Faraday to Robert Gordon   18 October 1860

The Green | Hampton Court | 18 Octr. 1860

My dear Admiral

In reference to your enquiry at our parting at Whitby I may now say that the experiments in London Birmingham & Whitby which you allowed me to enter upon & carry out have been very successful and useful. They have enabled me to decide upon a departure from the focal regulations of the French authorities: and the comparison of the French regulations with three others has been practically carried out. You, with the Trinity brethren & members of the Royal Commission have seen the result both at Sea & on land;- have approved I believe unanimously of the change proposed and you have given orders accordingly.

The change consists in the first place in directing the chief & guiding ray to the sea horizon & not to the horizontal horizon or dead level and in the second place in altering the focus for the upper reflectors from a point 38m.m up in the axis of the flame to another 28mm up and 30 on one side;- and that for the lower reflectors from a point 9mm up and 50 aside to another spot 25mm up & 40 aside; the latter change being finely determined by experiments on Monday last¹. The result is that much of the light which would be directed by the French adjustments up into the sky by the new arrangement brought down & spread over the sea between the horizon & shore;- without any sacrifice of light at the sea horizon itself. Proof was obtained at the same time of the kind of lamp best suited in the service and the watchfulness required upon the part of the keepers respecting its action & proper condition[.]

The experiments have led to a refined mode & nicety of adjustment which can be practised by the manufacture with facility; nor need the Trinity house hesitate to demand a degree of accuracy which could not heretofore be called for. They have also shewn the value of the final examination of the optical apparatus within the lighthouse as recommended by the R Commission and under the exceedingly frequent obscurity of the Sea horizon how best to carry it into effect. New instruments as well as a new process have been invented and I cannot but express most earnestly my thanks for the manner in which Mr. Chance has enabled me by his own personal thought & exertions to pursue these experiments both at Birmingham & at Whitby to the best practical results.

I have the honor to be | My dear Admiral | Your faithful Servant | M. Faraday

Admiral Gordon | &c &c &c &c