Faraday to Peter Henry Berthon   13 March 1863

Royal Institution, 13 March 1863.

Sir,

I have received and considered Mr. Cherry’s¹ replies to the inquiries made of him, as to the result of his experience for the ten months during which he has, as a well-instructed engineer, had charge of the Magneto-electric Light at Dungeness, being made for the time the responsible head of the whole.

Proceeding in the order of the queries submitted to him, I gather from his answers that, if the two present boilers are worked together, they can give steam enough for the two steam engines <(1)>; but that many precautions are requisite and necessary (36, 30), both below and above, to guard against the extinction of the light, and amongst them precautions as to steam-power; that if there were only two boilers, either of them should be able, under its ordinary action, to work both steam engines by itself <(3)>; but that if the boilers are such that each steam engine requires one to itself, then a third boiler is necessary <(3)>; and that as a matter of precaution, it is best to have a supernumerary boiler always cleaned, ready, and laid for lighting <(6)>.

That in the case of the steam engines there should be a third engine, exactly similar to the other two, kept ready to replace either, if needful <(7)>; and which, of course, must be so constructed as to work either magneto-electric machine; or if, as in the Dungeness case, that be not possible, to drop the use of one engine and one machine for the time. If one steam-engine at Dungeness were to fail, the other cannot work both magneto-electric machines, even if it were powerful enough <(8)>, for though it ought to do so (10, 11), it is not connected with both <(9)>, nor can be whilst they are in their present positions <(10)>.

One magneto-electric machine, such as those at Dungeness, though it would not be competent for full duty, would give a light much greater than the Argand lamps (I presume Mr. Cherry means those that are in the reflectors) <(12)>; but Mr. Cherry considers that, as a precaution <(13)>, a better plan than that of the present oil lamps and reflectors would be to have two magneto-electric machines, each competent for the whole work; one being at work, and the other standing as a supernumerary for the time, perfectly ready for work in case of accident <(14)>.

As no precaution can be too great <(18)>, an extra donkey-engine, capable of being worked by hand, would be good.

Repairs should be made at once <(19)>; bolts and screws should be cut to the Government standard <(21)>. All parts should be made to duplicate <(22)>.

The water supply at Dungeness is very good <(23)>; but it would be advisable to have a much larger tank in other situations.

In the lanthorn, if there were no precautionary arrangements, such as oil-lamps in the lanthorn, the tables for the electric lamps might be much improved <(24)>. The system works perfectly <(25)>. The lamps work better than at first (28, 29). The connecting wires remain unchanged <(26)>, and require no re-adjustment <(27)>.

Mr. Cherry thinks it is almost impossible that the light should go out permanently <(30)>, if proper precautions be taken both below and above; these precautions, I presume, include those already referred to, of duplicate boilers, steam engines, magneto-electric machines &c. But if the light should go out, that two (oil?) lamps <(30)>, properly adjusted for the foci of the two lenses should be kept ready and used together. This expedient would be of little or no use, for the foci of the optic apparatus are worked and adjusted for a point of light such as the electric discharge, and would not suit a large luminous object, such as the flame of a lamp. As shown in a former report², an oil lamp in the focus of an excellent parabolic reflector, is invisible by reason of the brightness of the Electric Light when in sight at the same time and place. Mr. Cherry thinks, however, that no substitute of any kind will be required (30, 31). If only part of the apparatus failed <(32)>, the remaining part would still give a light though not so good, but extinction would not occur.

As to help and attendance, he thinks extra help would be needed if there were any extra work <(34)>, as the fog-bell. Having a supernumerary, as at present, the case of his own illness for a few days <(35)> could be provided for.

All the precautions referred to in the 36 inquiries are necessary and requisite.

He suggests, in addition <(37)>, that an extra or fifth lamp should be provided; also, a better telegraph from the lanthorn to the engine-room; also that, where practicable, the lanthorn should be heated by the waste steam from the steam-engine; also that all flange-joints to pipes, engines, and boilers, should be made surface-joints.

I have, &c. | (signed) M. Faraday.

P.H. Berthon, Esq., Secretary.