Frederick Madan to Faraday   23 August 1842

Trinity House | Augt 23d 1842

My dear Sir

Being extremely desirous that our new Light Apparatus at Lundy should be quite perfect, & feeling sure that you are equally so, I have no scruple in troubling you on the following point respecting it.

The present Reflectors are 549 feet above high water mark, & I believe the Lamp of the new Apparatus will be a foot or two higher, or at least 550 feet. Now by the Tables the depression or dip of the Horizon at that altitude is about one degree, & the distance the Light will be visible from the deck of even the smallest vessel is above 30 miles. I want therefore to ask your opinion whether you do not think some allowance should be made on acct of the great altitude, for, as far as I can make out from Mr. Wilkins, none is at present intended. If my idea is correct, the Focus of the Annular Lense does not exceed 5˚, consequently if the rays of light travel exactly horizontally, there will be 3˚ 1/2 above the horizon & only 1˚ 1/2 below it; & vessels within a certain number of miles of the Island, will be completely under it. I represented this to Captn Welbank¹, who is now Chairman of the Light Committee, some time ago but he has done nothing, & I cannot feel satisfied without writing to you.

The main question is, do the rays of light travel horizontally or not? & of this you will be the best judge.

If they do, it would surely be advisable to depress the Mirrors & Lenses one if not two degrees, that as little as possible of the Focus may be thrown away in the air, & that in foggy weather there may be a fair strength of light near the Island. This is of course a consideration of much greater importance in a refracting, than it is in a reflecting light, as the Focus is so much smaller.

Lundy is by much the most elevated Light we have, indeed it is the highest I am acquainted with, except that on Barra Head in Scotland.

I called at the RI last week, but you were out of town[.]

Your's very truly | Fredk Madan