Faraday to Jacob Herbert   24 March 1853

Royal Institution | 24 March 1853.

My dear Sir

In reference to the proposition made on the evidence which you sent to me given by Mr. Gordon on the subject of the fog signal¹ I think I understand that the proposed arrangement has not been really tried but is suggested on the score of the analogy between light and sound. In my opinion it would not be prudent to substitute an untried method in a case of actual service for such as have been tried, the best of which would of course be selected.

If I were asked what results I should expect from experimental trials; with a view of testing the proposition and producing a good & useful apparatus in conformity thereto, I should say that the results are doubtful and that it would require many trials & reconstructions of the apparatus before either an affirmative or a negative result would be obtained. I do not as yet know of any thing approaching to a steam whistle either in power or arrangement of parts which has been obtained by a bellows yet something like such a source would be required not merely in respect of strength of sound but also of form and consequent distribution of the sonorous undulations. A steam whistle sends sounds of nearly equal intensity in all directions around it; any arrangement having the form of an ordinary whistle does not do so; and would not be so fit for a central source as the former.

Then as respects the reflexion of sound the origin of which is in a focus:- though the physical analogy of light and sound is very great, yet there is an infinite difference in degree between them, and we have no material which is to sound what polished silver is to light. In the absence of previous experience & trials it is even possible and most probable that the first acoustic reflectors found for such a purpose might deaden & destroy sound and that to a large extent. On the other hand if by investigation a constant & useful mode of construction could be discovered and the best material be ascertained, still the curvature and the size of the reflectors which would be required are altogether unknown, & would need further experiments for their determination[.]

So that at present if any one were to propose to work out such a system as that described by Mr. Gordon I should not object on the score that the proposition was unphilosophical or against natural principles but I should say experimental investigation would in the first place be required & I should not be surprized if he failed to eliminate any practical or applicable result²[.]

I am My dear Sir | Very Sincerely Yours | M Faraday