Faraday to William Crane Wilkins   27 October 1862

R. Institution | 27 Octr 1862

Sir

I cannot understand from your last note¹ whether when the lamp is raised 2mm to suit the elevation (the focus of the lens also being raised 2mm to correspond with the lamp) the foci of the upper & lower reflectors are to be raised or not. The last note refers to the second note for the reflector foci and they are there given in reference to the horizontal plane. Are these foci to be altered or not in consequence of the elevation of the lamp? and what is to be the elevation above the lamp burner of the three foci for the

Upper reflectors

Lens

and lower reflectors

I am sorry to give such trouble but these data are required by the Trinity house that they may consider & approve of them[.]

Very Truly Yours | M. Faraday

W. Wilkins Esqr