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Correspondence.

The Editors are not responsible for the Opinions expressed by their Correspondents.

Lightning Rods.

MESSRS. EDITORS:—I notice an article in your paper (No. 3 current volume,)headed, "Are Pointed Lightning Rods any Protection?" Allow me to ask the question.  Is a lightning rod, as commonly erected, any protection at all? I wrote an elaborate article on this question, founded upon experience and observation, ten or twelve years ago, for the New York Tribune, showing that they were not only of no use but really a dangerous contrivance, often bringing the thunderbolt (electrical explosion) upon the building, when it would have gone some other place, had not the rod attracted it to the building.  I had a personal conversation with Prof. Henry soon afterwards on this subject, and he expressed the same opinion you quote, to wit: "The office of a lightning rod is to protect a building from a discharge from the heavens.  As a general thing its effect upon a distant cloud must be too small to silently discharge its redundant electricity, though in some rare instances it is possible that it may so reduce the intensity of the cloyed as to prevent a discharge, when, without such reduction, a discharge would take place."

That was the ground I had taken in my article, and upon that showed that the lightning rod did not fulfill its intended duty when it received electrical explosions, but in such cases frequently caused the shattering of buildings and setting barns on fire.  In a five years' record I kept of lightning strokes in Lancaster county, over two-thirds of the cases had lightning rods mounted, and six barns out of ten were burned to the ground with lightning rods mounted; that is, ten barns burned up, six of which were provided with rods and four had none.  About that time a large number of buildings in New York and Boston suffered from electrical explosions, although surmounted by rods, and it was these stubborn facts that induced me to give a widely published paper the science and facts in the case.  The only counter article on the subject that I learned of was from Mr. Quimby, who simply stated that the cases I made reference to "were not surmounted with rods of his construction!" Now for the facts of the science.  The discharge generally comes from the cloud to the earth.  When it passes within tractive distance of a tractor, which may be a lightning rod or other metallic prominence, or any projecting pointed wood or stone, it will fly to that, at an angle to its previous course.  When in such case it strikes the lightning rod it is like trying to knock the discharged cannon ball away from your person with the bayonet of your musket instead of drawing the charge from the cannon with the screw-rammer, or plugging up the prime-hole with a rat-tail file.

The legitimate office of the lightning rod is to draw the electrical surcharge from the cloud silently.  That is the only scientific efficiency of the lightning rod, and the question is, how far from its point will the rod disarm this pending surcharge of the electrical cloud? Clouds rarely come within fifty or one hundred feet of the tops of houses and barns, oftener over one thousand to fifteen hundred feet.  Will any electrician or lightning-rod maker claim for his rod the power of disarming a cloud one thousand feed about it.  Prof. Henry said that it may disarm it by induction.  I will not dispute this theory as applied within reasonable distance, say within fifty feet of the point of the rod.  Mr. A. George, of Philadelphia, a philosophical instrument maker, and myself saw a lightning rod illuminated at a point for several seconds at a time, one night when a thunder storm was passing over the city, but it was a remarkable condition of the atmosphere—hot and sultry, and the clouds appeared to be brushing the chimney tops.  That rod was performing its legitimate office. Prof. Henry mentioned to me a similar instance he witnessed on the rod of the Smithsonian Institution, nevertheless that building has been twice struck by electrical explosions, and the rods of it are put up in the most approved scientific order.  With the point of a penknife, or a cambric needle, you can draw the charge from the prime conductor of an electrical machine silently at a distance of ten or fifteen inches, but not that many feet, hence there is a very limited distance allotted to the withdrawing power of a lightning rod in drawing off a surcharge of electricity silently.

Tall trees near a building are better protectors to it than a rod surmounting the building. The top points of the tree, when elevated above the top of the building, will draw a "bolt" to the tree, though that bolt is moving toward the roof of the building. I examined one case where the bolt dashed into the top of a buttonwood tree standing in front of a one-story house: the house had a shingle roof, with a sheet of tin about four feet from the eaves, stuck in to replace a rotten shingle.  The electricity run down a main branch of the tree to its crotch, and tore off the bark there, and thence jumped over about fifteen feet and right on the sheet of tin above-mentioned, made a hole in the tin as if a chestnut burr had been fired through, turning down eight points of tin into spiral coils or burrs around the hole, and from there jumped four or five feed down to the tin water conductor, perforating that a dozen or more places about the size of No. 6 shot—running right and left on the water conductor, and at the closed end jumped to the cornice of the house, tearing off splinters and expending itself on the corner bricks; while at the other end it ran down the spout, jumping from its end eighteen inches onto an iron water pan, displacing that and burrowing into the earth under the pan to a depth of a foot.  There was no lightning rod, nor within two hundred feet of the building.  I examined a number of cases where tall trees drew the explosions away from the tops of buildings, as the directions of the bolts and the impact upon the trees plainly indicated. 

After a five year's investigation of the subject, I took the lightning rods down from two houses I owned looking upon them as decoy ducks to the errant thunderbolts that might change to happen in that direction.

A lightning rod, or protector from lightning, either from a pending surcharged cloud, or a bolt, to be efficient, should be elevated on a mast or pole as high as possible—better 150 feet high than 75 feet—and it ought to stand a little distance from the building or buildings, surmounted with a metallic ball and finely-pointed gold or platinum point; it will then silently draw off the surcharge from a proximate cloud, and will also draw a stray bolt to the ball and rod, that may be moving in the direction of the building.  By bolt or thunderbolt the intelligent reader will understand me to mean electrical explosions, in distinction from surcharges or surcharged cloud.  A bolt is exploded electricity; that is to say, the cannon ball shot out of Jupiter's gun, surcharges or surcharged cloud is the cannon ball lying quietly within the cavity of Jupiter's cannon, but ready to go off at any moment that the match of electrical traction comes within its reach. 

As regards the interruption of conduction by paints or other substances on the surface of a rod, I would say that I have often discharged an electrical battery with a pair of fire-tongs in my bare hand, and have never felt the least effect upon my hand.  A rough piece of iron would, no doubt, let some pass off laterally—the fire-tongs being smooth conducted it all.

Such are the stubborn facts, and science of the facts of electrical forces, as exhibited in thunderbolts and lightning rods, and if I have stated any controvertible points, they thould [[sic]] be pointed out for the benefit of mankind by someone better acquainted with the subject than your correspondent.

Lancaster, Pa.

JOHN WISE