Faraday to George Herbert   27 August 1862

Royal Institution 27 August 1862

Sir

I received your letter of the 22nd instant¹. I do not know whether the lime light company intend by their answer to the 24th question to ask for further progress but if they do submit the following considerations thereon.

The numbers refer to the questions & answers contained in the paper dated 4th of August 1862². Answers 2. 3. 4. relate to any essential difference between the proposed and former lime light. The Compy. refer to stability. No want of stability appeared during the trial of the former lime lights in the lighthouses.

No. 13. describes the lime as being in the form of a disc the size of an ordinary plate:- the focus of light is described <(16)> as an intensely heated point about one tenth of an inch in diameter: it is to be expected that this focus will be slightly depressed below the surface of the lime plate. The light from such a point cannot radiate in all directions - it cannot be seen at all except within 180° it cannot send forth equally intense rays through 90° or even 45°. How therefore a single disc of lime with one jet or with several jets, or how several discs are to be combined into a central light, does not yet appear. The Trinity house desire before any other proceedings are taken in the matter to be informed on these points.

No. 20 question refers amongst other things to lighthouses in central situations i.e. to such as are required to illuminate many degrees round the horizon[.] The answer does not seem satisfactory.

The experience the TH has obtained by long lighthouse practice teaches them that if the above observations were answered in an apparently satisfactory manner still the final judgment could only be obtained by a real lighthouse experimental practice. The following questions would all require such illustration & support 2.3.4.5.6.7.8.9.10.11.12.13.14.17.18.19.20.22.23.24. Judging by the past experience they do not expect a satisfactory result, and cannot undertake to determine what the result will be, but if desired by the Company they are willing to give it the same opportunity that was given to other parties - i.e to pay a certain sum for the light of the four next winter months November December January February; for the Upper light at the S Foreland where the illumination is to extend round + 270 degrees of the horizon[.] This must be done in a practical working manner; without failure in gas,- without accidental extinction,- without failure of light in any other way,- with ordinary attention, and so as to give, by a practical result, the outlay required & the current expence. It must also be done so that if the light should go out or be deranged during the trial the ordinary oil lamp may be instantly placed by the keepers in its right position. And if at any time the T.H may deem the experiment a failure, or consider that the service of the light is insufficiently performed, they reserve the right to require the immediate removal of the apparatus³[.]

I am Sir | Your Very Obedient Servant | M. Faraday

Geo Herbert Esqr | &c &c &c | Trinity House

+ (I am away from home & doubtful whether 270° is enough,- better say too much than too little. MF)