Gerald Molloy

“ Thus, for example, in the open country, if you stand a short distance from a wood, you may consider yourself as practically protected by a lightning conductor. For a wood, by its numerous branches and leaves, favors very much a quiet discharge of electricity, thus tending to suppress altogether the flash of lightning; and if the flash of lightning does come, it is much more likely to strike the wood than to strike you, because the wood is a far more prominent body, and offers, on the whole, an easier path to earth. ”

“ To understand why the sound of thunder reaches the ear as a prolonged peal, we have only to remember that sound takes time to travel. Since a flash of lightning is practically instantaneous, we may assume that the sound is produced at the same moment all along the line of discharge. But the sound waves, setting out at the same moment from all points along the line of discharge, must reach the ear in successive instants of time, arriving first from that point which is nearest to the observer, and last from that point which is most distant. ”

“ Further, the spark from an electric machine travels through space with extraordinary rapidity, and so does a flash of lightning; the spark follows a zig-zag course, and so does a flash of lightning; the spark moves silently and harmlessly through metal rods and stout wires, while it forces its way, with destructive effect, through bad conductors, and it is so, too, with a flash of lightning. Lastly, the electricity of a machine is capable of giving a severe shock to the human body; and we know that lightning gives a shock so severe as usually to cause immediate death. ”

“ But we know, in point of fact, that it lasts for less than the millionth of a second, that is, less than the hundred-thousandth part of the tenth of a second. Therefore we see only the hundred-thousandth part of its real brightness.
Here is a startling conclusion, and one, I may say, fully justified by scientific evidence. That electric spark, brilliant as it appears to us, is really a hundred thousand times as bright as it seems to be. We cannot speak with the same precision of a flash of lightning; because its duration has not yet been so exactly determined. ”

“ The reason why a metal covering affords complete protection is that, when a conductor is electrified, the whole charge of electricity exists on the outside surface of the conductor; and therefore, when a discharge takes place, it is only the outside surface that is affected. Thus, if you were completely incased in a metal covering, and then charged with electricity by the inductive action of a thundercloud, it is only the metal covering that would undergo any change of electrical condition; and when the lightning flash would pass, it is only the metal covering that would be discharged. ”

“ The Outer Shell only of a Lightning Rod Acts as a Conductor.—As a consequence of self-induction or electrical inertia, Professor Lodge contends that a lightning discharge in a conductor consists of a series of oscillations. These oscillations follow one another with extraordinary rapidity—there may be a hundred thousand in a second, there may be a million. Now it has been shown that, when a current starts in a conductor, it does not start at once all through its section; it begins on the outside, and then gradually, but rapidly, penetrates to the interior. ”

“ Physical Cause of Thunder.—Let us now proceed to consider the phenomenon of thunder, which is so intimately associated with lightning, and which, though perfectly harmless in itself, and though never heard until the real danger is past, often excites more terror in the mind than the lightning flash itself. The sound of thunder, like that of the electric spark, is due to a disturbance caused in the air by the electric discharge. ”

“ First, if we accept the results arrived at by Professor Ogden Rood, of Columbia College, what appears to the eye as a single flash of lightning, consists, in fact, as a general rule, of a succession of flashes, each one of which must naturally produce its own peal of thunder; and although the several flashes, if they follow one another at intervals of the tenth of a second, will make one continuous impression on the eye, the several peals of thunder, under the same conditions, will impress the ear as so many distinct peals. ”

“ If an electrical engineer finds a resistance of a hundred ohms, he will rightly pronounce the earth contact to be very bad indeed. But why should the lightning flash leave a conductor with a resistance of a hundred ohms in order to follow a line of non-conductors where it encounters a resistance of many thousand ohms? ”

“ When lightning strikes a building, it is very apt to use the stack of chimneys in making its way to earth, partly because the stack of chimneys is generally the most prominent part of the building, and partly because, on account of the heated air and the soot within the chimney, it is usually a moderately good conductor. Therefore, if you be indoors, you must keep well away from the chimneys; and for a similar reason, you must keep as far as you can from large masses of metal of every kind. ”

“ The effects of lightning, on the bodies that it strikes, are analogous to those which may be produced by the discharge of our electric machines and Leyden jar batteries. When the discharge of a battery traverses a metal conductor of sufficient dimensions to allow it an easy passage, it makes its way along silently and harmlessly. But if the conductor be so thin as to offer considerable resistance, then the conductor itself is raised to intense heat, and may be melted, or even converted into vapor, by the discharge. ”

“ I would observe, however, that the lightning conductor ought not to be connected directly with the soft leaden pipes which are commonly employed to convey gas and water to the several parts of a building. Such pipes, as we have seen, are liable to be melted when any considerable part of the lightning discharge passes through them; and thus much harm might be done, and the building might even be set on fire by the lighting of the gas. Every good end will be attained if the conductor is put in metallic connection with the iron gas and water mains either inside or outside the building. ”

