Benjamin Franklin on Lightning Rods in 1750

Benjamin Franklin believed that a lightning rod would help people to avoid lightning-damage from serious storms.  He described his ideas to Peter Collinson, one of Franklin’s British friends.

Part of Franklin’s letter to Collinson, about lightning rods, was reprinted in the May 1750 issue of Gentleman’s Magazine.  Historians believe that Franklin likely penned the letter on the 2nd of March, 1750.

Franklin references his Pamphlet about electricity which was about to be published.  The whereabouts of the original letter to Collinson is unknown, and historians believe this article is the first pubic record of Franklin’s lightning-rod ideas.

People writing English, in the 18th century, used a form of “s” which is no longer used.  As a result, reading 18th-century documents can be tricky for today’s English readers.  To make this document more understandable, here is its full content:

A curious Remark on ELECTRICITY; from a Gentleman in America; whose ingenious Letters on this Subject will soon be published in a separate Pamphlet, illustrated with Cuts [woodcuts].

Extract of a Letter to Mr P.C. F.R.S. [Peter Collinson, Fellow Royal Society]

I was very much pleased with some ingenious papers in the late Transactions on the subject of electricity.

There is something however in the experiments of points, sending off, or drawing on, the electrical fire, which has not been fully explained, and which I intend to supply in my next. 

For the doctrine of points is very curious, and the effects of them truly wonderfull; and, from what I have observed on experiments, I am of opinion, that houses, ships, and even towns and churches may be effectually secured from the stroke of lightening by their means; for it, instead of the round balls of wood or metal, which are commonly placed on the tops of the weathercocks, vanes or spindles of churches, spires, or masts, there should be put a rod of iron 8 or 10 feet in length, sharpen'd gradually to a point like a needle, and gilt to prevent rusting, or divided into a number of points, which would be better—the electrical fire would, I think, be drawn out of a cloud silently, before it could come near enough to strike; only a light would be seen at the point, like the sailors corpusante [(corpo santo) or, put differently, St. Elmo’s fire]. This may seem whimsical, but let it pass for the present, until I send the experiments at large.

Second page of May 1750 Article Reprinting Benjamin Franklin's Lightning-Rod Letter 

Second page of the Gentleman's Magazine article reprinting Benjamin Franklin's lightning-rod theories.

I shall further remark on the Transactions, &c. that the leaf gold suspended is not always nearest the non-electric, and that its situation depends on the number, acuteness, or situation of its points.  By cutting a leaf into the shape underneath [the drawing seen in the article, depicted above], it may be made to rest in the air, at any required distance from the electrified plate, from a quarter of an inch to a foot, while the nearest non-electric (the floor) may be at 3 or 4 feet distance.

If it draws too near the electrified plate, make the top more sharp; if it keeps at too great a distance, make it more dull, or obtuse, by cutting off its points; then, by tryals and a little practice, it may be made to rest where desired.

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Media Credits

Text images, described above, online courtesy Library of Congress.




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