, not unnatural, that they might, in some cases, draw down the lightning where it would not otherwise have fallen. People preferred to take their chance of escaping as they had escaped before, rather than invite, as it were, the lightning to descend on their houses, in the hope that an iron rod would convey it harmless to the earth. But the immense amount of damage done every year by lightning, soon led practical men to entertain a proposal which offered complete immunity from all danger on such easy terms; and when it was found that buildings protected by lightning conductors were, over and over again, struck by lightning without suffering any harm, a general conviction of their utility was gradually established in the public mind.
The first public building protected by a lightning rod in England was St. Paul’s Cathedral, in London. On the eighteenth of June, 1764, the beautiful steeple of Saint Bride’s Church, in the city, was struck by lightning and reduced to ruin. This incident awakened the attention of the dean and chapter of St. Paul’s to the danger of a similar calamity, which seemed, as it were, impending over their own church. After long deliberation, they referred the matter to the Royal Society, asking for advice and instruction. A committee of scientific men was appointed by the Royal Society to consider the question. Benjamin Franklin himself, who happened to be in London at the time, as the representative of the American States in their dispute with England, was nominated a member of the committee. And the result of its deliberation was that, in the year 1769, a number of lightning conductors were erected on St. Paul’s Cathedral.
It was on this occasion that arose the celebrated controversy about the respective merits of points and balls. Franklin had recommended a pointed conductor; but some members of the committee were of opinion that the conductor should end in a ball and not in a point. The decision of the committee was in favor of Franklin’s opinion, and pointed conductors were accordingly adopted for St. Paul’s Cathedral. But the controversy did not end here. The time was one of great political excitement, and party spirit infused itself even into the peaceful discussions of science. The weight of scientific opinion was on the side of Franklin; but it was hinted, on the other side, that the pointed conductors were tainted with republicanism, and pregnant with danger to the empire. As a rule, the whigs were strongly in favor of points; while the Tories were enthusiastic in their support of balls.
For a time the Tories seemed to prevail. The king was on their side. Experiments on a grand scale were conducted in his presence, at the Pantheon, a large building in Oxford street; he was assured that these experiments proved the great superiority of balls over points; and to give practical effect to his convictions, his majesty directed that a large cannon ball should be fixed on the end of the lightning conductor attached to the royal palace at Kew. But the committee of the Royal Society remained unconvinced. In course of time the heat of party spirit abated; experience as well as reason was found to be in favor of Franklin’s views; and the battle of the balls and points has long since passed into the domain of history.[27]
Functions of a Lightning Conductor.—A lightning conductor fulfills two functions. First, it favors a silent and gradual discharge of electricity between the cloud and the earth, and thus tends to prevent that accumulation which must of necessity take place before a flash of lightning will pass. Secondly, if a flash of lightning come, the lightning conductor offers it a safe channel through which it may pass harmless to the earth.
These two functions of a lightning conductor may be easily illustrated by experiment. When our machine is in action, if I present my closed hand to the large brass conductor, a spark passes between them, and I feel, at the same moment, a slight electric shock. Here the conductor of the machine, as usual, holds the place of the electrified cloud; my closed hand represents, as it were, a lofty building that stands out prominently on the surface of the earth; the spark is the flash of lightning, and the electric shock just suggests the destructive power of the sudden disruptive discharge.
Now let me protect this building by a lightning conductor. For this purpose, I take in my hand a brass rod, which I connect with the earth by a brass chain. In the first instance, I will have a metal ball on the end of my lightning conductor. You see the effect; sparks pass rapidly, but I feel no shock. I can increase the strength of the discharge by hanging this condensing jar on the conductor of the machine. Sparks pass now, much more brilliant and powerful than before, but still I get no shock. It is evident, therefore, that my lightning rod does not prevent the flash from passing, but it conveys it harmless to the ground.
I next take a rod which is sharply pointed, and connecting it as before with the earth by a brass chain, I present the sharp point to the conductor of the machine. Observe how different is the result; there is no disruptive discharge; no spark passes; no shock is felt. Electricity still continues to be generated in the machine, and electricity is generated, by induction, in the brass rod, and in my body. But these two opposite electricities discharge themselves silently, by means of this pointed rod, and no sensible effect of any kind is exhibited.
These experiments are very simple, but they really put before us, in the clearest possible way, the whole theory of lightning conductors. In particular, they give us ocular demonstration that an efficient lightning rod not only makes the lightning harmless when it comes, but tends very much to prevent its coming. A remarkable example, on a large scale, of this important property, is furnished by the town of Pietermaritzburg, the capital of the colony of Natal, in South Africa. This town is subject to the frequent visitation of thunderstorms, at certain seasons of the year, and much damage was formerly done by lightning, but since the erection of lightning conductors on the principal buildings, the lightning has never fallen within the town. Thunderclouds come as before, but they pass silently over the city, and only begin to emit their lightning flashes when they reach the open country, and have passed beyond the range of the lightning conductors.[28]
But it will often happen, even in the case of a pointed conductor, that the accumulation of electricity goes on so fast that the silent discharge is insufficient to keep it in check. A disruptive discharge will then take place, from time to time, and a flash of lightning will pass. Under these circumstances, the lightning conductor is called upon to fulfill its second function, and to convey the lightning harmless to the earth.