DRYING MACHINES. 481 DBY ROT. which are then broujiht as dose as possible to- gether, anil one roller is turned by a liandle; the other, being tree to revolve, turns also as the clothes pass between them — the moisture in this case being extraete<l by pressure as in the com- mon process of 'wringing.' In the various branches of textile ami paper manufacture, dry- ing apparatus adapted to the particular industry is used, and is described in the separate articles on the-e subjects. DRYING OILS. See Oils. DRY MURRAIN mur'rfu. See Texas Fevki;. DRYNESS. A technical term in painting, used iM iiidicale a style in which the drawing is hard, aiiatihir. and formal, and the color de- ficient in harmony and mellowness. It is op- posed to a free method of drawing, and to the unctuous manipulation of pigment. Dryness indicates a defect that seems as much the result of the personal temperament of the painter as of any misuse of the materials which are the resources of his art. The earlier works of the Italian and of the Flemish schools, and their imitators, the pre-Raphaelites. have been criti- cised for this defect, but the fault is by no means confined to the old masters. DRYOPE, dri'6-pe (Lat.. from Gk. Spv6jrri). The daughter of Dryops, a King of Thessaly. who was the reputed ancestor of a people called Dryopes. She was the mother of a son by Apollo, who visited her in the form of a tortoise. She was finally carried off by the wood-nj-mphs and changed into a poplar. DRY'OPHIS. See Laxgaha and Whip-Snake. DRY PILE. A voltaic pile or batterj- con- sisting of a number of disks of paper covered with zine foil on one side and gijt or black oxide of manganese on the other. Various modifica- tions of the above form are also known by the same name. Following the invention of Volta (see Voltaic Cell ob B.ttert), Behreiis, in 1805, constructed a pile in which paper was used instead of moistened cloth, in consequence of Thich it was called a dry pile. The term dry pile is really a misnomer, as the pile is inactive unless the paper contains a certain amount of moisture. Behrens's construction was modified and improved by Zamboni. by whose name the dry pile is often loiown. In this apparatus the pile was made of so-called silver paper and paper which had been rubbed with manganese peroxide. The couples were made of small disks of the paper so treated, placed together with their coated sides outward, and these were piled up to the number of a thousand or more, each couple or ])air facing in the same direction. The entire pile was then firmly pressed into a glass tube varnished with shellae, and finally covered on the ends with brass caps. These have been made with as many as 20,000 pairs of disks and capable of charging a thin I.eyden jar of .3oO square centimeters surface in ten minutes to such an extent that its discharge melted 2.5 centi- meters of platinum wire of .05 millimeters diame- ter. The drv- pile was employed b,v Belirens and Bohnenberger in the construction of a very deli- cate gold-leaf electroscope, commonly known by the latter's name. For this purpose the dry pile was constructed in two columns connected togeth- er below, so that the poles were at the upper ends. Between these poles a single gold leaf was sus- pended. As one pole is positive and the other negative, a verj' slight charge given to the gold leaf is suilicient to make it move toward one of the poles of the dry jiile. The dry pile has also been ajiplied to the construction of a "perpetual ii'Otion" electric pendulum, in which case it is divided into two columns, in the same way as in the electroscope just described, and between them a very light i)enduUun rod is balanced on knife-edges. On the up])er end of the rod is a light metal ring which oscillates between the two poles. The penduliuu inclines first to one side and the ring touches one pole, at which it is charged. The pendulum is then repelled and carries it to the opposite pole, where the charge is neutralized, and it receives a eliargc of the opposite polarity, which reverses its motion. This action is repeated indefinitely. Such a pendulum has been in continuous motion in the University of Innsbruck since 1823. The period of its oscillation varies slightly with the humidity of the atmosphere. The energy expended is ex- ceedingly minute, as no pile can generate a sensible current except by a corresponding con- sumption of its materials in the shape of chemical action. See Voltaic Cell or Battery. DRY POINT, or DRY-POINT WORK. The art and process of encraviiig on metal with a needle or other sharp point which scratches the surface. It differs essentially from line-engrav- ing in that none of the metal is cut away : and from etching in the absence of acid which cor- rodes the metal. The scratches of the point cause a certain turning tip or accumulation of the metal, in rough projection, beside the serateli or cut: this roughness is called the bur, or burr, and has much to do w'ith the peculiar effect of the prints on paper. Dry-point work is often used upon a plate which has been previously etched, because it cafi be applied without re- coating the plate with the varnish and then using the mordant. (See Lixe-Exgravixg.) The term dry point is also applied to the sharp instrument with which the plate is scratched. See BiRix. DRY ROT. A popular name for the decay of timber after it has been seasoned. Dry rot is usually slow in its action, though under some circumstances it may be rapid and destructive, ruining edifices and causing serious accidents. Dry rot is caused by the fungus ilerulius lachry- mans. Somewhat similar effects are due to cer- tain species of Polyporus. The disease is quite common in timber that is exposed to moisture, as the ends of joists set in damp walls, wains- coting about sinks, etc. The timber is ultimately reduced to powder within a thin surface .shell of sound wood. Although called dry rot. moisture is essential for the development of the fungus that causes it. The spores germinate and send their mycelium through the wood in all direc- tions, attacking and destroying the wood fibres. At first the fungus appears as a thin white film which gradually thickens at the centre and changes to a rusty browii color. A kind of timlier known as red strijieil shows the beginning of dry rot. Perfectly sound timber may become infested by spores gaining entrance through cracks in the ends of logs, which, when wet, swell up. If the moisture be constant, the drj'
