“In the centre of the floor stands the revolving machinery enclosed in a heavy metal case, upon which the huge lens, with its supporting carriage, revolves. The lens itself--a marvel of the glassmaker’s art--is the production of a French firm. Imagine a huge saucer, twelve feet in diameter, composed of twenty concentric prisms of purest glass, each with a diameter almost as much as a man may enclose with both hands, terminating centrally in a sixteen inch plano-convex lens or bull’s-eye. Suppose the rim of this saucer to the extent of four prisms be turned sharply inwards, the whole set vertically on edge--convexity outwards--and a vertical section--in which the bull’s-eye and three adjoining prisms are alone intact--projected a foot further forward, one may gain some idea of that particular portion of the lens allotted to the red flash, the colour of which is attained by means of sheets of red glass attached inside the central section and on the outside of the adjoining wings. On the opposite side of the lens, and in a line with the central red section, is a similar section--minus the adjoining wings and the red media--through which the white flash is transmitted. Both flashes are intended to equal each other in intensity, which accounts for the much smaller portion of the lens allotted to the white. A belt of horizontal prisms, three feet wide, connects the wings of the red section with the white on either side, and reflects the rays of light equally to both sections. Stooping underneath this belt, access is obtained to a fixed circular platform in the interior of the lens. In the centre of this platform, upon an iron pedestal, is placed the source of illumination, a large six-wick lamp. Between this platform and the top of the machine case, the circular carriage upon which the superstructure of the lens is erected revolves upon twelve five-inch steel rollers travelling upon a circular metal pathway. Attached to the under side of this carriage is a heavy gun-metal ring, six feet in diameter, toothed on its inner circumference, which engages with a horizontal pinion wheel rising from the corner of the machine case, and through which the driving power is transmitted. The machine--an exaggerated form of clockwork--is driven by a weight of 400 lbs. travelling in the centre of the spiral stair on the first flat. The speed of the machine is regulated by adjustable fans; and a speed indicator, furnished with an alarm bell, intimates the periods of winding--an operation necessitating two minutes’ stiff winding every half-hour. The entire lens, with its supporting carriage, is estimated to weigh about six tons. The lamp, as I have already stated, is placed upon an iron pedestal in the centre of the platform, or service table, as it is called, in the interior of the lens. It is fitted with what is known as the stepped Doty burner, and carries six concentric wicks, each slightly elevated above the other towards the centre. The burner