LIQUID 493 LISSA varied with the temperature, liquefaction began. At a temperature above 30 9°C, however, he found that it was impossible to liquefy carbon dioxide, no matter what pressure was employed. He ob- served similar phenomena in the case of nitrous oxide, and concluded that for every gas there is a definite temperature above which it cannot be liquefied. This temperature he called its critical tem- perature. It was now clear that the failure of Natterer, and others, to liquefy certain gases was due to the fact that the temperatures used by them were above the critical temperatures and the attention of workers on the subject was turned to the production of extreme cold. In 1877 Louis Cailletet succeeded in liquefying both oxygen and carbon monoxide. He found that by compress- ing a gas at a low temperature and then suddenly releasing the pressure, a marked drop in temperature occurred, and it was by utilization of this fact that he and later workers succeeded in lique- fying in turn all the "permanent gases." Liquid air and oxygen were produced in large quantities as a result of Dewar's experiments, and Hampson and Linde, in 1895, introduced the method of self- inteiisive refrigeration, in which the gas to be liquefied is continuously supplied through an apparatus in which it is cooled by expansion, and each portion of gas, after such cooling, is utilized in cooling the succeeding portion, until the cumulative effect produces liquefaction. LIQtjrp, a fluid; a material substance the particles of which have a perfect freedom of motion, without any sensible tendency to approach to or recede from one another, except by the action of some external power. Liquidity, as a condition of matter, is therefore compre- hended in the condition of fluidity. The particles of a liquid are held together with considerable force, notwithstanding their freedom of motion, since a small quantity of a liquid has a tendency to take a spherical form when at a distance from any substance for which its par- ticles have greater affinity than for one another. This is particularly apparent in mercury, oil and water. The form of the dewdrop is also another familiar in- stance. liquid air. see liquefaction of Gases. LIQUOR TRAFFIC. See Prohibi- tion. LISBON (Portuguese, Lisboa; an- cient Olisipo), the capital of Portugal, province of Estremadura, on the Tagus, near its mouth. The city is partly built Vol. V— on the shores of the Tagus, and on sev- eral small hills, and presents a magnifi- cently picturesque appearance from the river. The most beautiful part is called the New Town, stretching along the Tagus, and is crowded with palaces. The principal public squares are, the PraQa do Commercio, 565 feet long; and the Pragado Rocio, 1,800 feet long. The churches are profusely decorated, and some of thorn are built of marble. Among other architectural curiosities the most important is the Alcantara aqueduct, which supplies all the public fountains and wells of the city. Its course is partly underground, but as it crosses the deep valley of the Alcantara near Lisbon, it is carried over 35 marble arches for a length of 2,400 feet. Lis- bon contains a large number of educa- tional and scientific institutions, among which are the Royal Academy of Sci- ences, founded in 1778, a naval academy, and an academy of engineering. The harbor, or road, of Lisbon, is one of the finest in the v/orld; and the quays, which extend nearly 21/2 miles along the banks, are at once convenient and beautiful. The exports comprise vdne, oil, fruit, and salt; among the imports are woolens, cottons, silks, metals, colonial |)roduce, and furs. The manufactures of Lisbon are inconsiderable, consisting chiefly of silk fabrics, jewelry, paper, and soap; there are also sugar refineries, tanneries, and potteries; and its jewelers and gold- smiths are among the most expert in Europe; but its backwardness is owing principally to a want of energy and in- dustry. The climate of Lisbon is vari- able, but, on the whole, healthful and genial. Pop. about 436,000. LISSA (Polish, Leazno), a town of Prussia, 40 miles S. by W. of Posen; was during the 16th and 17th centuries the headquarters of the Bohemian Brethren in Poland; here were their most celebrated school, a seminary, a printing office, and their archives. The town grew up round a colony of that sect, to whom the Leszczynski family afforded an asylum early in the 16th century. It was burned by the Poles in 1656, and again by the Russians in 1707. Pop. about 17,000. LISSA, an island of Dalmatia, in the Adriatic Sea, 32 miles S. W. of Spalato; area, 40 square miles; is mountainous, grows good wine and olive oil ; pop. about 9,000. Fishing is the chief occupation. The island was held by Great Britain from 1810 to 1815. Off it the Italian fleet was defeated by the Austrians un- der Tegethoff on July 20, 1866. The Italian admiral, Persano, was next year Cyo — FE
