ICEBERG 109 ICELAND 30 atmospheres, the lowering of the tem- perature as it is released serves to freeze water even in summer. A still more simple and inexpensive process of pre- paring artificial ice is used in connection with the newly-perfected method of con- densing the atmosphere into a liquid. The rapid evaporation of liquid air ab- sorbs an immense amount of heat and everything brought into contact with it is frozen. ICEBERG, a mountainous mass of ice floating in the sea. Icebergs are pro- duced by the breaking off of great masses from glaciers which have de- scended into the sea. When numbers of icebergs freeze together, they form what are called "fields" or "packs," which are often of great extent, stretching across the ocean as far as the eye can reach, and often rising in perpendicular cliffs from 80 to 100 feet above the water. ICEBOAT, a triangular framework of wood, running by means of a sail — with broad end forward — on three skates or runners 3 feet long by 8 inches deep. There is but one large sail, usually tri- angular, fastened to a boom and yard, which may be over 30 feet in length. Such an iceboat may be steered by the rudder-skate in almost any direction not in the teeth of the wind, and may attain an average speed of 30 or 40 miles an hour, and sometimes as much as 65. The Hudson and the Shrewsbury rivers may be regarded as the Eastern head- quarters of this sport, and there are several iceboat clubs. ICE CRYSTALS, hexagonal figures with angles of 60°, which water always assumes when it passes from the liquid to the solid state. The crystals of ice can- not ordinarily be seen, because in freez- ing they are so crowded together; but in thawing, the heat rays act first on the outsides of the crystals, dissolving them to water. It was formerly supposed that ice was a brittle substance, and even as recently as 1850 the motion of glaciers was ex- plained by the fine splitting of the ice caused by the weight and pressure of the immense masses resting on the lower layers. The experiments made by Mc- Connell and Kidd in 1888 on the plastic- ity of ice seemed to establish the fact that single crystals were not plastic and that the plasticity of glacier ice as shown by Pfaff in 1875 was a mistake. The discovery made by Koch in 1885 that rods of ice laid on two sharp edges are loaded bent, but recovered their straight- ness when the weights were removed, seemed to be explained by the same prin- Vol. V- ciple. But further experiments made by McConnell and Miigge between 1890- 1895 showed that this elasticity is notice- able in some cases but not in all. This elasticity of the ice crystals is now re- garded as the true explanation of the movement of glaciers, even though it has not yet been proved that the yielding quality of the ice does not increase with the temperature. ICE CALORIMETER, a method of determining specific heats by means of ice. Black's calorimeter consists of a block of ice with a cavity in its center, with a cover of ice. The body, whose specific heat is to be determined, is raised to a certain temperature, and then put in the cavity. When the body falls to 32° F., the freezing point, it is wiped clean, as is the cavity itself, with a cloth previously weighed. The increase of weight in the cloth measures the ice con- verted into water, whence may be de- duced the specific heat of the body, the rule being that 79.25, or in round num- bers 80 thermal units, are needed to liquefy a pound of ice. ICELAND, an island belonging to Denmark; between the North Atlantic and the Arctic oceans, 250 miles from Greenland and about 600 miles W. of Norway; grreatest length, E. to W., 300 miles; central breadth, about 200 miles; area with adjacent isles, 39,756 square miles. Pop. (1919) 91,912. The coast line for a considerable extent on the S. E. is almost unbroken, but in all other directions presents a continued suc- cession of deep bays, affording a number of natural harbors. The interior is covered by lofty mountain masses of volcanic origin, many of them crowned with perpetual snow and ice, which, stretching down their sides into the in- tervening valleys, form immense glaciers. These icy mountains, which take the common name of Jokul, have their cul- minating point in Orafajokul, which has a height of 6,409 feet. Among the volcanoes the most celebrated is Mount Hecla, in the S., about 5,000 feet high. Numerous hot spi'ings or geysers are scattered throughout the island. There are numerous lakes and rivers. The most valuable mineral product is sulphur, of which the supply appears to be inex- haustible. The climate is mild for the latitude, but the summer is too cool and damp for agriculture. In the S. parts the longest day is 20 hours, and the shortest 4, but in tlie most N. extremity the sun at mid- summer continues above the horizon a whole week, and of course during a corre- sponding period in winter never rises. Cjc— H
