Achilles Tatius (a-kil′ēz tā′shi-us), a Greek romance writer of the fifth century A.D., belonging to Alexandria; wrote a love story in 8 books called Leucippē and Cleitophon.
Achimenes (a-kim′e-nēz), a genus of tropical American plants, with scaly underground tubers, nat. ord. Gesneraceæ, now cultivated in European greenhouses on account of their white, blue, and red flowers.
Achlamydeous (ak-la-mid′i-us), in botany, wanting the floral envelopes, that is, having neither calyx nor corolla, as the willow.
Achor (ā′kor), a disease of infants, in which the head, the face, and often the neck and breast become incrusted with thin, yellowish or greenish scabs, arising from minute, whitish pustules, which discharge a viscid fluid.
Achromat′ic (Gr. a, priv., and chrōma, chrōmatos, colour), in optics, transmitting colourless light, that is, not decomposed into the primary colours, though having passed through a refracting medium. A single convex lens does not give an image free from the prismatic colours, because the rays of different colour making up white light are not equally refrangible, and thus do not all come to a focus together, the violet, for instance, being nearest the lens, the red farthest off. If such a lens of crown-glass, however, is combined with a concave lens of flint-glass—the curvatures of both being properly adjusted—as the two materials have somewhat different optical properties, the latter will neutralize the chromatic aberration of the former, and a satisfactory image will be produced. Telescopes, microscopes, &c., in which the glasses are thus composed are called achromatic.
Acid (Lat. acidus, sour), a name applied to a number of compounds, having more or less the qualities of vinegar (itself a diluted form of acetic acid). Their general properties are sour taste, the power of changing vegetable blues into reds, of evolving hydrogen in presence of magnesium, of decomposing chalk with effervescence, and of being in various degrees neutralized by alkalies. An acid has been defined as a compound of hydrogen, the whole or a part of which is replaceable by a metal when this is presented in the form of a hydroxide; being monobasic, dibasic, or tribasic, according to the number of replaceable hydrogen atoms in a molecule. See Chemistry.
Acierage (ā′sē-ėr-āj), (Fr. acier, steel), a process by which an engraved copper-plate or an electrotype from an engraved plate of steel or copper has a film of iron deposited over its surface by electricity in order to protect the engraving from wear in printing. By this means an electrotype of a fine engraving, which, if printed directly from the copper, would not yield 500 good impressions, can be made to yield 3000 or more; and when the film of iron becomes so worn as to reveal any part of the copper, it may be removed and a fresh coating deposited so that 20,000 good impressions may be got.
Acipenser (as-i-pen′sėr), the genus of cartilaginous ganoid fishes to which the sturgeon belongs.
Aci Reale (ä′chē rā-ä′lā), a seaport of Sicily, north-east of Catania, a well-built town, with a trade in corn, wine, fruit, &c. Pop. 35,587.
A′cis, according to Ovid, a beautiful shepherd of Sicily, loved by Galatea, and crushed to death by his rival the Cyclops Polyphemus. His blood, flowing from beneath the rock which crushed him, was changed into a river bearing his name, and renowned for the coldness of its water. It has been identified as the Fiume di Jaci.