Frederick Madan to Faraday   8 November 1852

Trinity House | Novr: 8th:/52

My dear Sir

We have a considerable difference of opinion here relative to the expressions in your letter of the 26th: ulto:¹ stating the conclusion you come to as to the power of a second order annular Lense. You say “it would seem probable that 8 lamps & their reflectors would give beams of equal power to a second class light with 8 lenses”: or might probably surpass it. Now the Deputy Master² & some others understand you to mean from this, that one lamp & its reflector would be equal to one 2d order annular Lense, but this is so contrary to all I have hitherto heard, that I think they must misunderstand you. I have always heard that even Cookson’s³ 1st order Annular Lenses with the 4 wick lamps were about equal to ten lamps & Reflectors, & that the improved French Lense, which is 8 or 10 inches deeper, would be fully 10, or even 20 more; & from that I had concluded that a 2d order Lense would be equal to 6 or 8 Lamps & Reflectors. Pray let me know how this is. The area or measurement of the 2d order annular Lense will probably be 20 inches wide by 2F 6I deep, that is, of 8 to the circle, the same as the fixed Refractors. Those of 12 to the circle will of course be less wide.

Your’s sincerely | Fredk Madan

The Light Apparatus at the Caskets at present consists of 8 Reflectors in 8 faces, that is, only one Reflector on a face.

M Faraday Esq | &c &c