Faraday to Peter Henry Berthon   8 March 1864

Royal Institution | 8 March 1864

Sir

I have received your letter¹ and the drawings referred to & have seen Mr Douglas and have had the advantage of his conversation regarding his proposition of building a lighthouse lanthorn with vertical steel standards of the dimension given. Considering the strength of steel I have no doubt that the material proposed is strong enough but I am not sufficiently acquainted with the principles of construction to give an opinion on the method described or to say it is unobjectionable.

That the use of vertical standards would greatly facilitate the accurate fitting of all the parts of the frame & the glass would I think be a great advantage[.] The proposed alternation of the steel uprights would diminish the amount of shadow cast by them but whether that would be sufficient to render the effect of inclining the standards of little or no consequence could be best judged of by such an experiment at the Trinity house as that proposed by Mr. Douglas at the close of his observations dated 2 March 1864[.]

Your letter asks me whether with such steel standards as those proposed the armature of the lens might not be placed so as to come intermediately between them with greater practical benefit than if placed optically coincident with them as at present[.] If the question is directed towards the amount of shadow cast towards the sea then I should answer No. Supposing the opaque bars do not optically coincide then all the shadow that they can cast sea ward is sent in that direction whereas if they overlap, so much shadow as is cast by one part on another is saved from the sea, & the sea illumination is by so much the greater[.] This is a point which could easily be shewn by the same experiment as that before referred to[.]

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

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