plate glass sides, and metal, slate or marble bottom and a metal frame. The botttom should be covered an inch deep or more with sand and pebbles scattered over it; and the tank filled with fresh river or spring water. The use of rock work adds greatly to the beauty. Among plants, water thyme, crowfoot, milfoil and starwort, are useful, because they produce a great deal of oxygen. Interesting animals for this purpose are the stickleback, goldfish, tench, gudgeon, perch, minnow and Prussian carp; while mussels and snails are good as purifiers. A saltwater aquarium needs more careful attention, but is built in much the same way. Another form, with three of the sides closed and with an inclined plane for a floor, to allow the more torpid animals easily to reach the surface, has been found very successful. Green dulse or seaweed is a good sea-plant to use, and of animals, shrimps, snails, barnacles, minnows and sticklebacks. Large aquariums have been built in many cities. One of the largest is the English one at Sydenham near London.
Aqueduct (ăk′wē-dŭkt), a channel for carrying water, or a structure on which water-pipes are laid. This method of carrying water has been in use from the earliest times. Persia, Judaea and many other eastern countries practiced it; while the Incas or rulers of Peru in the western world built aqueducts which have not been equaled in ancient or modern times. The Romans built these works all over their dominions. Rome was supplied by 24 aqueducts, some with several channels, one above another, extending many miles. They are built on a grade of regular descent, winding around the hills or piercing them by tunnels and supported across low levels by arches sometimes over a hundred feet high. Many cities are now supplied with water by this means. The Croton aqueduct, from the Croton river to New York city, is one of the greatest of modern aqueducts. Its construction cost $12,500,000, and five years were spent in building it. Its length is 4o½ miles, and there are 16 tunnels, cut mostly through the solid rock. An idea of the magnificence of this undertaking may be gained from the fact that the Harlem River is crossed by fifteen arches, seven of which are of 50 feet span, while eight are of 80 feet, the greatest height being 150 feet.
Other important aqueducts are those used for carrying canals across rivers and valleys. The chief examples in the United States are those on the Erie canal, 32 in number. At Pittsburg the Pennsylvania canal is carried across the Allegheny River upon a wire suspension aqueduct. Among the latest works of this kind is the new Croton aqueduct in New York, which cost over $20,000,000.
Aquinas (ȧ-kwī′nȧs), Thomas (c. 1225-1274), was the greatest of the Christian philosophers of the Middle Ages. He is known as "the angelical doctor" and "the universal doctor." Aquinas, so called because of his birthplace Aquino, in Italy, was a member of the order of Black Friars. His chief work is the Summa Theologiæ. His writings were regarded by his followers as almost sacred; and in 1323 he was canonised as Saint Thomas Aquinas. Although he knew little of history and nothing of Hebrew and Greek, the learning of Aquinas was as extensive as was possible previous to the Renaissance. In the 14th century scholars became divided into two great bodies, the Thomists or followers of Aquinas and the Scotists or the followers of the Franciscan writer, Duns Scotus. The doctrines of Aquinas somewhat resemble those of Aristotle, who was known in part to Aquinas in translation, and those of the Scotists are indebted to Plato. The great work of Aquinas was his attempt to bring together scientific learning and Christian doctrine into one complete system.
Ara′bia, an extensive quadrangular peninsula forming the extreme southwest part of Asia, much of the interior of which is an arid, sandy desert. It is situated between 12° 40' and 34° north latitude and between 32° 30' and 59° 40' east longitude.
Area. Its length, from north to south, is about 1,500 miles, and its breadth from east to west varies from 800 to 1,200 miles. It is bounded on the south by the Gulf of Aden, the Arabian Sea and Indian Ocean; on the east by the Gulf of Oman and the Persian Gulf, the Tigris River in the northeast separating it from Persia; while its northern boundary is Asiatic Turkey; and its western the Red Sea and Strait of Bab-el-Mandeb. The Sinaitic Peninsula and the Suez Canal on the extreme northwest separate Arabia from Egypt and the continent of Africa. In the southwest the island and fortified port of Aden and that of Perim both British possessions subject to the Bombay (East Indian) Government form excellent harbors and coaling stations. The other harbors (there are not many on the Arabian Coast) include Muscat on the Gulf of Oman, El Kuweit near the mouth of the Tigris, and Dafar (or Dhofar) near the British Kuria-Muria Islands in the Arabian Sea.
Government. The peninsula is politically a dependency of Turkey, and by that power its more settled region, on the Red Sea front, is created into two vilayets or provinces, named Hejas (area, 96,500 square miles, with a population of 300,000) and Yemen (area, 73,800 square miles, with a population estimated at 750,000). In the former (Hejas) the chief port is Jedda, the administrative seat and the
