Fig. 1. Fig. 2.
Some of the simplest and most practical galvanometers, specially designed for ascertaining the actual efficiency of conductors, have been made in recent years in Germany. The author of this work had constructed for him by Mr. H. Yeates, of Covent Garden, the one, with some improvements, as shown in the subjoined engravings: the first, [fig. 1], exhibiting the arrangement of the battery and resistance coils, and the second, [fig. 2], giving a diagram of the battery current. The battery consists of three cells, and is a modification of the old manganese cell, in which the carbon and oxide of manganese occupy the outer, and the zinc plate the inner, or porous, cell. By this arrangement, the surface of the negative element is greatly increased, and hence a more constant current is obtained, on account of the battery not polarising so rapidly as in the old form. Another advantage of this arrangement is, that the cells can be almost entirely sealed up, the air-openings being made within the porous cell. In the centre of the lid of the box is placed the galvanometer with a ‘tangent’ scale; and on the left are two terminals, by the connection of which the conductor can be examined. On the right hand end of the lid are placed five keys, marked respectively, L, B, 1, 2, 3. Under B is one pole of the battery, so that by depressing this key, as will be seen by the connections in the diagram ([fig. 2]), the battery current is sent through the galvanometer direct. If, however, key No. 1 is depressed, the battery is connected with the galvanometer through a known resistance—key No. 2 has a larger resistance, and No. 3. still larger. The fifth key, L, closes the circuit within the limit of the instrument, but on being depressed opens it, and includes the line or conductor placed between the two terminals at the other end, the battery key at the same time being pressed down. By this arrangement it will be seen that the resistance of the line or conductor may be compared with the known resistance connected with any of the keys Nos. 1, 2, 3, or any of these resistances may be included with that of the line, so as to get a convenient deflection of the galvanometer needle. In the case, with the battery, is a bobbin of insulated wire for connecting the instrument with the conductor and earth which is to be tested. The whole arrangement here described and illustrated is exceedingly portable, being in the form of a small carpet bag, and therefore particularly fitted for persons inspecting lightning conductors and making periodical tests, without which it cannot be too widely known there is really no trustworthy security of protection in lightning conductors.
CHAPTER VI.
CHARACTER OF LIGHTNING AND OF THUNDERSTORMS.
It is well remarked by Arago, that although we know nothing about lightning, beyond the well-ascertained fact that it is one of the manifestations of the equally vast and mysterious electric forces pervading the universe, we yet may ascertain a great deal about its mode of action by continued observation, made by many persons and at many places. As yet the wise recommendation of the French astronomer has, unfortunately, not been acted upon to any extent, or in any systematic manner; still, a good many facts and incidents have been gathered which serve to throw a strong light upon the apparently erratic, but in reality normal manner in which, as in obedience to some grand unfathomable cosmic law, the fire of the clouds flashes along its self-made path. That these observations are entirely modern, detracts nothing from their value. With all their famed civilisation, the classical nations of the ancient world never came to look upon lightning and thunderstorms as regular functions of nature, but regarded them with dread and horror. Even the greatest of their natural philosophers found in them means only for encouraging popular superstition. Thus Pliny the Elder, in his celebrated ‘Natural History,’ recommends, like Arago, notes being taken about thunderstorms, but for quite a different purpose. ‘Nothing is more important,’ says the celebrated author of the Historia Naturalis, than to observe from what region the lightnings proceed, and towards what region they return. Their return to the eastern quarter is a happy augury. When they come from the east, the prime quarter of the Heavens, and likewise return thither, it is the presage of supreme felicity.’ It is reported by travellers that this form of superstition—which has reference, of course, to the zigzag form of many strokes of lightning, apparently in turn advancing and retrograding—still exists in some districts of Southern Italy.
