Frederick Madan to Faraday   11 November 1852

Trinity House | Novr: 11th: /52

My dear Sir

I am much obliged to you for your explanation¹.

I was absent in the yacht during nearly the whole of the month of Septr 1840, & was not present at the trials you mention², neither do I remember hearing the result of them. I had always understood, I think it must have been from my late Friend Drew³, that our Dioptric apparatus at the Start Point was considered equal to those at Beachy Head & St Agnes, the one being 1st order revolving, with Cookson’s⁴ Lenses & Mirrors, & the other having ten Reflectors on a face. This must be my excuse for the mistake I have made, but still I am inclined to think that my impression is more in accordance with Alan Stevenson’s⁵ experiments, & as it is an important question which are most eligible for a revolving Light, Reflectors or Lenses⁶, I shall observe to the Deputy Master⁷, when I show him your letter, that it would be very desirable for you to be furnished with a 2d order Lense, & whatever you may require to come to a correct conclusion.

In your letter you estimate the divergence of the Lense to be 15˚, the same as the Reflector;- I thought it had been 5˚ or 6˚ degrees.

I think also that Wilkin’s information as to the consumption of oil of the 3 & 4 wick lamps is not correct, & that our Mean here would make the one about 2/3ds of the other.

I should like to have the whole subject thoroughly investigated.

Your’s very sincerely | Fredk Madan

M Faraday Esq: | &c &c