Lightning Conductors: Their History, Nature, and Mode of Application

by F.C.S. Richard Anderson

There are more things in heaven and earth, Horatio,
Than are dreamt of in your philosophy.

After all possible explanations, Arago could get no further than Horatio, who thought that there was much in the universe which was ‘wondrous strange.’

It does not seem impossible that some of the extraordinary effects of lightning, either in striking repeatedly certain objects, or in seldom or never touching others, may be explained on meteorological grounds. The height, as well as thickness, of the clouds charged with the electric fire, must naturally greatly influence the direction of the latter, and though both elements vary enormously, in different countries and at different seasons, it is likely enough that the variation is comparatively trifling under given conditions, as, for example, in a district where there are prevailing winds, and where the configuration of the earth powerfully acts upon the drift and movement of the aerial masses, and the atmospheric conditions in general. As to the height of the clouds charged with lightning, there appears scarcely any limit, as it has been found that they at times rise above the summit of the most elevated mountain ridges on the face of the globe. The great naturalist and traveller, Alexander von Humboldt, measured the height of a storm cloud, discharging lightning, near the mountain of Toluca, in Mexico, and found that it was no less than 4,620 metres, or 15,153 English feet, above the level of the sea. The height of another, ascertained by Professor de Saussure, of Geneva, when ascending Mont Blanc, was 4,810 metres, or 15,776 English feet, or almost exactly three miles. Probably, these are exceptional cases, as even in mountainous districts the heavy moist and electricity-laden clouds seldom rise to such extraordinary heights; still, even such as they are they do not represent the extreme limit of elevation. A member of the French Academy of Sciences, M. De Lisle, records having measured, by trigonometrical observations, the vertical height of clouds in a thunderstorm, with strong flashes of lightning, which broke over Paris, and found it to be 8,080 metres, or 26,502 English feet. Consequently, this cloud-mass, charged with electricity, stood far above the summit of the highest mountain peak in the world.

If some of the lightning-clouds tower at a gigantic elevation over the earth’s surface, there are others that lie almost flat on it. There are some remarkable observations on this kind in existence, made by German meteorologists. Two of these deserve particular notice. On August 27, a heavy storm burst over the town of Admont, on the river Ens, in Styria, and the lightning, falling upon the lower part of the great convent of the Benedictines, and passing through the wall, killed two young priests near the altar, while reading vespers. The convent lies, like the town of Admont, in a valley, and above it, some three hundred feet higher, stands a castle, in which resided at the time a German professor, specially interested in the phenomena of thunderstorms. He watched assiduously the coming storm, and saw the lightning fall upon the great convent, noticing all the while that the gilded cross placed on the belfry of the edifice, about 115 feet from the ground, remained standing out clear above the electric cloud, which appeared to come close to the earth’s surface. He noticed further that above this cloud, enveloping the ground portion of the Benedictine convent, there hovered another, more than two thousand feet higher, and at intervals he could see streaks of lightning fly from between the two, not however from the more elevated to the lower one, but in a contrary direction. It was evident that the two clouds must have been charged by electric forces of different ‘degree,’ or ‘potential;’ it may be, one of a ‘negative’ and the other of a ‘positive’ kind, or, as Benjamin Franklin termed them, ‘plus’ and ‘minus;’ although, as long as the forces differ in ‘degree’ or ‘potential,’ it is not essential that they be of opposite kinds. As the marvellously sagacious discoverer of the lightning conductor surmised, the wondrous force is really unitarian—that is, throughout the same, the term ‘kind’ really only indicating on which side of an assumed zero (the potential of the earth) the observations or measurements are made.

