measuring the strength or intensity of an electric current, being equivalent to the current produced by the electro-motive force of one volt in a wire having the resistance of one ohm. The name (cf. Farad, Coulomb, Watt, &c.) is derived from that of the well-known physicist, Ampère. An ampere-meter or ammeter is an instrument by which the strength of an electric current is given in amperes.

Amphib´ia, a class of vertebrate animals, which in their early life breathe by gills or branchiæ, and afterwards partly or entirely by lungs. The Frog, breathing in its tadpole state by gills and afterwards throwing off these organs and breathing entirely by lungs in its adult state, is an example of the latter phase of amphibian existence. The Proteus of the underground caves of Central Europe exemplifies forms in which the gills of early life are retained throughout life, and in which lungs are developed in addition to the gills. A second character of this group consists in the presence of two occipital 'condyles', or processes by means of which the skull articulates with the spine or vertebral column; Reptiles possessing one condyle only. The class is divided into four orders: the Ophiomorpha (or serpentiform), represented by the Blindworms, in which limbs are wanting and the body is snake-like; the Urodela or 'Tailed' Amphibians, including the Newts, Proteus, Siren, &c.; the Anoura, or Tailless Amphibia, represented by the Frogs and Toads; and the Labyrinthodontia, which includes the extinct forms known as Labyrinthodons. The term Amphibia was originally employed by Linnæus in his Systema Naturæ, and adopted by Cuvier in his Tableau Elémentaire. See Batrachia.

Amphibol´ogy, in logic, an equivocal phrase or sentence, not from the double sense of any of the words, but from its admitting a double construction, as 'The duke yet lives that Henry shall depose'.

Amphic´tyonic League (or Council), in ancient Greece, a confederation of tribes for the protection of religious worship, but which also discussed questions of international law, and matters affecting their political union. The most important was that of the twelve northern tribes which met alternately at Delphi and Thermopylæ. The tribes sent two deputies each, who assembled with great solemnity; composed the public dissensions, and the quarrels of individual cities, by force or persuasion; punished civil and criminal offences, and particularly transgressions of the law of nations, and violations of the temple of Delphi. Its calling on the States to punish the Phocians for plundering Delphi caused the Sacred Wars, 595-586, 448-447, 357-346 B.C.

Amphi´on, in Greek mythology, son of Zeus and Antiŏpē, and husband of Niŏbē. He had miraculous skill in music, being taught by Mercury, or, according to others, by Apollo. In poetic legend he is said to have availed himself of his skill when building the walls of Thebes—the stones moving and arranging themselves in proper position at the sound of his lyre. See Zethus.

Amphioxus. See Lancelet.

Amphipoda

1. Shore-jumper (Orchestia littoralis), 2. Portion showing the respiratory organs a a a.

Amphip´oda, an order of sessile-eyed malacostracan crustaceans, with feet directed partly forward and partly backward. Many species are found in springs and rivulets, others in salt water. The sand-hopper and shore-jumper are examples.

Amphip´rostyle, in architecture, said of a structure having the form of an ancient Greek or Roman oblong rectangular temple, with a prostyle or portico on each of its ends or fronts, but with no columns on its sides or flanks.

Amphisbæ´na (Gr., from amphis, both ways, and bainein, to go), a genus of serpentiform, limbless, lacertilian reptiles; body cylindrical, destitute of scales, and divided into numerous annular segments; the tail obtuse, and scarcely to be distinguished from the head, whence the belief that it moved equally well with either end foremost. There are several species, found in tropical America. They feed on ants and earthworms, and were formerly, but erroneously, deemed poisonous. In Greek mythology the

amphisbæna was a serpent believed to possess two heads.

Amphis´cii (Gr. amphi, on both sides, and skia, shadow), a term sometimes applied to the inhabitants of the intertropical regions, whose shadows at noon in one part of the year are cast to the north and in the other to the south, according as the sun is in the southern or northern signs.

Amphitheatre at Pompeii

Amphithe´atre, an ancient Roman building of an oval form without a roof, having a central area (the arena) encompassed with rows of seats, rising higher as they receded from the centre, on which people used to sit to view the combats of gladiators and of wild beasts, and other sports. The first amphitheatre at Rome was that constructed by C. Scribonius Curio, 59 B.C. The Colosseum at Rome is the largest of all the ancient amphitheatres, being capable of containing 100,000 persons, 87,000 of whom occupied numbered and reserved seats. That at Verona is one of the best examples remaining. Its dimensions are 502 feet by 401, and it is 98 feet high. The name means 'both-ways theatre', or 'theatre all round', the theatre forming only a semicircular building.

Amphitri´tē, in Greek mythology, daughter of Oceănus and Tethys, or of Nereus and Doris, and wife of Poseidon (or Neptune), represented as drawn in a chariot of shells by Tritons, with a trident in her hand. In the Homeric poems she is the personification of the Sea, and her marriage to Poseidon is alluded to in a number of scenes depicted on ancient monuments. Such are a bas-relief in the glyptothek at Munich and a mosaic in the museum at Naples.

Amphit´ryon, in Greek legend, King of Thebes, son of Alcæus, and husband of Alcmena. Plautus, and after him Molière, have made an amour of Jupiter with Alcmena the subject of amusing comedies.

Amphiu´ma, a genus of amphibians which frequent the lakes and stagnant waters of North America. The adults retain the clefts at which the gills of the tadpole projected.

Amphora
From a Roman specimen in the British Museum

Am´phŏra, a vessel used by the Greeks and Romans for holding liquids; commonly tall and narrow, with two handles and a pointed end which fitted into a stand or was stuck in the ground to enable it to stand upright; used also as a cinerary urn, and as a liquid measure—Greek = 9 gallons; Roman = 6 gallons.

Amplex´icaul, in botany, said of a leaf that embraces and nearly surrounds the stem.

Am´plitude, in astronomy, the distance of any celestial body (when referred by a secondary circle to the horizon) from the east or west points.

Ampthill, a market-town of England, Bedfordshire, about 7 miles south-west of Bedford. Pop. (1921), 2269.

Ampul´la, the Latin name for a vessel bellying out like a jug, which contained unguents for the bath; also a vessel