Faraday to Jacob Herbert   25 September 1843

Report on the Lightning Rods of Light Houses.

The Undersigned¹ have, according to their Instructions, met and consider'd the circumstances under which Light Houses are placed as respects Lightning, and have arrived at the following conclusions.

That Light Houses should be well defended from the top to the bottom.

That, as respects the top, the metal of the Lanthorn and upwards is sufficient to meet every need and satisfy every desire and fear.

That, for the rest of the course of the Tower a copper rod 3/4 of an inch in diameter is quite and more than sufficient.

That at the bottom where the rod enters the earth, it is desirable at it's termination to connect it metallically with a sheet of copper 3 or 4 feet long by 2 feet or more wide; the latter to be buried in the earth so as to give extensive contact with it.

That glass repellers are in every case useless.

That glass thimbles are not needed but do no harm.

That if the repeller be removed and the point on the vane be terminated as the Lightning rods usually are, and then the metal of the Lanthorn be strongly attach'd to, and connected with, the upper end of the copper rod, and the rod continued down the Tower to the earth, and the sheet of copper buried in it, such a system will be an effectual and perfectly safe Lightning conductor.

That then there need be no rod end rising by the side of, and above, the lantern.

That the rod may (if required on other accounts) come down on the inside of the building, or in a groove in the wall, but should not be unnecessarily removed from observation and inspection.

That all large metallic arrangements in the stone work or other nonmetallic parts of the tower of the Light House, such as tying bars, metal flues &c. should be well connected by copper with the conductor.

That the vicinity of two metallic masses without contact or metallic communication is to be avoided.

That as to the South Foreland High Light, the Lanthorn, the central stone, and the copper rod proceeding from it to the earth, connected as they now are, form a perfect Lightning conductor even without the rod that is there erected; but

That it is important casual arrangements should never be depended upon for Lightning conductors, but a copper rod be establish'd for the especial purpose:- For if the former be trusted to, the carelessness or ignorance of workmen may, at after periods upon occasions of repair or cleansing, cause the necessary metallic connection to be left imperfect or incomplete, and then the arrangement is not merely useless but dangerous.

That as to the Eddystone it is desirable to connect the system of wrought Iron ties in it with the Lightning conductor, by joining the lower part of that Iron rod which is nearest to the conductor with the latter, by a copper rod or strap equivalent to the conductor in sectional area.

That the Dungeness Light House is in a very anomalous condition; to rectify which the two repellers should be removed and also the representative of the top of a Lightning rod attached to the flue:- and that then a good copper conductor should be attach'd to the metal of the Lanthorn, upon the principles already express'd².

25th September 1843.

(signed) M. Faraday

Jacob Herbert Esq | &c &c &c