Faraday to Peter Henry Berthon   3 August 1864

Royal Institution | 3 August 1864

Sir

I return the drawings & papers which relate to the proposed creation of two electric lights at Portland¹. They refer almost entirely to the construction of houses, steam engines, water reservoirs, and other works; and touch but little on the principles of the light. It is, I conclude, understood, & may well be conceded that the light is effectual for light house purposes. Former reports have stated that as my opinion². I am very sorry that so beautiful a light is so expensive. I perceive that the estimate for mere outlay for the two Portland lights is above £8000. It is not for me in the present state of the matter to judge whether such an outlay with increased current expense & increased complexity is justified by the comparative deficiency in brightness & efficacy of the lighting by oil[.]

But a new circumstance is introduced into this case which was not present in the use of the electric light either at the S. Foreland or as now at Dungeness, and that is the great length of the conducting wires[.] The high light will require to be connected with the M.E. Engine by 700 yards of wire in two lengths one going & one returning they will be insulated but will be within 3 inches of each other under the earth. If they be not well insulated there will be a loss of electricity & illuminating power due to conduction;- if they were perfectly insulated there would be an inductive action the effect of which whether much or little upon such a disruptive current as that of the M.E. Engines I cannot estimate before the real trial. Results thus affected led Electricians to estimate the conduction of copper to vary as much as from 1 to 100. (Faraday Researches Vol III p.515³)[.]

In estimating the amount of steam Engine power required to rotate the M.E. machines it must be remembered that it is much affected by the manner in which the current is carried of[f] and used either at the light or elsewhere[.] Several cases unite in their effect but are very influential one is the good transmission & [word illegible] in the lamp. If that be interfered with, the power requisite to rotate the M.E. Engines will be diminished[.] I make these remarks now because it is difficult to give conclusions (from the data already obtained) for a case which has not as yet been realized⁴[.]

I am, Sir | Your Very humble Servant | M. Faraday

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