A letter from Ben Franklin to David Hume about how to set up a lightning rod to protect your building from the “mischiefs of lightning”. Given North Carolina’s high frequency of lightning strikes, maybe I should follow this advice.
In Compliance with my Lord Marishall’s Request,2 communicated to me by you when I last had the Pleasure of seeing you,3 I now send you what at present appears to me to be the shortest and simplest Method of securing Buildings, &c. from the Mischiefs of Lightning.
Prepare a Steel Rod 5 or 6 Feet long, half an Inch thick at its biggest End, and tapering to a sharp Point, which Point should be gilt to prevent its rusting. Let the big End of the Rod have a strong Eye or Ring of half an Inch Diameter: Fix this Rod upright to the Chimney or highest Part of the Building, by means of Staples, so as it may be kept steady. Let the pointed End be upwards, and rise three or four Feet above the Chimney or Building that the Rod is fix’d to. Drive into the Ground an Iron Rod of about an Inch Diameter, and ten or twelve feet long, that has also an Eye or Ring, in its upper End. It is best that this Rod should be at some Distance from the Foundation of the Building, not nearer than ten feet if your Ground will allow so much. Then take as much Length of Iron Rod, of about half an Inch Diameter, as will reach from the Eye in the Rod above to that in the Rod below; and fasten it securely to those Rods, by passing its Ends thro’ the Rings, and bending those Ends round till they likewise form Rings. This Length of Rod may either be in one or several Pieces. If in several, let the Ends of the Pieces be also well hooked to each other. Then close and cover every Joint with Lead, which is easily done by making a small Bag of strong Paper round the Joint, tying it close below, and then pouring in the melted Lead. It being of Use in these Junctures, that there should be a considerable Quantity of metalline Contact between Piece and Piece: For if they were only hook’d together, and so touch’d each other but in Points, the Lightning in passing thro’ them might melt and break them where they join. The Lead will also prevent the Weakening of the Joints by Rust. To prevent the Shaking of this Rod by the Wind, you may secure it by a few Staples to the Building till it comes down within ten feet of the Ground, and thence carry it off to your Ground Rod; near to which should be planted a Post, to support the Iron Conductor above the Heads of People walking under it. If the Building be large and long, as 100 feet or upwards, it may not be amiss to erect a pointed Rod at each End, and form a Communication by an Iron Rod between them. If there be a Well near the House, so that you can by such a Rod form a Communication from your Top Rod to the Water, it is rather better to do so than to use the Ground Rod above-mentioned. It may also be proper to paint the Iron, to render it more durable, by preserving it better from Rust.
A Building thus guarded, will not be damaged by Lightning, nor any Person or Thing therein kill’d, hurt or set on fire. For either the Explosion will be prevented by the Operation of the Point, or, if not prevented, then the whole Quantity of Lightning exploding near the House, whether passing from the Cloud to the Earth or from the Earth to the Cloud, will be convey’d in the Rods. And though the Iron be crook’d round the Corners of the Building, or make ever so many Turns between the upper and lower Rod, the Lightning will follow it, and be guided by it without affecting the Building.