LIGHTFOOT, The Rev. JOSEPH BARBER, D.D., bishop of Durham, a distinguished English scholar and theologian. Born at Liverpool in 1828, he was educated at Cam bridge, obtained numerous distinctions there, and in 1857 became a tutor of Trinity. In 18611e was made professor of divinity; in 1871, canon of St. Paul's; and in 1879, bishop of Durham. His best known works are revised texts, with introduction and notes, of St. Paul's epistles to the Galatians (4th ed. 1874), Philippians (3d ed. 1873), and Colossians (1875), and of Clement's epistles to the Corinthians. He has also written on the Gnostic heresies and on the canon of Scripture.
a building on some conspicuous point of the sea-shore, island or rock, from which a light is exhibited at night as a guide to mariners. The light-houses of the United Kin,gdom now number, with harbor-lights, upwards of 500 stations, and include some of the finest specimens of engineerimr, such RS Smeaton's Eddystone, Robert Stevenson's Bell rock, Alan Stevenson's .Skerryvore, and James Walker's Bishop rock. More recently, somewhat similar structures have been erected on the Wolf rock in the English channel by Mr. Douglass, and on the Duheartach rock, Argyleshire, and on the Chickens, off the isle of Man, by Messrs. D. & T. Stevenson. As information will be found under their respective heads regarding some of these interesting works, we shall restrict ourselves in the following short memoir to the most approved means of producincr a powerful light for the use of the mariner.
Catoptrie or Reflecting Sysrem.—All of those rays of light proceeding from the focus ,of paraboloid which fall upon its surface are reflected parallel to the axis so as to form It solid beam of light. When a series of such reflectors are arranged close to each other round a cylinder in light-house, they illuminate constantly, though not with equal intensity, the whole horizon. As the property of the parabolic reflector is to collect the rays incident npon its surface into .0I1C beam of parallel rays, it wonld be absolutely impossible, were the flame from which the rays proceed a mathematical point, to pro
zon may thus be illuminated by reflectors.
If, for the purpose of distinction, it is desired to show a revolving light, then several of those reflectors are placed with their axes parallel to each other on each of the faces of a four-sided frame, which is made to revolve. In such a case, the mariner secs a light only at those times when one of the faces of the frame is directed towards him, but at other times he is left in darkness. The rotation of the frame upon its axis thus produces to his eye a succession of light and dark intervals, which enables him to dis tinguish it from the fixed light which is constantly in view in every azimuth. The dis tinction of a red light is produced by using a chimney of red instead of white glass for each burner. The flashing or scintillating light, giving, by rapid revolutions of the frame, flashes once every five seconds, which is one of the most striking of all the dis tinctions, was first introduced by the late Mr. Robert Stevenson, the engineer of the northern light-houses, in 1822, at Rhinus of Islay, in Argyleshire. The same engineer also introduced what has been called the intemultent light, by which a stationary frame with reflectors is instantaneously eclipsed, and is again as suddenly revealed to view by the vertical movement of opaque cylinders in front of the reflectors. The intermittent is distinguished from the revolving light, which also appears and disappears successively to the view, by the suddenness of the eclipses and of the reappearances, whereas in all revolving lights there is a gradual waxing anci waning of the light. The late Mr. Wilson. introduced at Troon harbor an intermittent light which was produced by a beautifully simple contrivance for suddenly lowering and raising a gas-flame. Mr. Robert Louis Stevenson has proposed an intermittent light of unequal periods by causing unequal sectors of a spherical mirror to revolve between the flame and a fixed dioptric appara tus (such as that shown in fig. 1). The power of the light is increased by the action of the spherical mirror, which also acts as a mask in the opposite azimuths. The number of distinctive light-house characteristics has not yet been exhausted in practice, for various other distinctions ma3- be produced by combination of those already in use; as, for example, revolving, flashing, or intermittent lights might be made uot only red and white alternately, but two red or white, with one -white or red. Similar combinations could of course be employed where two lights are shown from the same or from sep arate towers.