Warren De La Rue to Faraday   28 September 1857

110 Bunhill Row, | London E.C. September 28 1857

My dear Mr Faraday

I am greatly obliged to you for the copy of your paper on the relation of light to metals¹ which I have nearly read through - you have made a most interesting investigation of the phenomena, and will probably hereafter do much more in the same path. It was very scrupulous on your part to name me in your paper for the slight assistance I was able & glad to render².

The full moon was on the 4th of September, as you say,- but very early in the morning (5h. 7m AM.) and as the photograph was taken on the 7th at the 14-15 hour (the 8th at 3o clock AM) nearly four days had elapsed, so that fully one fourth of the moon was in shadow:- added to which those parts most in shadow do not produce a sensible impression on the plate by the time the lighter portions are overdone; So that all the lunar surface visible to the eye is not depicted:- the original photograph, however, shows a little more than the copies taken from it, but not quite all that could be seen with the eyepiece.

Do not hesitate to do what you require with the fragments of speculum metal, they are quite at your disposal. If you would like to cast them into other forms it is easily done and they are very readily polished quite true:- will you allow me to put you in the way of doing this? It is quite easy and you would have no difficulty in doing it yourself much better than you will get it done by another, curved specula are also very easy to make.

It is quite astonishing how much of the actinic rays is stopped by the atmosphere when the moon is situated, as it has been lately, at only a few degrees from the horizon - I could not obtain on the 25th the slightest impression of the moon in 25 seconds whereas in 5 seconds when well situated the plate is almost over done. A slight haze which barely diminished Jupiter’s light stopped so much of the actinic effects that I could not last night obtain the slightest trace of an image in 25 seconds under such circumstances, whereas in 12 seconds just previously I obtained a capital impression. I believe that there is room for a curious investigation in this direction. Did you try gold in its green & purple states in regard of its transmitting or excluding the actinic ray?

Yours Very truly | Warren de la Rue