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There the lightning made a hole through the wall, or back of the chimney, to get to the gun-barrel,* down which it seems to have passed, as, although it did not hurt the barrel, it damaged the butt of the stock, and blew up some bricks of the hearth. The brass wire below the hole in the wall remained good. No other damage, as I can learn, was done to the house. I am told the same house had formerly been struck by lightning, and much damaged, before these rods were invented."
Mr. William Maine's Account of the Effects of the
Lightning on his Rod, dated at Indian Land, in South Carolina, August 28th, 1760.
.....“I had a set of electrical points, consisting of three prongs,
of large brass wire tipt with silver, and perfectly sharp, each about seven inches long; these were riveted at equal distances into an iron nut about three quarters of an inch square, and opened at top equally to the distance of six or seven inches from point to point, in a regular triangle. This nut was screwed very tight on the top of an iron rod of about half an inch diameter, or the thickness of a common curtainrod, composed of several joints, annexed by hooks turned at the ends of each joint, and the whole fixed to the chimney of my house by iron staples. The points were elevated (a) six or seven inches above the top of the chimney; and the lower joint sunk three feet in the earth, in a perpendicular direction.
“Thus stood the points on Tuesday last, about five in the evening, when the lightning broke with a violent
* A more substantial conductor.
explosion on the chimney, cut the rod square off just under the nut, and, I am persuaded, melted the points, nut, and top of the rod, entirely up; as, after the most diligent search, nothing of either was found (b), and the top of the remaining rod was cased over with a congealed solder. The lightning ran down the rod, starting almost all the staples (c), and unhooking the joints without affecting the rod (d), except on the inside of each hook where the joints were coupled, the surface of which was melted (e), and left as cased over with solder. No part of the chimney was damaged (f), only at the foundation (g), where it was shattered almost quite round, and several bricks were torn out (h). Considerable cavities were made in the earth quite round the foundation, but most within eight or nine inches of the rod. It also shattered the bottom weather-board (i) at one corner of the house, and made a large hole in the earth by the corner post. On the other side of the chimney, it ploughed up several furrows in the earth, some yards in length. It ran down the inside of the chimney (k), carrying only soot with it, and filled the whole house with its flash (1), smoke, and dust. It tore up the hearth in several places (m), and broke some pieces of China in the buffet (n). A copper tea-kettle standing in the chimney was beat together, as if some great weight had fallen upon it (); and three holes, each about half an inch diameter, melted through the bottom (p). What seems to me the most surprising is, that the hearth under the kettle was not hurt, yet the bottom of the kettle was drove inward, as if the lightning proceeded from under it upwards (9), and the cover was thrown to the middle of the floor (r). The fire-dogs, an iron loggerhead, an Indian pot, an earthen cup, and a cat were all in the chimney at the time unhurt, though a great part of the
hearth was torn up (s). My wife's sister, two children, and a negro wench were all who happened to be in the house at the time; the first and one child sat within five feet of the chimney, and were so stunned, that they never saw the lightning nor heard the explosion; the wench, with the other child in her arms, sitting at a greater distance, was sensible of both; though every one was so stunned that they did not recover for some time; however, it pleased God that no farther mischief ensued. The kitchen, at ninety feet distance, was full of negroes, who were all sensible of the shock; and some of them tell me, that they felt the rod about a minute after, when it was so hot that they could not bear it in hand.”
Remarks by Benjamin Franklin.
The foregoing very sensible and distinct account may afford a good deal of instruction relating to the nature and effects of lightning, and to the construction and use of this instrument for averting the mischiefs of it. Like other new instruments, this appears to have been at first in some respects imperfect; and we find that are, in this as in others, to expect improvement from experience chiefly; but there seems to be nothing in the account, that should discourage us in the use of it; since, at the same time that its imperfections are discovered, the means of removing them are pretty easily to be learnt from the circumstances of the account itself; and its utility upon the whole is manifest.
One intention of the pointed rod is, to prevent a stroke of lightning. (See pages 313, 356.) But, to have a better chance of obtaining this end, the points should not be too near to the top of the chimney or highest part of the building to which they are affixed,
but should be extended five or six feet above it; otherwise their operation in silently drawing off the fire (from such · fragments of cloud as float in the air between the great body of cloud and the earth) will be prevented. For the experiment with the lock of cotton hanging below the electrified prime conductor shows, that a finger under it, being a blunt body, extends the cotton, drawing its lower part downwards; when a needle, with its point presented to the cotton, makes it fly up again to the prime conductor; and that this effect is strongest when as much of the needle as possible appears above the end of the finger; grows weaker as the needle is shortened between the finger and thumb; and is reduced to nothing when only a short part below the point appears above the finger. Now, it seems, the points of Mr. Maine's rod were elevated only (a) six or seven inches above the top of the chimney; which, considering the bulk of the chimney and the house, was too small an elevation. For the great body of matter near them would hinder their being easily brought into a negative state by the repulsive power of the electrized cloud, in which negative state it is that they attract most strongly and copiously the electric fluid from other bodies, and convey it into the earth.
(6) Nothing of the points, &c. could be found. This is a common effect. (See page 358.) Where the quantity of the electric fluid passing is too great for the conductor through which it passes, the metal is either melted, or reduced to smoke and dissipated; but where the conductor is sufficiently large, the fluid passes in it without hurting it. Thus these three wires were destroyed, while the rod to which they were fixed, being of greater substance, remained unhurt; its end only, to which they were joined, being a little melted, some of the melted part of the lower ends of those wires uniting with it, and appearing on it like solder.
(c) (d) (e) As the several parts of the rod were connected only by the ends being bent round into hooks, the contact between hook and hook was much smaller than the rod; therefore the current through the metal, being confined in those narrow passages, melted part of the metal, as appeared on examining the inside of each hook. Where metal is melted by lightning, some part of it is generally exploded; and these explosions in the joints appear to have been the cause of unhooking them, and, by that violent action, of starting also most of the staples. We learn from hence, that a rod in one continued piece is preferable to one composed of links or parts hooked together.
(f) No part of the chimney was damaged; because the lightning passed in the rod. And this instance agrees with others in showing, that the second and principal intention of the rods is obtainable, viz. that of conducting the lightning. In all the instances yet known of the lightning's falling on any house guarded by rods, it has pitched down upon the point of the rod, and has not fallen upon any other part of the house. Had the lightning fallen on this chimney, unfurnished with a rod, it would probably have rent it from top to bottom, as we see, by the effects of the lightning on the points and rod, that its quantity was very great; and we know that many chimneys have been so demolished. But no part of this was damaged, only (f) (g) (h) at the foundation, where it was shattered, and several bricks torn out. Here we learn the principal defect in fixing this rod. The lower joint, being sunk but three feet into the earth, did not, it seems, go. low enough to come at water, or a large