Another notable instance of low-lying storm-clouds, and which furnished the rare opportunity of measuring the thickness of one of them, occurred at the city of Gratz, Austria, on June 15, 1826. The city is built along the side of a hill, the highest point of which, called the Schlossberg, has on its summit a castle, now in ruins, but at the time garrisoned by troops, and furnished with a small observatory. When the storm in question broke over the city, several scientific men on the Schlossberg took notes of the movement and direction of the great cloud emitting its electric discharges. This they could easily do, as they themselves, on their altitude, were standing in sunshine, under a perfectly blue sky, the dark cloud-wave rolling deep under their feet, indicating its path and size by streams of fire, following each other in rapid succession. Exclusive of short flashes, vanishing in the air as soon as seen, there fell nine great strokes of lightning upon buildings in the city, in the course of about three quarters of an hour, five of them causing conflagrations and killing a number of people. The storm over, the observers compared their measurements, and it was then found that the height of the storm cloud had never been above the clock-tower of the Johanneum, an edifice connected with the university, and containing a library and museum, while the lowest part of it had gone down the sloping ground of the city no further than 120 feet under the summit of the clock-tower. This, then, was the exact thickness of the storm-cloud which had caused so much destruction. It was noticed on this occasion, as had been done often before, that the discharges of lightning fell all upon buildings standing on moist ground, near the river Mur, a mountain stream coming from the Noric Alps, and dividing the city into two parts. There can be no doubt, from thousands of observations made, that it is one of the characteristics of the electric force to seek its way towards water—to be, as it were, dissolved by it, or, as perhaps it might be said more truly, to be equalised by it. A very remarkable electrical phenomenon, and one which is often attended with fatal results to men and animals, is what is known as the ‘return stroke’ of a lightning discharge. This is always less violent than the direct stroke, but is nevertheless very powerful. It is caused by the inductive action which a thunder-cloud exerts on bodies placed within the sphere of its activity, and disastrous effects often take place upon objects, upon men and animals on the earth under the cloud, although perhaps miles away from the point where the discharge takes place. These bodies are, like the ground, charged with the opposite electricity to that of the cloud; but when the latter is discharged by the recombination of its electricity with that of the ground, the induction ceases, and all the bodies charged by induction return to a neutral condition. The suddenness of this return constitutes the dangerous ‘return stroke.’

Lord Mahon was the first to demonstrate by experiment its mode of action; as shown in the following illustration.

A B C is the electrified cloud, the two ends of which come near the earth. The lightning discharge occurs at C. A man at F is killed by the return stroke, while those at D, nearer to the place of discharge, but further from the cloud, receive no injury. It may be mentioned that it was the action of the return shock upon the limbs of a dead frog in Galvani’s laboratory that led to the Professor’s experiments on animal electricity, and further to the discovery by Volta of that form of electrical action which bears his name.

The subject of the origin of atmospheric electricity has at all times been a favourite source of speculation with scientific investigators, and given rise to numerous hypotheses. The eminent Swiss savant, Professor de Saussure, already referred to, held that all atmospheric electricity was due to the evaporation of the waters of the globe through the effect of the sun. To prove this, he made a great number of experiments, showing that whenever water, whether pure or containing more or less salt, whether acid or alkaline, is projected upon a metal crucible heated to redness, the evaporation that takes place immediately is accompanied by strong liberation of electricity. The fact is undisputed by scientific men, but not so the conclusion. Another eminent savant, no less distinguished than De Saussure, Professor De la Rive, in taking up the experiments of the former, succeeded in showing that the production of atmospheric electricity by throwing water upon heated metal was not the simple effect of evaporation, but due to chemical causes.

Of the numberless attempts made to elucidate the phenomena of electricity, in connection with the formation of thunderstorms, none seem more worthy of regard, and of thoughtful consideration, than those of Jean Athanase Peltier, a French savant, little known to the general world. Born in 1785, he occupied his whole life, until his death in 1845, with the study of meteorology and electricity, making, among others, the important discovery that a current flowing through a circuit composed of two metals joined together heats or cools the junction according to the direction of the current. From all the experiments upon the phenomena of electricity, to which he devoted his life, Peltier drew the conclusion that the earth itself, and more particularly the fiery liquid mass forming the inner bulk of it, over which the solid crust and the ocean lie, but both thinner in comparison than the skin of an apple, form one immense reservoir of electricity. As light comes from the sun, generated, as we believe, by heat, so the electric force, he held, comes from the interior of the globe, likewise generated by heat. The atmosphere surrounding the globe, Peltier asserted, produced no electricity whatever, nor held it, except temporarily. But he thought it possible that it might exist, engendered by other flaming masses than those of the earth’s interior, in the interminable planetary spaces, which no astronomer can measure, and of which imagination itself, in its loftiest flights, can form no more conception than the finite ever can of the infinite. On the whole, Peltier’s explanation, such as it is, may fairly be accepted, in the present state of the scientific investigation, as one of the best that can be given. For the rest, men must content themselves to study the phenomena of electricity, and to regard it simply as one of the great, if mysterious, forces of nature.