Lippincott's Magazine of Popular Literature and Science, Vol. 26, August, 1880

by Various

It is important that the conductor should form an unbroken line throughout its extent, otherwise there is danger that a portion of the charge may be diverted from it. For instance: a large barn struck not long since had a conductor at each of three corners. In order to maintain the uniformity of the four angles of the square hip roof, a rod was run from the main conductor down the fourth angle to the hip, where it terminated in an erect point. A heavy discharge struck the main rod at the cupola, and, descending, divided among the four branches. That on the short branch jumped from its end to the metal sheathing along the angle of the roof, which it followed to the gutter, passing along this to one of the conductors, doing some damage on the way. Had not the charge found a line of metal on which to continue its course from the end of the rod, it would have done greater damage, and most likely have set the building on fire.

Another point of importance is, that the connection of the joints of the rod be perfect, as explosions and fusion occur wherever the surface in contact is less than the size of the rod, unless the latter is much larger than necessary. The hook and the lap joints, if not very carefully made, are liable to this objection. The best connection, no doubt, is that of the screw coupling.

The insulation of the rod from the building is an expense not only without the least advantage, but the contrary. Harris (Thunderstorms, pp. 129, 131) says: "This practice is not only useless, but disadvantageous, and is manifestly inconsistent with the principles on which conductors are applied." Dr. Franklin says: "The rod may be fastened to the wall, chimney, etc. with staples of iron. The lightning will not leave the rod to pass into the wall through these staples. It would rather, if any were in the wall, pass out of it into the rod, to get more readily by that conductor to the earth." The practice may have gained vogue from an observance of the use of glass knobs as insulators of telegraph-wires. Many intelligent people have failed to apprehend the vast difference between the low tension of voltaic electricity and frictional electricity, lightning being in the nature of the latter. The fact that when lightning strikes the telegraph-wire it jumps from the wire to the posts, often tearing in pieces half a dozen in a row, ought to be conclusive in regard to insulating lightning-rods.

The same considerations will also effectually dissipate the fallacy by which the horizontal lightning-rod has duped so many people in certain portions of the West; for if the wire be cut off from the ground-connections (in which condition it accords with the conductor in question) the posts (which answer to the building thus "protected") must suffer still greater damage. So far from being insulated, the rod should be connected with all considerable masses of metal in the building, these having also a good connection with the earth. Frequently during a thunder-shower—sometimes even on the approach of one—all metallic objects will be electrified, and those of considerable size will often yield a spark; and this without the building containing these objects being struck. When struck, the larger masses of metal might occasion a dangerous explosion from induction, though at some distance from the rod: for this reason, as before stated, they should be connected with the ground. Being then liable to receive a part of the current from the conductor in case this be too small, they should be connected with it, as otherwise the current would cause damage in its passage. In a word, therefore, all metal bodies in a building should, as far as possible, be made a part of the system of conduction. This matter is not well understood generally. A dwelling in Boston having been struck by lightning a few years since, a neighbor remarked that "it was fortunate the lightning did not reach the gas-pipe, for it would then have gone all over the house." The fact was, that the bolt did not go more than five feet inside the house before it struck the pipe, and there all damage ended. The idea may be novel to most people, but if the gas-or water-pipes were carried above the roof to the usual height of lightning-rods, they would form a very efficient system of conductors so long as they were connected with the main pipes in the street. Knowing the destructive character of lightning when it passes through air, wood, brick, stone or other non-conductor, people are naturally fearful of allowing the current to run through their houses. But the lion and the lamb are not more different than are the disruptive discharge while passing through a non-conductor and the same current passing through a good conductor.

The system of lightning-conductors in use in the British navy goes through the woodwork of the vessel, the conductors sunk in the side of the masts connecting with the sea through the metal bolts in the hull. After the terrible charge of electricity had fallen on the Chichester, Captain Stewart wrote: "I examined the planks about the bolts, and found all quite fair and water-tight." (These "bolts" formed the lower part of the system of conduction, passing through the bottom of the vessel and connecting with the water.) After twenty-five years' use there had not, as we learn from the British Nautical Magazine for March, 1853, been a solitary instance of serious damage by lightning on ships fitted with these conductors, though many had been struck by heavy discharges. In our own navy the conductors pass from the upper part of the mast over the side of the vessel.

It is not, however, to advocate making the gas-and water-pipes the main lines of conduction that I have made these citations, but to remove in some degree the dread of "having the lightning come into the house." A better conductor would be the metal covering of the roof when such material is used. When a good metallic connection is made between a metal roof and metal rain-conductors, which, in their turn, are well connected with the earth, nothing further is needed for complete protection than a rod soldered to the roof for each chimney or other projection. But as the lightning is liable to melt the plate at the point where it enters, especially if the metal be tin or zinc, it is well to solder points at the angles. Some, "to make assurance doubly sure," carry the rods over the whole distance quite to the ground in addition. All authorities consider such a system as this to be as complete a defence against lightning as possible.

"If," says Harris, "a building or a ship were perfectly metallic in all its parts, no damage could possibly arise to it when struck by lightning, since the explosive action would vanish the instant the electrical agency entered the metal. In applying lightning-conductors, therefore, as a means of guarding against the destructive effects of lightning, our object should be to carry out this principle in all its generality, and bring the building or ship as nearly as possible into that state of passive electrical resistance it would have supposing the whole mass were iron throughout."

After the most careful and extended inquiry possible to him, it is the writer's conclusion that in nearly every case of serious damage by lightning to a building having conductors of any well-known system (except the horizontal, which is not a conductor at all in the usual sense of the word), the failure to protect has been on account of a defective ground-connection. The fact is the more surprising as this connection is so much within control and is the least costly part of the system. This fault has arisen from the failure of lightning-rod men, as well as owners of buildings, to apprehend what constitutes a ground-connection for electricity. If the eye sees the end of the conductor pass a short distance beneath the surface, all the connection necessary is thought to be effected, because "the ground is always wet enough in a shower." In the cities it is customary to connect the rod with the water-or gas-pipes in the street, which makes the conduction perfect. In the absence of these it is best to carry the rod to a well; and it is always desirable to enlarge the lower end of the conductor, which may be done by soldering it there to a sheet of copper. If the termination of the line cannot be carried to a well, it should be deeply buried in a bed of coke or charcoal that has been subjected to a red heat.

A season or two ago a large barn in the vicinity of Boston was struck by lightning, and though there were rods at three of the four corners, three kine were killed by the discharge. The barn stood upon the side of a hill, having a cellar and sub-cellar, the bottom of the last being very moist. An ox stood in one corner, a cow in another and a heifer at a third, and each received a fatal stroke. On examination it was found that the rods entered the ground to the depth of only about one foot, and the soil, being dry, perfectly insulated them. Consequently, on the way to damp earth the currents jumped to the nearest conductors, which happened to be these unfortunate animals. In placing conductors it must not be forgotten that dry earth in general is not a conductor. Neither will any small quantity of surface water serve to check the rage of the electric stroke, unless there is a connection of moisture with the mass of moisture below the soil.

The depth to which lightning may penetrate before it is so dissipated as to lose its dangerous character is shown by the fulgurites, or "lightning-tubes," sometimes found in sandy soils. Their formation has been conclusively traced to disruptive electrical discharges from the clouds, which have melted the sand by the intense heat generated in passing through to a moist earth. These tubes generally divide into prongs, like a parsnip, as they descend. The inner surface is smooth and very bright. It scratches glass and strikes fire as a flint. They are sometimes found three inches in external diameter, and extending to a depth of thirty feet. In one instance five of these tubes were found in a single hill.