The superstitious awe with which lightning was looked upon not only in ancient times, but in which it is still held by the ignorant at the present day, finds its easy explanation both in the nature of the terrifying phenomenon, and in the fact that even now we can only speculate upon some of the causes of its seemingly capricious actions. There can be no doubt that thunderstorms will visit some districts in preference to others, and that lightning will descend constantly upon some selected spots, and will entirely keep away from others. As regards the latter case, old historians were fond of quoting the grand temple of Solomon at Jerusalem, which was never struck by lightning in the course of a thousand years, although thunderstorms burst unceasingly over the Holy City, creating immense havoc and destruction. In this instance at least, the explanation is simple, although it may not be so in many others. It is stated expressly in the biblical description of the building of the world-famed temple (1 Kings vi. 21, 22) that ‘Solomon overlaid the house within with pure gold; and he made a partition by the chains of gold before the oracle; and he overlaid it with gold. And the whole house he overlaid with gold, until he had finished all the house; also the whole altar that was by the oracle he overlaid with gold.’ If wise King Solomon had known Franklin’s discovery of the protection against lightning given by metallic conductors, he could not have guarded his magnificent edifice better than he did by having ‘the whole house overlaid with gold,’ as stated in the Bible. But he did even more than this, according to the historian Josephus, who records that the roof of the Temple, constructed in what is now called the Italian style, was ornamented from end to end with sharply pointed and thickly gilded pieces of iron, in lancet form. These points, the historian surmised, were placed there to prevent the birds from settling on the magnificent roof, and soiling it, and it is very possible that this was the original design. Nevertheless, it is certain that King Solomon guarded, although, probably, without intending to do so, his magnificent temple as perfectly against lightning, as could have been accomplished by the best arranged system of conductors. It is not often that many thousands of pounds are spent for protection against lightning, even if intended for great cathedrals and splendid royal palaces; but King Solomon disbursed, by the most trustworthy calculations, no less than thirty-eight millions sterling in covering the temple with one of the best of conductors—including the pointed and gilded lancets along the roof, as perfect ‘Franklin rods’ as were ever designed by any architect.
If it is easy to account for the old historical marvel of Solomon’s temple having stood unharmed amidst the ragings of lightning from tens of thousands of storms, it is more difficult to find the reason why many buildings of another kind should be constantly under attack. A notable case in point, related by the German naturalist G. Ch. Lichtenberg, occurred at the village of Rosenberg, in the province of Carinthia, Austria, belonging to the noble family of Orsini. The village church, although not standing in a very elevated position, was unceasingly struck, in the course of the seventeenth and eighteenth centuries, by lightning, which sometimes battered in the roof, sometimes broke down part of the steeple, and often flew in at the window on one side and out on the other. Very possibly, there were large pieces of metal on the wall, or in the roof; or, if not, there may have been masses of water near, underground, sufficient to account for the manifestations of the electric force. However, popular opinion, utterly ignorant as to such causes, ascribed the whole to the doings of evil spirits, and endless attempts were made to exorcise them by prayers, fastings, and sprinkling of holy water. But it was all unavailing. The lightning came again and again, and in the summer of 1730, a flash from the clouds, more violent than any preceding one, demolished the entire steeple. The Orsini family, suspected by many of the lower people of being the secret originators of all the mischief, in league with the evil spirits, erected another steeple, handsomer and far more solid than the one destroyed, to show their pious intentions. But the lightning visited it as before, on the average five or six times a year, doing so much damage that the whole church had to be taken down in 1778, being found in ruins. Happily, in the meanwhile the report had gone as far as the little village in Carinthia that something had been discovered for guarding all buildings, including spirit-haunted churches, against damage by lightning. Once more, the proprietors of the village built a new church on the old ground, but this time, by the advice of an Italian architect, they placed upon it one of the ‘heretical rods,’ made famous for having done good service in protecting the cathedral of Siena. Needless to say that it did again similar service.
It is very probable that, besides the two causes just referred to which divert the path of lightning, there are many others of influence, at present entirely unknown. Numerous cases are reported where the electric discharge from the clouds touched precisely, and with singular accuracy, as if directed by a superior intelligence, the same spot, without the slightest reason being discoverable for such an action, after the most minute investigation by competent persons. Thus, on June 29, 1763, a violent thunderstorm broke over the village of Antrasme, near Laval, in France, the residence of a distinguished investigator of electrical phenomena, Count de Labour-Landry, a friend and correspondent of the Abbé Nollet as well as of Benjamin Franklin. The lightning struck, as carefully ascertained by the Count, first the steeple of the church, then sprang to one of the lower walls, where it fused and blackened the gilding of picture frames and some other metallic ornaments, melting also some pewter flasks used for sacramental purposes, and finally opened two deep holes, as regular as if they had been drilled with an auger, in a wooden table, placed within a recess of soft stone. All these damages were duly repaired; but, to the boundless surprise of the witnesses, the lightning struck the church almost exactly a year after, on June 20, 1764, entering the church by the same way as before, fusing and blackening the same gildings, melting the same flasks, and, in the end, driving out the very plugs of the wooden table inserted to fill the holes bored by the previous stroke of lightning. The account of the whole might seem almost incredible, were it not attested by independent eye-witnesses. Arago, with absolute faith in their testimony, remarks thereon that ‘those who will take the trouble of reflecting upon the thousands of combinations which might have caused the path of the lightning to have been different in the two cases, will, I imagine, have no hesitation in viewing, with me, the perfect identity of effect as demonstrating the truth of a proposition I put forward,’ namely, that ‘lightning, in its rapid march, is influenced by causes, or actions, dependent on the terrestrial bodies near which it explodes.’ In other words, lightning, like many other phenomena of earth, air, and water, is influenced by unknown causes. Hamlet says very much the same, when exclaiming: