6.—To this end, one or more conducting channels of copper depending upon the magnitude and extent of the building should be systematically applied to the walls; these conducting channels should consist either of double copper plates united in series one over the other, as in the method of fixing such Conductors to the masts of Her Majesty’s Ships, the plates being not less than 31⁄2 inches wide, and of 1⁄16th and 1⁄8th of an inch in thickness, or the Conductors may with advantage be constructed of stout copper pipe not less than 3⁄16ths of an inch thick, and 11⁄2 to 2 inches in diameter: in either case the Conductors should be securely fixed to the walls of the building, either by braces, or copper nails, or clamps; they should terminate in solid metal rods above, projecting freely into the air, at a moderate and convenient height above the point to which they are fixed, and below they should terminate in one or two branches leading outward about a foot under the surface of the earth; if possible, they should be connected with a spring of water or other moist ground.
It would be proper in certain dry situations, to lead out in several directions under the ground, old iron or other metallic chains, so as to expose a large extent of metallic contact in the surface of the earth.
7.—All the metals in the roof and other parts of the building of whatever kind, should so far as possible have metallic communication with these Alarm Conductors, and in case of any prominent elevated chimney, it would be desirable to lead a pointed conducting tube along it to the metals of the roof; all of which satisfies the conditions above specified.
8.—Remark 1.—It is now proved beyond all questions, that the electrical discharge never leaves perfect conducting lines of small resistance, in order to pass out upon bad conducting circuits, in which the resistance is very great, that is an established law of nature; hence a stroke of Lightning upon such conducting lines will be confined to the Conductors as constituting a line of discharge of less resistance than any other line of discharge through the building, which can be assigned. The apprehension of “Lateral Discharge” therefore, from the Conductor, is quite absurd; and is not countenanced by any fact whatever; if any doubt could possibly exist, it would be now most completely set at rest by the experience of the permanent Conductors, applied to the masts of Her Majesty’s ships. In very many instances furious discharges of Lightning have fallen on the masts with a crash as if the ship’s broadside had been fired, and the solid point aloft has been found melted; in all these cases electrical discharge robbed by the Conductor of its explosive violence, has traversed the line of action to the sea, through the ship, and through the copper bolts, driven through the ship’s solid timbers, without the least damage to the surrounding masses, whether metallic, as in the case of the massive iron hoops on the lower masts, or not. Persons have either been close by or actually leaning against the Conductors at the time, without experiencing any ill consequence.
9.—Remark 2.—It has also been incontestably shown, that metallic bodies have not any specific attractive force or affinity for the matter of Lightning; metals are as little attractive of lightning as wood or stone. All matter is equally indifferent to Electricity so far as regards a specific attraction, hence the idea that metals attract or invite Lightning is a popular but very unlearned error contradicted by the most satisfactory evidence, and the whole course of experience; in short, we find that Lightning falls indiscriminately upon trees, rocks, and buildings, whether the buildings have metals about them or not.
10.—Remark 3.—A building that is hence clear, may be struck and damaged by Lightning without having a particle of metal in its construction; if there be metals in it, however, and they happen to be in such situations as will enable them to facilitate the progress of the electrical discharge, so far as they go, then the discharge will fall on them in preference to other bodies offering more resistance, but not otherwise; if metallic substances be not present, or if present, they happen to occupy places in which they cannot be of any use in helping on the discharge in the course it wants to go, then the electricity seizes upon other bodies, which lie in that course, or which can help it, however small their power of doing so, and in this attempt such bodies are commonly, but not always, shattered in pieces. The great law of the discharge is,—progress between the terminating planes of action, viz:—the clouds and earth, and in such line or lines as upon the whole, offer the least mechanical impediment or resistance to this operation, just as water falling over the side of a hill in a rain storm, picks out or selects as it were by the force of gravity, all the little furrows or channels which lie convenient to its course, and avoids those which do not. If in the case of Lightning you provide through the instrumentality of efficient Conductors, a free and uninterrupted course for the electrical discharge, then it will follow that course without damage to the general structure; if you do not, then this irresistible agency will find a course for itself through the edifice in some line or lines of least resistance to it, and will shake all imperfect conducting matter in pieces in doing so; moreover it is to be specially remarked in this case, that the damage ensues, not where the metals are, but where they cease to be continued, the more metal in a building therefore the better, more especially when connected by an uninterrupted circuit with any medium of communication with the earth.
Such is, in fact, the great condition to be satisfied in the application of Lightning Conductors, which is virtually nothing more than the perfecting a line or lines of small resistance in given directions, less than the resistance in any other lines in the building, which can be assigned in any other direction, and in which by a law of nature the electrical agency will move in preference to any others.
11.—It follows from the foregoing principles, that a magazine constructed entirely of iron or other metal, would be infinitely more safe in Lightning storms than if built with masonry in the usual way; metallic roofs for magazines, with capacious metallic Conductors to the earth, would be unobjectionable, and a source of security.
Metallic gutters and ridges having continuous metallic connection with the earth are also unobjectionable.
A good method of Conductors for magazines built of masonry, would be such as already described, regard being had to the position of the building, its extent, and most prominent points, also to the nature, state, and condition of the soil, whether it be moist or dry, alluvial calcareous, or of hard rock; we must also consider the extent, disposition, and peculiar position of the metallic bodies entering into the general structure of the building, whether the roof be flat, pointed, or angular in various parts.