Faraday to James Timmins Chance   4 September 1860

Royal Institution | 4 Septr. 1860

My dear Sir

I do not know how much room I shall want, so I take something larger than a sheet of note paper. Let me acknowledge yours of the 1st¹, and then say, that I was yesterday at the Trinity House, and was authorized fully to write to you in its name²; of which you will hear generally from the Secretary³:- and let me say at once, that in your reference to expence, and even of your own willingness to defray it for the good of the cause, that cannot be thought of for a moment. The Trinity House desire, by me, certain things to be done, both at your works and at Whitby; and of course will pay the expences⁴. I have told the Deputy Master⁵ that you were quite willing to help in every way that you could.

Focal Points. I have reported to the Trinity House my theoretical conclusions regarding a change in these⁶:- and the degree of change. I have also reported what you have done in respect of the lower reflectors;- have stated what I saw at your works, and my perfect satisfaction with the results as given by the Russian lights;- and have recommended a point 20mm above the burner and 50mm from the axis, towards the reflectors, as the focus hereafter to be used for the adjustment of the lower reflectors for a chief horizontal beam. The dip to be taken into account whenever that is necessary.

For the upper reflectors I have made a first report (by theory) of a point, 27mm above the burner and 32mm from the axis, on the side opposite to the reflectors. From certain experiments I made here with a very excellent lamp, I deduced a point, 30mm above the burner and 32mm from the axis. Now can you help us (I should not like to go elsewhere), by putting up a lamp and an upper pannel of reflectors, and adjusting the latter to this focus; I would then come down and we would see what the result is. The lamp I used was a very excellent one; perhaps too excellent to be taken as a standard; (though I see no reason why not). It burnt between 6 and 7 pints of oil in 4 hours⁷; but it was very steady and without smoke all the time. Still, I should be glad if you could adjust a second upper pannel of reflectors, to a focus 30mm above the burner and only 28mm from the axis; that we may make our experiments more decisive & instructive.

As to Whitby:- leave the North light as it is and deal only with the South light. I mentioned to you to put a new lamp, such as you approve and will be responsible for. It is our opinion that the person who supplies the optical part, ought to supply and be responsible for the lamp in future. Then readjust the lamp for the dioptric part, having respect to the dip to the horizon;- readjust the lower reflectors from the focal point decided upon to the sea horizon; and readjust the upper reflectors from the focal point we shall determine upon when you have the experimental pannels ready.

When however the Whitby light is thus adjusted, we want to make the experiment as instructive as possible. Now the light includes 180° of the horizon; and there are four sets of pannels or frames, each of about 45°. I propose to leave the first upright set of pannels unchanged (except for the dioptric part which will alter with the lamp); to correct the upper and lower reflectors of the second upright set, to the foci we shall determine upon:- to correct the reflectors of the third set to the other trial foci we shall adopt;- and to leave the fourth set of reflectors unchanged. Then in sailing round the lighthouse we shall have the successive observations and always the North light to refer to as a standard.

You have the Smalls light in hand. Though the time of the contract is drawing near, yet I am authorized to wish you to delay the adjustment of the parts, until we have determined the new foci. I need not say how glad I shall be to have the two experimental pannels ready for observation soon.

I fancy I shall have to come down to you soon to examine two Red sea lights for the Board of Trade. To give the power of examining them, (and lights generally) as I should like to do in the future;- even a fixed light ought to stand on a revolving platform;- for I shall want to observe from the flame place to a distant point which may (upon a scale) represent the horizon. Can this be?

You will probably have heard that the Russian Engineer wrote to me, and that I gave him my opinion on the lights.

I shall be very glad to hear & see your results as to the light thrown up into the air;- and all else (as you well know) that you obtain. The flame of a lamp is favourable as respects the sea light. We shall have more anxiety on that point with the electric light.

I may have to run up & down to & from Spon lane, but I must not be always a trouble to you. I must find some place near at hand, if we are always to examine the apparatus upon the works; and I certainly think that is best.

Ever my dear Sir | Most truly Yours | M. Faraday

James Chance Esq | &c &c &c