“ But every one must have observed that even an individual peal of thunder often undergoes similar changes, swelling out at one moment with great power, and the next moment rapidly dying away. To account for this phenomenon, I would observe, first, that there is no reason to suppose that the disturbance caused by lightning is of exactly the same magnitude at every point of its path. On the contrary, it would seem very probable that the amount of this disturbance is, in some way, dependent on the resistance which the discharge encounters. ”

“ But whatever these sources may be, there can be little doubt that the electricity of the atmosphere is intimately associated with the minute particles of water vapor of which the thundercloud is eventually built up. This consideration is of great importance when we come to consider the special properties of lightning, as compared with other forms of electricity. The most striking characteristic of lightning is the wonderful power it possesses of forcing its way through the resisting medium of the air. ”

“ Precaution Against Rival Conductors.—But it is not enough to provide a good lightning conductor, which is itself able to convey the electric discharge harmless to the earth; we must take care that there are no rival conductors near at hand in the building, to draw off the lightning from the path prepared for it, and conduct it by another route in which its course might be marked with destruction. This precaution is of especial importance at the present day, owing to the great extent to which metal, of various kinds, is employed in the construction and fittings of modern buildings. ”

“ Thus we have two bodies—the cloud and the earth—charged with opposite kinds of electricity, and separated by a stratum of the atmosphere. The two opposite electricities powerfully attract each other; but for a time they are prevented from rushing together by the intervening stratum of air, which is a non-conductor of electricity, and acts as a barrier between them. ”

“ The building to be protected is itself in electrical communication with the earth, and the lightning conductor, if efficient, is also in electrical communication with the earth—therefore, the lightning conductor and the building are in electrical communication with each other through the earth, and any attempt at insulating them from one another above the earth is only labor thrown away. ”

“ As a general rule, in fine, clear weather, the electricity of the atmosphere is positive, and not very strongly developed. In wet weather the charge may be either positive or negative, and is generally strong, especially when there are sudden heavy showers. In fog it is also strong, and almost always positive. In a snowstorm it is very strong, and most frequently positive. Finally, in a thunderstorm it is extremely strong, and generally negative; but it is subject to a sudden change of sign, when a flash of lightning passes or when rain begins to fall. ”

“ I had, moreover, beside me a portion of a chain cable through which a lightning discharge had passed, the electricity in passing from link to link encountering a resistance sufficient to enable it to partially fuse the chain. The abolition of resistance is absolutely necessary in connecting a lightning conductor with the earth, and this is done by closely embedding in the earth a plate of good conducting material and of large area. The largeness of area makes atonement for the imperfect conductivity of earth. ”

“ What a Flash of Lightning is.—Lightning, then, may be conceived as an electrical discharge, sudden and violent in its character, which takes place, through the atmosphere, between two bodies highly charged with opposite kinds of electricity. ”

“ Cases are not uncommon in which builders provide underground a carefully constructed reservoir of water, into which the lower end of the lightning rod is introduced. The idea seems to prevail that a reservoir of water constitutes a good earth contact; and this is quite true of a natural reservoir, such as a lake, where the water is in contact with moist earth over a considerable area. But an artificial reservoir may have quite an opposite character, and practically insulate the lightning conductor from the earth. ”

“ While the old guard was being turned out to receive the new, a blinding flash of lightning was seen, accompanied instantly by a terrific peal of thunder. The whole of the old guard, together with part of the new, were thrown violently to the earth. The shock was so severe and sudden that, in most cases, the rear rank men were thrown across the front rank men. One [Pg 35] man was instantly killed, and thirty-two men were more or less severely burned by the electric fluid. ”

“ 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. ”

“ Heat is generated by the expenditure of electrical energy, in overcoming the resistance offered by the atmosphere; and this heat is so intense, that it produces a brilliant incandescence along the path of [Pg 10] the discharge. When a spark appears, for example, between the conductor of the machine and this brass ball, it can be shown, by very satisfactory evidence, that minute particles of these solid bodies are first converted into vapor, and then made to glow with intense heat. ”

“ In a large town the best earth connection is furnished by the system of water-mains and gas-mains, each of which constitutes a great network of conductors everywhere in contact with [Pg 42] the earth. Two points, however, must be carefully attended to—first, that the electrical contact between the lightning conductor and the metal pipe should be absolutely perfect; and, secondly, that the pipe selected should be of such large dimensions as to allow the lightning an easy passage through it to the principal main. ”

“ Mischief Done by Bad Conductors.—If the earth contact is bad, a lightning conductor does more harm than good. It invites the lightning down upon the building without providing for it, at the same time, a free passage to earth. The consequence is that the lightning forces a way for itself, violently bursting asunder whatever opposes its progress, and setting fire to whatever is combustible. ”