skepticism Philosophical doubting of knowledge claims in various areas. From ancient to modern times, skeptics have challenged accepted views in metaphysics, science, morals, and religion. Pyrrhon of Elis (c. 360-272 bc) sought mental peace by avoiding commitment to any par¬ ticular view; his approach gave rise in the 1st century bc to Pyrrhonism, proponents of which sought to achieve suspension of judgment by sys¬ tematically opposing various knowledge claims. One of its later leaders, Sextus Empiricus (2nd or 3rd century ad), strove for a state of imper¬ turbability. Modern skeptical philosophers include Michel de Montaigne, Pierre Bayle, and David Hume.
ski jumping Skiing event in which contestants ski down a steep ramp curved upward at the end and launch themselves into the air for distance. Using a crouch position, skiers can achieve ramp speeds of 75 mi (120 km) per hour. After takeoff, they lean far forward from the ankles with knees straight and skis held open at the tips to form a V, a position that minimizes wind resistance and maximizes lift. Scoring is based partly on distance and partly on form.
skiing Sport and mode of transportation involving moving over snow on a pair of long flat runners (skis) attached to shoes or boots. Skiing was born in northern Europe; the oldest skis, found in Russia, are some 6,000 years old. The earliest skis were often short and broad. The first written references to skiing come from the Han dynasty (206 bc-ad 220) and describe skiing in northern China. Skiing was used in warfare in Scan¬ dinavia from the 13th century or earlier to the 20th century. The earliest mode of skiing developed into the sport now called cross-country skiing. Competitive cross-country skiing began in Norway in the 1840s and had reached California by the 1860s. Improvements on primitive bindings c. 1860 led to greater popularity of recreational skiing. Ski-jumping compe¬ titions date from the 1870s. Downhill skiing was limited by the need to climb the hill before or after skiing down; the building of ski lifts began in the 1930s. Skis were originally made of a single piece of wood, usu¬ ally hickory; laminated construction began in the 1930s, plastic running surfaces were introduced in the 1950s, and no wood has been used in the construction of downhill skis for several decades. The business of skiing began its serious growth in the 1930s and became explosive in the 1950s and ’60s; huge resorts now dot the Austrian, Swiss, and Italian Alps, the Rocky Mountains, and other mountainous regions. See also Alpine skiing.
skimmer Any of three species (family Rynchopidae) of waterbirds hav¬ ing a red bladelike bill, with the lower mandible longer than the upper. Skimmers live chiefly in estuaries and along wide rivers in warm regions. At twilight, they skim calm, shallow water with the open bill tip sub¬ merged; when a fish or crustacean is hit, the upper mandible snaps down. Skimmers are dark above with white underparts, face, and forehead, red legs, and black wings. The American black skimmer ( Rynchops nigra ) grows to 20 in. (50 cm) long.
skin Surface covering of the body that protects it and receives external sensory stimuli, consisting of an epidermis over a thicker dermis. The epidermis contains cells involved in immune defenses, sensory receptors, pigment cells, and KERATiN-producing cells. The last harden and migrate to the surface to form a dead, relatively dry outer layer of horny tissue that constantly sloughs away. The dermis contains sensory nerves and blood vessels within connective tissue. Collagen and elastin fibres give skin its tough, elastic quality. Cells scattered through it produce its components and take part in immune and other skin responses. A fat layer under the dermis provides nutritional storage, cushioning, and insulation. Skin dis¬ orders range from dermatitis and acne to skin cancer. Changes in skin colour (e.g., jaundice) or texture may be clues to systemic disorders. See also dermatology; hair; integument; nail; perspiration; sebaceous gland; sweat gland. See illustration on opposite page.
© 2006 Encyclopaedia Britannica, Inc.
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A section through the skin. The tough, dead cells of the outer epidermal surface (corneal layer) serve as a physical barrier and are continually replaced by cells produced in the basal layer. The thick supportive layer of dermis contains nerve endings, blood vessels, sweat glands, hair follicles, and oil glands. The hair follicle encloses the root of the hair. Oil glands associated with hair follicles secrete an oily substance (sebum) which lubricates the skin surface. The watery secretions of the tubular sweat glands are released onto the skin's surface through small pores. A layer of fat cells lies below the dermis.
© MERRIAM-WEBSTER INC.
skin cancer Malignant tumour of the skin, including some of the most common human cancers. Though recognizable at an early stage, it has a significant death rate. Light-skinned people have the highest risk but can reduce it by limiting exposure to sunlight and to ionizing radiation. The most common types arise in the epidermis (outer skin layer) and have become more frequent with the thinning of the atmosphere’s ozone layer. The most serious form is melanoma, which is frequently fatal if not treated early with surgery. Cancers arising from the dermis are rare; the best- known is Kaposi sarcoma.
skinhead Member of an international youth subculture characterized by hair and dress styles evoking aggression and physical toughness. Typi¬ cal skinhead style includes shaved heads, combat boots, tattoos, and prominent body piercings. Skinheads first appeared in working-class areas of London in the 1960s; during the 1970s and ’80s the skinhead phenom¬ enon spread to Australia, North America, and western Europe. In many countries, skinheads are regarded as extreme right-wing nationalists who espouse anti-Semitic and other racist views and engage in violent attacks on immigrants and racial minorities. This characterization, however, does not apply to all members of the subculture.
skink Any of about 1,275 species (family Scincidae) of lizards found throughout the tropics and in temperate regions of North America. Skinks have a cylindrical body, a conical head, and a long, tapering tail. Some
species are 26 in. (66 cm) long, but most are under 8 in. (20 cm). Some have small or no limbs and sunken eardrums. Most are ground-dwellers or burrowers; some are arboreal or semiaquatic. Skinks eat insects and other small invertebrates; large species are herbivorous. Some species lay eggs; others bear live young.
Striped broad-headed skink (Eumeces laticeps)
JOHN H. GERARD FROM THE NATIONAL AUDUBON SOCIETY COLLECTION/PHOTO RESEARCHERS
Skinner, B(urrhus) F(rederic) (b. March 20, 1904, Susquehanna, Pa., U.S.—d. Aug. 18, 1990, Cambridge, Mass.) U.S. psychologist and influential theorist of behaviourism. He received his Ph.D. from Harvard University and first achieved notice with The Behavior of Organisms (1938). In the mid-1940s he presented his “Air-Crib,” a soundproof, germ- free, air-conditioned box meant to serve as an optimal environment for the first two years of childhood. In Walden Two (1948), a controversial but popular - work, he described a utopia based on behavioral engineering. He spent most of his teaching career at Harvard (1948-74). His other works include Science and Human Behavior (1953), Verbal Behavior (1957), Beyond Freedom and Dignity (1971), and an autobiography (3 vol., 1976-83). He received the National Medal of Science in 1968.