Faraday to George Herbert   22 September 1863

Royal Institution | 22 Septr. 1863.

Sir

The letter from Mr Chad¹ which you have sent to me is very creditable to him inasmuch as it shows a certain degree of acquaintance with the elementary principles of a branch of science not commonly known to men of his standing or occupation. But it also shows that he has had no opportunity of becoming practically acquainted with the application of electricity which he proposes or has made any experiments tending to show that the Electric lamp which his drawing & writing describes is in any respect superior to those which already exist or indeed is even possible as a matter of construction.

The Galvanic battery or source of Electricity referred to is not indicated as to its construction or principles either in the M.S or the drawing[.] From what I know of Galvanic batteries I do not expect any thing available for lighthouse purposes: and from the Experimental trials on a large & sufficient scale made at the Trinity house under the personal care & attendance of Dr Watson² with his batteries & appliances, I think the authorities of the Trinity House will be of the same mind (See Report 15 Aug 1854³.)

As Electricity supplied by the Magneto electric machine is however available in lighthouses, Mr Chad may perhaps think of his apparatus in connexion with such a source:- and therefore I proceed to make a few remarks on the proposition. The lamp is recommended for its merits and is said to be inexpensive in construction, simple in its action, and steady in light (except for variations in battery action)[.] The wording of the description leads one to suppose that the lamp has been constructed tried & proved and further that no objections to it in principle or practice have been discovered or if they have that they have been removed. I do not think that this is the case. I cannot pretend to point out theoretically the objections to the construction as they appear in reading the description and in the present state of matters my answer would be quite sufficient if I were to say that it will not succeed in a lighthouse nevertheless I refer to one or two points amongst others needing investigation or verification.

The carbons a.b. and c.d. in the drawing are considered as sliding in two fixed metallic tubes AB and CD with a contact & friction so slight that the small weight I suspended by a cord on the small axle E.F. is sufficient to overcome it. Now the whole electric current of the batteries which is to sustain the light has to pass from the metal tubes to the carbons within: that this may take place without injury to the apparatus we have in all such cases to jam or screw the metals & the carbons together else the spark passes, ignition takes place, & the carbons & tube are burnt & destroyed.

The Carbons (with a Galvanic battery) do not take or keep the shape which is given to them in the drawing but are made like the sketch; & the direction of the rays of light are not as those represented. The case of Magneto electric machines as sources of Electricity gives two distinct kinds of main illumination currents: the one kind consists of innumerable intermitting small currents all of which are in one direction; the other of an equally numerous series of intermitting small currents which are alternately in opposite directions. The lamps for those two cases differ from each other in principles, the arrangement which is needful for the one will fail for the other.

The power of the proposed batteries - those proposed trial adjustment - the strength & adjustment of the Electro magnet M.N. - of their springs and their wires - the fixture & adjustment of the various parts of the apparatus in one whole are not even indicated or adverted to. I do not expect that the lamp if carried to completion would be cheap simple & steady in action or present any advantages over those already perfected by Watson Duboscq Holmes Serrin⁴ and the many others who have worked at the subject or even equal them⁵. Further I conclude that until the use of Electricity in a lighthouse is justified in other respects than those touching the lamp only no new lamp has any claim to the attention of the Trinity House⁶[.]

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

Geo Herbert Esqr | &c &c &c

Trinity House | I return the drawing as desired MF.