Faraday to Robert Gordon   17 May 1861

Royal Institution | 17 May 1861

Instructions for Visiting Committee for lighthouses

My dear Admiral

I have waited a little while to see what the note from Mr. Berthon which you refer to, might say, but not having received any, write to you in reply to yours of the 15th¹.

The experiments which I have seen lately made at the Trinity House by Captains Nisbit [sic] & Baily² [sic] with four different lamps namely Chances - Grisnez - Le Grand - and Fountain each under the care of its special & specially interested keeper; fully confirm me in the opinion which I had before found that the principle of each lamp was right if properly carried out:- and that the care of the lamp was the essential matter:- in fact that a careful and intelligent keeper would cause any of the four lamps to do full duty.

I presume that the Committee of which you speak will before all things see that the lamp is good & in good order, and burns well, with a constant condition for sufficiently long periods of time:- not requiring frequent trimmings of cottons, or adjustment; having a good overflow, a well shaped glass; & an average height of bright flame rising from 3 to 3½ inches above the burner without counting to the top of the forks or tongues or much above where they separate from the body of the flame.

I suppose, that, next, the Committee will examine the relative consistency of the optical parts of the apparatus & by the observation of the horizon or objects at sea, & the use of the photometer or any other fixed appliance at the burner, will see whether the parts act in unison as one great whole.

Then the adjustment of the lamp concentrically with the optical apparatus, & also in relation to the height of the burner, has to be considered; and hoping that such flames may be obtained in the lighthouses as were procured at the Trinity house with all the four lamps; my opinion is, that the top of the burner should be 22-24 millimeters below the horizontal focal plane of the central band of the apparatus, and that a correction in height should be added, for the elevation of this plane above the sea horizon; according as that may be necessary for each particular lighthouse, & according to the tables already sent to the Trinity house by Mr Chance.

Having determined the place of the flame for the central or dioptric part of the apparatus, its relation to the upper & lower reflectors should be observed; and any corrections that may appear to be necessary, considered.

Above all it is important to establish a system by which an intelligent & secure watchfulness shall be obtained for the lamp, so that its flame shall not fade during the night, & so that the occurrence of any deficiency in its power shall be immediately reported & corrected. I am fully persuaded that an intelligent man instructed in the matter & the nature of the lamp will have far less trouble than another man who deals with the light as that of a common lamp and is continually setting it in order; not knowing or learning the management by which the lamp will keep itself in the right condition[.]

Special and smaller matters may require observation at any or every light house but I need not imagine these. Nor would I have written the above except at your request, for I have full confidence in the Gentlemen whose names I mentioned in the beginning of this letter, as to their knowledge of the principles concerned & their power of taking all these things into their consideration[.]

I am | My dear Admiral | Ever Your faithful Servant | M. Faraday

Admiral Gordon | & & &