Faraday to Peter Henry Berthon   20 August 1858

Royal Institution | Aug 20. 1858.

Sir

I am now able to reply to your letter of the 14th instant¹ regarding the lime light of Major Fitzmaurice. I received an official letter from him on the 12th after which I felt it necessary to write a letter in reply (a copy of which I send you), that my position might be made quite clear²[.] I sent him also a copy of my letter to you of the 21st of July³ in which I stated what information I should desire & I asked (as you will see) for that information especially as regarded paragraphs 2. 3. & 4 which his letter of the 12th did not contain. I have received from Major Fitzmaurice his final communication dated 18th August (having returned to him by his desire his letter of the 12th) and now send it to you with the accompanying remarks[.]

The letter of Major Fitzmaurice does not give me any information in answer to my enquiries which at all modifies my opinion respecting the uncertain applicability of the lime light in lighthouses. That the lime light is very intense & beautiful is manifest to every one & its application in lighthouses has been often thought of, but the numerous circumstances & precautions regarding the manufacture storing & application of two different gases the kind of machinery required, the peculiar knowledge necessary, the comparative delicacy of the arrangements compared to those now in use to which would now be added the employment of that volatile & combustible substance camphorated ether & the lonely & out of the way position of the most important lighthouses are serious & opposing reason against any attempt to establish the light in a lighthouse until it has been wrought out perfectly on a full scale. I am not prepared to expect an applicable result satisfactory in all points; but if a discoverer says that he has & can realize such a result I should be very happy to see it done[.] I do not at present believe in the superiority of Sulphate of lime calcined &c as a medium over quick lime - nor in the assumed value of the addition of the camphorated ether: these are points which need proof, and in such trials would obtain either it or correction.

As to the price of the light namely six pence per hour that would require verification during the trials. Major Fitzmaurice states that his medium power light consumes from 3 to 4 cubic feet of mixed gases per hour. A lime light which I have used consumed very nearly 4 cubic feet per hour and gave light equal to that of 14½ oil argand lamps, that is to say it gave such light over one half of the horizon for as the lime is dark on one side and light only on part of the other it would require two if not three such lime lights to equal a central lamp equal to 14½ oil Argand lamps. The cost & value of the relative lights however can only be deduced after they have been compared on a full scale[.]

Major Fitzmaurice says in the 2nd paragraph of his letter that the lights can be practically applied as central lights for dioptric arrangements and it seems to me that this is the proper form for comparison with the Fresnel lamp both with & without lenses; but in such trial a single lime light will not be sufficient - the whole horizon must be filled as much as it is filled by the Fresnel lamp. I am not advising the Trinity House to make such a trial for I fear that even if the result promised well as a light, the numerous other circumstances before referred to would prevent its adoption. It is not as it appears to me the place of the Trinity House to disprove an insufficient plan but the duty of the Inventor to prove in all points a good & sufficient one. Nor should the Trinity House take upon itself in any degree the arrangement & conduction of the proof, since it would render itself liable to the charge of misrepresentation if the case failed - and might even unawares interfere with that perfect liberty & command on the part of the inventor which he might think necessary to his success. But the proof must in its nature be complete the mere exhibition of the light in a parabolic reflector is in my eyes of no lighthouse value⁴[.]

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

P.H. Berthon Esqr | &c &c &c