It may be well to describe the apparatus. There are 120 permanent magnets, weighing about 50 lbs. each, ranged on the periphery of two large wheels. A steam-engine of about three-horse power causes a series of 180 soft iron cores, surrounded by coils of wire, to rotate past the magnets. This calls the power into action, and the small streams of electricity are all collected together, and by what is called a "commutator" the alternative positive and negative currents are brought into one direction. The whole power is then conveyed by a thick wire from the engine-house to the lighthouse tower, and up into the centre of the glass apparatus. There it passes between two charcoal points, and produces an intensely brilliant continuous spark. At sunset the machine is started, making about 100 revolutions per minute; and the attendant has only to draw two bolts in the lamp, when the power thus spun in the engine-room bursts into light of full intensity. The "lamp" regulates itself, so as to keep the points always at a proper distance apart, and continues to burn, needing little or no attention for three hours and a half, when, the charcoals being consumed, the lamp must be changed, but this is done without extinguishing the light. Again there were inspections, and reports from pilots and other observers, and Faraday propounded lists of questions to the engineer about bolts and screws and donkey-engines, while he estimated that at the Varne light-ship, about equidistant from Cape Grisnez and Dungeness, the maximum effect of the revolving French light was equalled by the constant gleam from the English tower. But delays again ensued till intelligent keepers could be found and properly instructed; but on the 6th June, 1862, Faraday's own light, the baby grown into a giant, shone permanently on the coast of Britain. France, too, was alert. Berlioz's machine, which was displayed at the International Exhibition in London, and which was also examined by Faraday, was approved by the French Government, and was soon illuminating the double lighthouse near Havre. These magneto-electric lights on either side of the Channel have stood the test of years; and during the last two years there has shone another still more beautiful one at Souter Point, near Tynemouth; while the narrow strait between England and France is now guarded by these "sentinels of peaceful progress," for the revolving light at Grisnez has been lately illuminated on this principle, and on the 1st of January, 1872, the two lights of the South Foreland flashed forth with the electric flame.[30]