At this season of the year we generally have some inquiries about lightning conductors, such as their best form, the best substance, its thickness, and how to erect them. What a change has taken place in the minds of men respecting lightning, since the discovery of it% identity with electricity by the philosophical Franklin. A bead of amber was, at one time looked upon as possessing a mysterious relation with the spirit world, hence the old oriental stories of magic rings, &c. The Roman soldiers looked with awe upon the lights that were often seen dancing on the points of their spears ; and sailors looked on with wonder at the gleaming fires—their " Castor and Pollux,"—which oftentimes played around the " main truck." The discovery_ot_elegtricity by Stephen' Gray, in 1720, a little over a century ago, m.rks an important era in physical science ; but the most important discovery connected with our text, was that made by Franklin to which we have alluded. This discovery was one of the most romantic with which we are acquainted in the whole history of philosophy. How grand the noble old philosopher printer looms up before the mind's eye, standing in his sober brown coat, gazing witk his calm contsmplative face, upward to the tiny kite which he had raised to lure the lightning Dolt from the dark thunder chariot, and lock it to the floor of mother earth. At that moment a new science was born—that of lightning conductors ; Franklin was the mo-dern Prometheus, who stole fire from heaven. Further researches proved that the earth and the air were equally under the influence of electricity, and that it was an all-pervading element. It was shown that no body existed in nature through which this subtle principle was not diffused,—that changes were constantly being produced by the interference; f other physical powers, and thus, in the efforts made to restore equilibrium, we hae manifestations of electrical phenomenon—lightning. During every stage of animal and vegetable growth, electricity is either absorbed or given off, and no change can take place in the form of matter without affecting a change in its electrical conditions. When water is converted into vapor by intense solar influence, electrical equilibrium is disturbed, and in nature's efforts to restore the lost balance between earth, and air, we have thunder storms. Electricity accumulates and floats in clouds, and unless it is quietly discharged or conducted back again to earth when the cloud becomes overcharged with its artillery, it bursts forth in fury, and sometimes proves very destructive to the persons and property of the children of men. When lightning strikes a tree, in passing to the earth from a cloud, it oftentimes splinters itinpieces ; it never passes by the solid matter upon which it falls ; it endeavors to find its way to the earth by the interstical spaces between the particles composing the olid object; when these channels are insufficient to convey it, they are thrown apart, and the tree, house, or other object struck, is split in all directions. There are certain bodies which, by their peculiar molecular construction, have the property of allowing this fluid to pass through them freely, and any of these bodies, of suffi-cient size to convey all the electricity of a thunder cloud to the earth, if placed in proximity to it, will pass the same as quietly and conveniently, and harmlessly, to the earth, as a pipe conveys rain water from the roof ot a building. These bodies are called lightning conductors ; Franklin was the first to apply them—his practical mind always looked to the useful, and this was one of his most useful discoveries. A copper or iron rod, erected to project above the highest point of a building, and conducted down to some moist part of the earth, performs, as we have stated, the same office for lightning that a gutter does for rain water in conducting it to a cistern from the roof a house. Copper makes the best lightning conductor—there is no fear of having it too thick: Faraday says, "the solid section is the grand object." It has hitherto been held by many to be a scientific fact, that the surface was everything in a lightning conductor, hence twisted iron rods and flattened strips have been erroneously employed in place of thick rods of uniform diameter throughout. If we take a wire, and form a galvanic circuit with a strong battery, if one part of the wire is thinned out, or is made of a different metal, such as an iron link in a copper chain, the thin part will be intensely heated, and so will the iron link. A lightning conductor, therefore, should be ot a uniform thickness below the upper point, and should be made ot one M*d of metal from top to bottom. An ironrod may be tipped at the point with silver or copper. The principle of constructing and putting up lightning conductors, is very simple ; any person can do so, or give directions to do so, who pays the least attention to the principles we have laid down. The thickness of an iron one, we believe, should at least be half an inch in diameter, but rather let it be a thick wire, than to have none at all. The stays to bind the conductor to a chimney or the side of a house, should be non-conductors, such as thin strips of metal driven into dry varnished pegs of wood, and the conductor should#always present the greatest amount of metal surface and section ; and it should terminate in some moist part ot the earth, such as a well or cistern. A good system of lightning conductors might protect any extent of country from thunder storms. Science is correct on this point, and in the South of France the vine growers now protect their vines from devastating hail storms produced by the sudden congelation of the water of the rain cloud when robbed of its latent heat by sudden electrical discharges. This hey do by raising lightning conductors over their gardens ; where these are plentifully distributed, hail storms are now scarcely known m places where, at one time, they were quite frequent. So much has man gained by the flight ot a kite from the hands of an American philosopher.
This article was originally published with the title "Lightning Conductors" in Scientific American 8, 35, 277 (May 1853)