Faraday to Peter Henry Berthon   2 January 1863

Royal Institution, 2 January 1863.

Sir,

I wrote you so recently¹ in reference to the various reports of the Dungeness Electric Light for the month of November, that I think I may make the observations short in respect of the more extensive reports which I now return to you, extending from June to last month.

Dungeness.- The report of the engineer says that both wheels and both engines worked during every night; that the light went out of itself twice in June, twice in July, once in August, five times in September, five times in October, three times in November; that generally the extinction was only for a moment, but that once in September it was out for two minutes, also that in November the extinction was once for 15 seconds, and another time for 30 seconds; and that all the three times in that month Chaplin² was the assistant in charge, and was away from the lamp on two of the occasions. The reports show also the longest interval in each night during which the lamp could be left untouched. This on six nights was 50, 45, 45, 45, 40, 30 minutes, on each of which nights the intervals must have been these or less; and it shows how close the attention on the electric lamp must be, and how greatly the danger from neglect is increased. The month of November also illustrates the deterioration of the light consequent upon the used condition of the commutator, occasioned by the passage of the electric discharge. There appears to be no difficulty in retaining the light exactly in its right place.

South Foreland High Light.- The Electric Light is constant, i.e., there is no note of extinctions. Columns 1 and 2 are not at first so favourable for the Electric Light as reports from other places; but from the beginning of September improvement occurs. I am not sure whether in column 2 the Dungeness or the Grisnez light is intended to be referred to as the brightest. The new form of table will make the comparisons more clear.

South Foreland Low Light.- Nearly as the last. Improves as regards Dungeness as the report proceeds. No failure of the Electric Light. Dungeness and Grisnez are very nearly equal in intensity, which tends to confirm the results drawn in my last letter.

Varne Light Ship.- The Dungeness light never out. The Grisnez is recorded as having stopped in its revolution once for 12 minutes. The Electric Light was almost always the brightest of any in sight. The Grisnez was rarely visible when the Electric Light was not also visible, and the Electric Light was often visible when Grisnez was not. I shall be glad to have the new reflecting ball observations.

Wellington Pilot Cutter.- The bearing of the vessel was usually more or less east; the distance generally within nine miles, though sometimes up to 14 or 15 miles. It reports the Electric Light as always superior to the others in sight. It was once invisible at the distance of only two miles, but there was a fog, and the fact shows how fog can hide a light. There were no extinctions of the light, nor any false appearances.

Lord Warden Pilot Cutter.- Generally favourable, and like the others no reports, but from the 3rd to the 9th November reports the light as wavering and unsteady, and three times it partook of the character of a revolving light. The observations of the 10th and 11th November are repeated in the report, and are not consistent, as to the brightness (see column 1).

Princess Pilot Cutter.- Generally as the other sea reports, but more constantly favourable as to brightness. Nevertheless, at the end of the 14th November, or rather morning of the 15th at 6.30, the light was out for about two minutes.

Queen’s Pilot Cutter.- Generally as the other sea reports, but more constantly favourable. The Dungeness Light was equal to the Grisnez when the cutter was 10, 11, 12, 14 miles off towards the east or north-east³.

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

P.H. Berthon, Esq.