FOCUS 163 FOU. western front under a single command, with General Foch as supreme director of operations. Henceforward, the co- ordination of the Allies equalled that of the Germans, and the defeat of the latter was assured. In the following October Marshal Foch, who still remembered vividly the experiences of the French during the Franco-Prussian War, had the supreme honor of receiving the Ger- man delegation which brought the sur- render of the Central Empires into his hands. FOCUS, in ordinary language, any place from which an influence emanates, or where that influence exists in very concentrated form. In optics, a point at which the rays of light refracted from a convex lens, or reflected from a con- cave mirror, are most concentrated; a point in which such rays meet, or tend to meet; if produced either backward or forward. In conic sections: (1) Singular (of a parabola) : A point so situated that if from it there be drawn a line to any point in the curve, and another from the latter perpendicular to a straight line given in position, these two straight lines will always be equal to one an- other. (2) Plural: (a) Of an ellipse: Two points so situated that if two straight lines be drawn from them to any point in the curve, the sum of these straight lines will always be the same, (b) Of a hyperbola: Two points so situated that if two straight lines be drawn from them to any point in the curve, the excess of the straight line drawn to one of the points above the other will always be the same. In astronomy, the term foci is often used in connection vnth the orbit of the earth, which is an ellipse, with the sun in one of the foci. In acoustics, the point of convergence of sound rays, these fol- lowing the same laws as those of light and heat. Acoustic focus: The focus of sound rays. Calorific focus: The focus of heat rays. Conjugate foci: In optics, two foci so situated that, if rays of light diverging from one strike a concave mirror, they will be reflected and meet in the other. Luminous focus: In optics, the focus of light rays. Principal focus: In optics, the focus of parallel rays strik- ing a concave mirror. Vertical focus : In optics, a radiant point behind a mirror, from which rays may be held to diverge more and more, and in which, looking at them now as coming from the opposite direction, and consequently as conver- gent, they would tend to meet. Magnetic foci: The two points on the earth's sur- face where the magnetic intensity is greatest; they nearly coincide in position with the magnetic poles. FOG. a very thick mist; small hollorw vesicles of water suspended in the air, but so low as to be but a short distance from the earth in place of rising high above it and becoming so illuminated by the sun as to constitute clouds of varied hue. Fogs often arise when the air above warm, moist soil is colder than the soil itself. The hot vapors from the ground are then condensed by coming in contact with the colder air above, as the warm steam of a kettle is by the comparatively cold air of a room. But no fog arises till the cold air has absorbed vapor enough to bring it to the point of saturation. Fogs often hang over rivers. Their cause is the condensation by contact with the cold water, Of the vapor in a hot and moist air current passing over the river. FOGAZZARO. ANTONIO (fo-gats- ar'6), an Italian poet; born in Vicenza, Italy, in 1842. He first came into notice with "Miranda," a story in verse (1874), and added greatly to his reputation as a poet with "Valsonda," a volume of lyrics (1876). He was author of several novels which were received with marked favor, among them, "Master Chicco's Fiasco" (1885) ; "Daniel Cortis" (1887) ; "The Poet's Mystery" (1888); "The Saint" (1905); "Leila" (1910). FOGGIA, a city of southern Italy, capital of the province of the same name, in the center of the great Apulian plain, 46 miles E. by S. of Campo Basso. It is well built, most of the houses being re- constructed since an earthquake, which happened in 1732. It has large store- houses for keeping corn, and is the place where the flocks that feed on the great plain of Apulia are registered. Pop. about 79,000. FOGO, FUEGO. or ST. PHILIP, one of the Cape Verde Islands, in the At- lantic Ocean, and the highest of the group, being 9,760 feet above sea-level, and presenting the appearance of one single mountain, though, on the sides, there are deep valleys; area, 40 miles in circumference; pop. estimated, 16,000. It has no rivers, and a scarcity of fresh water prevails, yet it is one of the most fertile islands of the archipelago, pro- ducing excellent maize and fruits. Chief town, Nostra Senhora da Luz. Also the name of a port of entry, capital of Fogo Island, Newfoundland. FOHR (fer), an island in the North Sea, ofl' the W. coast of Schleswig; area, 28 square miles; population mostly Frisians engaged in fishing, the capture of wild fowl, and agriculture. FOIL, in fencing, a rod of steel, repre- senting a sword, with a handle or hilt at
