WAT 



WEB 



third, five for the fourth, three for the 

 fifth, and one for the sixth ; it vill be 

 found that the surface of the water will 

 descend regularly through each of those 

 divisions in an hour. 



WATER-GILDING. The process of 

 gilding by the application of an amalgam 

 of gold to the surface of metals; the 

 mercury of the amalgam is driven off by 

 heat, and a thin coating of gold remains. 



WATER-SPOUT. A meteorological 

 phenomenon of the same class probably 

 as the whirlwinds which raise pillars of 

 sand in the deserts of Africa. A column 

 of water is observed to descend from a 

 cloud, until it meets a column rising 

 from the sea ; the two unite, and often 

 move with great rapidity, until they 

 meet with some opposing wind, or other 

 cause, which destroys them. 



WATER-TIGHT. That degree of 

 closeness of a vessel or tube, which pre- 

 vents the ingress or the egress of water. 



WATER-WHEEL. A machine in- 

 vented by Segner for employing the pres- 

 sure of water in the production of a rota- 

 tory motion. It consists of a hollow cylin- 

 der, turning upon a vertical axis, and 

 kept full of water. At its base are seve- 

 ral pipes for the issue of the water ; the 

 apertures of the pipes are all in one di- 

 rection, tangential to the circumference 

 of the cylinder. The pressure produced 

 against the sides of the pipes produces 

 a motion of the cylinder in an opposite 

 direction. The motion ceases if the 

 water flow in an opposite direction from 

 an equal number of pipes. 



WATERS, MINERAL. A term con- 

 ventionally applied to v^aters distin- 

 guished from all others by their peculiar 

 ingredients or supposed medicinal effects. 



1. Chalybeate waters contain iron, most 

 commonly in the state of carbonate dis- 

 solved in carbonic acid, the proportion 

 rarely exceeding one grain in a pound of 

 ■water. They occur at Brighton, Chelten- 

 ham, Bath, &c. 



2. Sulphureous waters contain sul- 

 phuretted hydrogen gas, in a proportion 

 not exceeding that of air in spring water, 

 and no oxygen. They are recognized by 

 thieir peculiar odour, and by their blacken- 

 ing silver and salts of lead. They occur 

 at Harrowgate, Aix-la-Chapelle, &c. 



3. Saline waters contain various salts 

 of lime and magnesia, and generally 

 common salt; their density is always 

 considerably higher than that of pure 

 water. They occur at Leamington, Chel- 

 tenham, Seidlitz, &c. Sea-water con- 



373 ' 



tains 3^ per cent, of saline matter, and 

 has a density of 1.0274. 



WAVE. The simplest idea of a wave 

 may be obtained by observing the curve 

 produced by a cord when its equilibrium 

 has been disturbed. The portion of the 

 curve which rises above the original posi- 

 tion of the cord, is the elevation of the 

 wave ; that which falls below the original 

 position of the cord, is the depression of 

 the wave. These movements occur in 

 solid, in liquid, and in aeriform bodies. 

 See Undulation. 



WA'VELLITE. Phosphate of alu- 

 mina; a mineral sibstance which was 

 originally mistaken for a hydrate of pure 

 alumina, and hence called hydrargyllite. 

 It occurs in Devonshire, where it was 

 first found by Dr. Wavell ; at Amberg in 

 Bavaria, where it is called lasionite; in 

 Greeenland, &c. 



WAVY. Undulated. This term is 

 applied, in botanical language, to a leaf, 

 which has an uneven, alternately convex 

 and concave margin, as in holly. In 

 entomology, it is applied to an insect 

 which has the margin of its body marked 

 by a series of arched incisions. 



WEALD CLAY. The upper portion 

 of the Wealden Formation, consisting of 

 beds of clay, sandstone, calcareous sand- 

 stone, conglomerate, limestone, and iron- 

 stone. The term weald has been given 

 to a valley, or tract of country, lying 

 between the North and the South Downs 

 of Kent and Sussex. 



WEALDEN ROCKS {wald, German, 

 a wood). A series of rocks which imme- 

 diately cover the upper oolites without 

 any breach of continuity. They are 

 essentially of fresh-water origin, and in 

 this respect they bear the same relation 

 to our older secondary rocks which the 

 old carboniferous system bears to the 

 inferior palaeozoic groups. The lowest 

 part of this formation is the Purbeck 

 Limestone; above this is the Hastings 

 Sand ; the uppermost portion is the 

 Weald Clay. 



WEATHER-GLASS. The popular 

 name for the barometer, the variations 

 of this instrument being commonly sup- 

 posed to indicate approaching changes in 

 the state of the weather. In former 

 times, the same appellation was given to 

 the thermometer. 



WE'BSTERITE. Aluminite. Hy- 

 drous subsulphate of alumina, found in 

 Sussex and at Halle in Magdeburg, and 

 formerly mistaken for pure alumina, also 

 for hydrate of alumina with mechanically 



