Faraday to Peter Henry Berthon   29 December 1859

Royal Institution | 29. Decr. 1859.

Sir

I have examined the two dioptric apparatus to which your letter of the 23¹ referred and which are I believe intended for Vancouver island. I find them excellent. The glass is perfect as to colour and relatively very free from striae especially in the central & more important parts. It is well wrought as to finish and shape so that the various parts (no less than 580 in number in the larger one) are perfectly accordant in their optical action so as to send a fine ray forward in the right direction[.] The larger apparatus is constructed to give 20 flashes in one revolution. This involves the use of 20 pannels with their metal frames & the consequence is that one ninth of the light falls on these frames & is cut off[.] Nevertheless as far as I am able to judge not more metal has been employed than is sufficient to give the required stability & strength to the whole structure[.]

I have the honour to be Sir | Your faithful humble Servant | M. Faraday

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