VELVET 179 VENDEE, LA he really completes four miles, or that he walks for one hour, but only that he would do so were he to keep up that speed for the time named. In fact, speed is an instantaneous property of the mov- ing point. Again since at every instant the moving point must be moving in a definite direction, as well as with a de- finite speed, it follows that velocity also is an instantaneous property. If it does not change from instant to instant, the velocity is constant, and the point moves in a straight line with constant speed. If the point moves in any other than a straight line, the velocity will be variable even although the speed should remain constant ; and the most general change of velocity involves both change of direction and change of speed. Velocity is in fact a vector quantity, and may be treated mathematically as a Vector (g. v.). The rate at which velocity changes is called acceleration. When the velocity changes in direction only, as when a point moves with constant speed in a circle, there is no acceleration in the di- rection of motion — i. e., parallel to the velocity. The acceleration must there- fore be wholly normal to the velocity, and will be toward the center of the circle in the simple case of uniform circular motion. If any change of speed occurs it is due to an acceleration acting paral- lel to the velocity, and therefore tangen- tial to the path pursued by the moving point. When only a tangential accelera- tion exists, the point will move in a straight line with variable speed. A body falling vertically near the earth's sur- face gives a very good illustration of a pure tangential acceleration. VELVET, one of the most familiar of what are known as pile fabrics. It is produced by adding to the usual warp and weft threads of plain weaving an additional row of warp yarns which are woven into the ground of the cloth, and passed over wires on the surface. In the case of a loop pile the wires are simply drawn out, but for velvet or other cut pile a knife is first passed along a groove on the top of each wire to cut the pile be- fore the wire is vidthdrawn. Real velvet is made entirely of silk, but a kind is made with a silk face on a cotton basis. The name velveteen is, however, ex- tended to fabrics in which silk and cotton are mixed throughout. Some of the rich- est and most artistic of the many splen- did textiles woven on Italian looms in the 15th and 16th centuries were made, in part at least, of velvet. Similiar stuffs were also made in Spain and Flanders. Many of these were for ecclesiastical vestments, altar cloths, and the like, as well as for hangings. Plain velvets were likewise woven. The effect of a raised pattern in velvet on a plain or figured silk ground is often very beautiful. Sometimes a diaper design was formed of a long upon a short pile, called vel- vet upon velvet, and this too has a fine eflTect. Choice examples of these old vel- vet fabrics are preserved in some indus- trial art collections. Velvet is believed to have been first made in China. Mod- em velvets are largely made at Lyons and Crefeld. VENABLE, FBANCIS PEESTON, an American chemist; born in Prince Ed- ward CO., Va., Nov. 17, 1856; was grad- uated at the University of Virginia in 1879, and studied at the Universities of Bonn, Gottingen, and Berlin successively in 1879-1880, 1881, and 1889. In 1900 he was made president of the University of North Carolina and its Professor of Chemistry. His publications Include: "Manual of Qualitative Analysis" (1883); "Short History of Chemistry" a894) ; "Development of Periodic Law" (1896) ; "Inorganic Chemistry Accord- ing to Periodic Law" (with Prof. James Lewis Howe, 1898) ; "Study of the Atom" (1904). VENABLES, EDMUND, an English archaeologist; born in London, England, in 1819. He was canon of Lincoln. Cathedral from 1867, and wrote much on architecture and archaeology, among his works being "Walks Through the Streets of Lincoln," widely popular; "History of the Isle of Wight" (I860) ; "The Church of England: Its Planting, Settlement, Reformation. Renewed Life" (1886) ; "Bunyan" (1888). He died in Lincoln, March 5, 1895. VENATION, the arrangement of the veins in the leaves of plants. If a leaf has only a single midrib without branches as in many Coniferx, the vena- tion is said to be simple. The three leading types of venation are the reticu- lated, netted, or angular, found in the exogens and a few aberrant endogens; the parallel, or curved, found in all the higher endogens; and the furcate, or forked, characteristic of ferns. Lindley made 10 divisions: veinless, equal-veined, straight- veined, curve-veined, netted, ribbed, falsely ribbed, radiating, feather- veined, and hidden-veined. Professors McCosh and Dickie considered that they had traced a connection between the ramifications of plants and their vena- tion. VENDEE (vowgr-da'), LA, a maritime department of western France; bounded on the W. by the Bay of Biscay, on the N. by Loire-Inferieure, and on the S. by Charente-Inf erieure ; area, 2,690
