All these centuries it has stood strong on its great reef, and has served to guide the shipping of Bordeau and the Languedoc Canal, and all that part of the Bay of Biscay; and it promises, in all human probability, to show its steadfast light for centuries to come. Corduan is stoutly built in four stories, each of a different order of architecture, highly ornamented and adorned with the busts of the Kings of France, and of the heathen divinities. The first story contains the store-rooms, the second, the so-called King's apartments, the third a chapel, and the fourth the dome or lower lantern. The tower completed is 197 feet high. When this splendid structure was completed no better method for illuminating was known than by burning billets of oak wood in a chauffer in the upper lantern; and it was considered a great matter when a rude reflector in the form of an inverted cone was suspended above the flame to prevent the light from escaping upward. It is not known, in fact, that any more effective mode of lighting was employed until 1760, not much more than one hundred years ago; and then the radiance was not especially brilliant as it would seem to us. At that time Smeaton the engineer began to use wax candles at the Eddystone Light-house, which soon degenerated to tallow dips, probably on account of the expense, and they must have given the keeper abundance of occupation in the way of snuffing and replenishing. In 1789 a French scientist, M. Lenoir, made an epoch in the history of Light-houses, and in the progress of civilization as well, when he introduced an improvement in the way of lighting up the _Tour de Corduan_; for, of course, the comparative safety in coast navigation attained to by means of our modern Light-house system is of the first consequence in commerce and international communication, which means the spread of science, enlightenment and religion throughout the world. M. Lenoir placed Argand lamps with parabolic mirrors or reflectors in the lantern, which is, as it appears, a glass room on the summit of the tower entered by a trap-door at the head of a spiral staircase. Such a great change having been brought about, men of science have not rested content, but have gone on making one advance after another. In 1820 the famous diaptric instruments of Mr. Fresnel were placed in Corduan on trial, and proved such a grand success that, gradually, they have been universally adopted. The wonderful lens which you saw at the Centennial belongs to a diaptric refracting light of the first order, and oil lamps constructed on the Fresnel principle, and, placed with lenses of different orders, according to the Light-house they are used for, serve an admirable purpose. Lard is found to be the best illuminator, as a general thing, for the light it casts through lenses of the first order reaches as far out to sea as it is possible for any light to be seen on account of the convexity of the earth.