Faraday to Peter Henry Berthon   19 December 1863

Royal Institution | 19 Decr. 1863

Sir

At last I am able to supplement my letter of the 20 Aug¹ relating to the extinction of the lamps in the lower lanthorn of the Lundy lighthouse during a storm which happened on the 1st of that month. The effect was referred by the keeper to a powerful flash of lightning and though there is no other evidence, by injury to the building, that the house was struck at the time, yet I am inclined to admit the correctness of the conclusion.

The nine lamps in the lower lanthorn are ventilated by pipes which, gathering all the burnt air & smoke together deliver it by a pipe 3¼ inches in diameter just under the roof of the lanthorn (see vertical section at C) into a larger pipe 5 inches in diameter, which is continuous to the upper lanthorn, & being there conjoined to the chimney of the stove, is, by it in communication with the air outside. I think that when the lightning struck the building the air in this tube was thrown into a sudden vibration; and there being no deflector plate over the mouth of the entering smaller tube (at C), that the oscillation was continued down the individual tubes to the lamp glasses, & by a momentary reversion of the current of air at the burning collars, extinguished eight of the nine lights. When ventilating pipes were first applied in practice there was such a deflector plate, fixed about an inch above the top of the entering pipe; and the bottom of the larger pipe was made funnel shaped. If that had been the case here, I do not think the lights would have been disturbed: for the precaution is quite effectual against gusts of wind or shutting of doors.

The ventilating copper tube enters the bottom of the stove pipe in the upper lanthorn but there is no damper or valve there, to render it independent of the stove, when that is not in use. I think there ought to be.

The water from the burnt oil of the lamps which condenses in the upper part of the ventilation pipe, occasionally runs out at the joints, and disfigures the exterior: this is because they are in the wrong direction. Within the house the lower end of an upper piece of pipe should enter into the upper end of a lower piece, and then the condensed water would flow onwards & downwards within. Provision should be made to collect the water at, I think, two places A & B (see Vertical Section) to meet the differences of temperatures & condition due to summer & winter[.]

The lightning conductor seems to have been very effective in its power²

I am Sir | Your Very obedient humble Servant | M. Faraday

P.H. Berthon Esqr | &c &c &c