Publication: Scientific American
New York, NY, United States
More about Lightning Rods.
The subject of lightning rods is one of great interest to every man and woman in our land, and from the many fatal accidents which have taken place this season during thunder storms, it is exciting much attention at present; of this we are certain, from the number of letters we have recently received on the subject. - There is no saying more common than "doctors certainly differ," and it is just as applicable to the different opinions entertained by different men, respecting lightning rods, as anything else. One considers that a round form of lightning rod, is as good as any other; a second considers a square form the best, while a third looks upon the twisted form as the best of all. One advocates glass insulators for the rods, while another asserts that wooden brackets are sufficient. One advocates a continuous rod like a wire, while another believes the chain or the jointed conductor to be perfectly safe. One says the conducting surface is the grand desideratum, while another says "the solid section is the main object." Out of these conflicting views can anything certain and tangible be adduced for the construction and erection of safe lightning rods? We believe there can. The requisites of a good lightning conductor are well known, and the different opinions advanced respecting this and that conductor, refer more to the most effectual conductor which can be made at the smallest cost than to the real scientific merits of a lightning conductor in itself, as it relates to perfect action. A thick iron or copper rod extending above the highest part of a house, continuous in its connection, perfectly insulated, kept separate and distant from any large metallic body, and terminating in a moist part of the earth, such as a pool or well, is a perfect lightning conductor. While we write this, we have before us a model of the lightning conductor of G. W. Otis, of Lynn, Mass., for which a patent was granted on the 26th August, 1851, and which now owned by L. Lyon & Co., of this city, (Mr. Lyon is the author of a treatise on lightning conductors recently published by Putnam) it is a good and certain conductor, but expensive. There are some, however, to whom expense is but a secondary consideration, and for their benefit we will describe it. The main rod is of iron, square in form, and made in sections screwed into one another, in metal eyes, secured to the binding insulators, which are glass cylinders secured to dry wooden collars that bind them to the building. Each binder terminates in a horizontal point at its extremity; the upper parts of the conductor are composed of many points branching off, and all tipped with gold. The insulation is perfect, and the rod is more nearly continuous than if it were formed in link sections. The use of any non-conducting substance as an insulator is old and well known, and any person who wishes to erect a rod to suit himself, cannot go wrong in his choice of substances, such as ivory, dry wood, &c., nor can he go wrong if he only uses a conductor of a sufficiently large diameter. We believe the round rod is just as good as the square one, and the solid section, not the surface, is the main object. - The most important questions to be asked are, "what is the smallest diameter of rod that will suffice to form a good conductor, and what size of a building (area) will one rod protect." The last question is not easy to answer. Unless the chimneys of a house are very near together, a branch rod should be erected on each, extending two feet above them, and vertical branch points two feet above the roof should be placed within twenty five feet of one another. It is no easy matter to tell the size of the least cross section that will answer. E. Merriam, who has devoted much attention to the subject, asserts that No. 10 iron wire is sufficient, and that 100 feet of it can be purchased for one dollar. - Iron wire five-sixteenths of an inch in diameter, is the size used for our large public armed ships, and these have never failed to afford protection to the ship and to all on board.
As copper wire is eight-times a better conductor than iron, we prefer it. It costs only fifty cents per pound, and a good and perfect conductor made of copper wire can be put up for one shilling per foot. Excellent insulators can be made of wooden cleats varnished, painted, or boiled in oil, nailed with iron nails (covered with wax or varnish) to the building, and merely having holes bored in them for the wire to pass through. The copper wire will last ten times longer than an iron one; it should be pointed with a file, and not hammered. We feel no hesitancy in speaking of copper wire as being a cheap and reliable conductor, and we would trust to a section of it not more than three-eighths of an inch thick in preference to an iron wire of at least twice the diameter. There is not a man in our land who cannot erect his own lightning conductor, there being no great amount of science or art required; care and attention, with what we have said on the subject, will enable any man to put up his own lightning rod.