Page:The New International Encyclopædia 1st ed. v. 20.djvu/70

* VELLORE. 46 fumerv is the leading industry. Population, in lyOl, 43,537. VELLUM. See Parchment and Vellum. VELOCITY (Lat. velocitas, from velox, swift; connected with volure. to fly), Lineak. A term used in mechanics (q.v. ) to express linear speed in a particular direction, linear speed be- ing the distance a particle goes in a vinit of time if the motion is uniform, or the distance it would go in the next unit of time if during that time its motion were not to change. A particle mov- ing northward with a speed 10 is said to have a 'velocity 10, north.' A linear velocity has evi- dently the same properties as a straight line of definite length drawn in a definite direction, viz. direction and numerical value ; therefore, a velocity is a 'vector quantity' and can be pic- tured by such a line. (See Vector.) Angular velocity is angular speed around a particular axis, angular speed being the angle rotated through by a body turning on an axis in a unit of time if the angular motion is uniform; or, if the motion is irregular, the angle which would be turned through in the next unit of time if the motion were to remain unchanged for that length of time. To express the angular velocity of a body three things are necessary: a line to coincide with the axis, this line to be pointed in such a direction as to indicate the sense of the rotation — right or left handed — and the line to have a length equal or proportional to the angular speed. A .straight line like this, of a definite length, direction and position, is called a 'rotor' or a "localized vector.' VELOCITY OF LIGHT. This quantity through the efforts of many experimenters has been determined with a high degree of precision and plays an important part in both theoretical and practical optics and astronomy. After vain attempts at direct measurements made by Gali- leo, Roemer in 1675 was able to calculate the velocity of light from observations of the eclipse of Jupiter's satellites, making the value about 102,000 miles per second. Little further was done, however, until the nineteenth century, when Fizeau, using a revolving toothed wheel to in- terrupt a beam of light, made a direct measure- ment of light which had traveled a distance of 8633 meters. This method was also employed by Cornu, who had improved apparatus constructed and used a distance of 23 kilometers. A method involving the u.se of a ra]>idly rotating mirror was employed by Foucault in 1862, and was noteworthy in that it permitted a short distance, such as could be found in a laboratory, to be used as the pathway of the l)eam. ]?y this method, whieli was im])roved by .Michelson and Xewcomb, it was possible to measure the velocity in liquids. The values obtained by various ex- perimenters are given in the following table : Kilometerfl. Foilcault, 1862 298.000 Cornu (1), 1874 ans.ijoo (2). 1878 300.400 rormi. illHCUsHcil bv I.letlng 290,990 YoilUB anil Forbes. 1880-81 301,382 MichelBon (1) 299.910 (2) 299.853 Newcorab (selected results) 299.800 (all results) '299,810 A detailed description of the methods vi'ill be found in the article LioiiT in the paragraph on Vclority of Light, to which reference should be VENABLE. made. Consult: Preston, Theory of Light (Lon- don and Xew York, 1895) ; Cornu, in lirporla of Iittcrnationul t'ongress of I'hysics (Paris. UJOO) ; and Jlichelson. "The Velocity of Light," vol. ix., Decennial Piiblicalions Unirersity of Chicago (Chicago, 1902). VELOCITY OF PROJECTILES, etc. See Ballistics. VELVET (OF. velvet, 01. veluto, It. velluto, velvet, from Lat. villus, shaggy hair, nap of cloth, tuft of hair; connected with vellus, fleece, and ultimately with Eng. ivool). A silk material, made with a single or double filling and with a double warp. The latter is disposed over metal rods so that one set of warp threads is a series of loops secured into the base of the fabric. These loops are afterwards cut and form the pile of the velvet. In figured velvet, portions of the pile are either cut closer or stamped in designs, so as to contrast with the upstanding pile. When the back is of linen or cotton, and only the pile of silk, the material is called velveteen. See Weaving. VELVET-ANT. Any one of the hymenop- terous insects of the family Mutillidfe. They resemble the true ants in general sliape, but lack the scale on the peduncle of the al)domen. They do not form communities and are more closely allied to the digger wasps than to the ants. The body is often densely clothed with hairs, hence the name 'velvet.' The hair is frequently bright- colored, in some species bright red, contrasted with black. The males only are winged and are frequently larger than the females. There are about 160 North American species, most numer- ous in the South, the largest of which is the Texivn 'horse-ant' or 'cow-killer;' it burrows in the ground and provisions its tunnels with insects. Velvet-ivnts sometimes enter bee- hives in search of bees, and there do considerable damage. Other species have been found in Europe in the nests of bumblebees, and in the United States in the nests of certain of the bur- rowing bees. It is probable that all the velvet- ants are parasitic in this way. Many of the fe- males stridulate. These insects sting viciously. VELVET-BEAN. See Cowage. VELVET-GRASS. See Soft Grass. VELVET LEAF. See Sida. VENABLE, vfm'a-b'l, Francis Preston (1850 — ). An American educator and writer on clieniistry, born near Karmville. Prince Edward County, Va. He graduated at the I'niversity of Virginia in 1879; studi (1896) ; and with .T. I^. Howe, Inorganic Chem- istry According to I'criodie Law (1898). VENABLE, William Henry (1836—). An Ameriean aiitlior and educator, born in Warren Coiuity. Ohio, and educated at the National Nor- mal School, l.elianon. Ohio. He becauu' professor of natural science in (he Chickering Classicnl and Scientific Institute, Cincinnati, Ohio, in 1862,