perfected in higher animals. See Protozoa.
Amoor′ or Amur, a river of eastern Asia, 1,800 miles long. It forms a part of the boundary between Siberia and China, and flows into the Sea of Okhotsk. Length of river, including its chief tributary, the Argun, 2,800 miles, of which over 2,000 are navigable. In 1858, Russia had ceded to her the whole of the left bank of the Amur; since then, in taking possession of the Amur Valley, she has occupied much also of the right bank of the river. Amur is also a Russian province in Siberia, area 172,826 square miles; population, 119,909.
A′mos, one of the minor Hebrew prophets, lived about 800 B. C. He was a herdsman and a dresser of sycamore trees in the region of Tekoa, a fortified town south of Judah. He vigorously denounced the idolatry of the Jews, and prophesied the anger of God against idolatrous nations. His language is remarkable for its simplicity and clearness.
Ampère (än̄′ pâr′). The “practical unit” in which electric currents are measured. The numerical value of the ampere, as established by the International Electrical Congress, held at Chicago in 1893, is “the practical equivalent of the unvarying current which, when passed through a solution of silver nitrate in water, in accordance with standard specifications, deposits silver at the rate of 0.001118 grams per second.”
This definition, having been ratified by Congress, now defines the “legal ampere.”
The logical definition of the ampere, and the one which the legal unit approximates as nearly as possible, is “a current equal to one-tenth of the absolute unit of current.” See Electricity.
Ampère (än-pêr′), Andre-Marie (born 1775, died 1836). A distinguished French physicist and mathematician. Most of his working life was spent at the Ecole Polytechnique, the great military school of Paris.
Ampère’s most important contributions to knowledge are, perhaps, the three following:
First: His clear analysis and mathematical description of the work of Oersted. It was in the autumn of 1820 that Oersted discovered the effect of an electric current upon a magnetic needle. In less than one week after learning of this discovery, Ampère had extended the results by experiment and had reduced the description to a mathematical formula.
Second: The discovery that electric currents produce a magnetic effect upon each other: so that when the currents in two wires are flowing in parallel directions, they attract each other; but, when flowing in opposite directions, repel each other.
Third: Ampère introduced the very fruitful hypothesis that magnetic substances are made up of molecules in which electric currents circulate but meet no resistance. These currents are therefore permanent.
According to this view, a body is magnetized when its molecules are made to face more or less one way.
Amphibia (ăm-fĭb′ e-a), a natural class of vertebrate animals including frogs, toads, salamanders, newts, etc. The peculiarity about the amphibia is that they pass through a tadpole state. They are at first adapted to living in the water and breathe by gills and have no legs; but they gradually change; usually the gills disappear, and lungs and legs are developed. They are in a way intermediate between fishes and land animals. Sometimes the gills are retained throughout life, as in the mud-puppy (Necturus) and Mexican axolott. These forms have both lungs and gills. The salamanders are like lizards in form but are different in structure and development. Fossil amphibia are found imbedded in the rocks with a body as large as an ox. See Frog, Toad, Salamander, etc.
Amphithe′ater. See Colosseum.
Am′sterdam or Amsteldam, the capital and largest city of the Netherlands. The city is built on an arm of the Zuyder Zee, in the shape of a half-moon, and as the site is a marsh it is founded on piles driven deep into the mud. Dikes guard it against the tides, which rise higher than the city’s level. A system of canals with the river Amstel divides the city into about ninety islands, with nearly 290 bridges; hence the name of the city, Amsterdam, meaning “the dam or dike of the Amstel.” There are many fine public buildings, the finest being the palace, built in 1648. There are several public societies, such as the Society of Public Welfare, whose object is to promote education and the improvement of all classes, and which has branches in nearly every town and village of Holland. From a small fishing village in the 13th century, Amsterdam became, by the close of the 17th century, the first commercial city of Europe. After years of decline, it has again risen into commercial prominence. The Amsterdam canal, uniting the city (17 miles distant) with the North Sea, has recently been greatly enlarged and deepened, tidal locks being affixed at either end—the Zuyder Zee end and the North Sea entrance. Population 568,130.
Amsterdam, a city of Montgomery County, New York, 33 miles from Albany. It is an important manufacturing city, among its products being carpets, rugs, knit-goods, wagon-springs, paper, paper-boxes, silks and brooms. Besides, it has foundries and machine shops. Amsterdam is located on the Mohawk River and Erie Canal, and has the service of the West Shore and the New York Central railroad. The first settlement was made in 1778 and was known as Veedersberg until 1804. The present city was incorporated in 1885, and
