Page:Popular Science Monthly Volume 33.djvu/441

Rh and plants in detail, and as illustrating evolution, is in no sense a part of geography. Geography and history are related in their elementary stages, but diverge in their higher stages. The geographer must furnish to the historian the ideas and facts in science which he requires, and must go to the historian for the verification of the relations which he suggests. The body of laws governing those relations, which might in time be evolved, would render possible the writing of much "prehistoric" history. Mr. Green's "Making of England" is largely a deduction from geographical conditions of what must have been the course of history.

Water-Spouts in the Atlantic.—Many interesting reports in regard to water-spouts, sighted by masters of vessels during January and February of the Atlantic coast of the United States, have been received by the Hydrographic Office of the Navy Department. Water-spouts are a special class of whirlwinds, and their manner of formation is described as follows in a supplement to the "Pilot Chart of the North Atlantic Ocean" for March: "A layer of warm, moist air at the surface of the ocean happens to have above it a layer of cooler, drier air. This condition of things is one of unstable equilibrium, and sooner or later the warm, light air at the surface rises through the cooler and heavier air above. This process sometimes takes place gradually over large areas, but at other times it is more local, and there seems to be formed in the upper layer a break or opening through which the air of the lower layer begins to drain upward, as through a funnel. Under favorable conditions—that is, when the differences of temperature and moisture and the supply of warm, moist air at the surface are great—this action becomes very intense, and this intensity is still further increased by the fact that as the air rises its moisture is condensed, the latent heat thus liberated adding to the energy of the rising column of air. Now, as this surface air rushes in and escapes upward through the opening thus formed in the upper layer, it takes up a rotary or whirling motion, the velocity of which increases toward the center or axis of the funnel, and a suction or partial vacuum is created, as indicated by the low reading of the barometer at the center of a cyclone or whirlwind. When a whirlwind is thus formed over the ocean, water is often drawn up the center of the whirl some distance, owing to the suction created, and at the same time the moisture in the air is condensed as it rises, so that the name 'water-spout' is very applicable. Indeed, sometimes a spout will burst over a vessel and flood her decks with water, as a cloud-burst does a mountain-side. When a spout is forming, its upper portion is often visible first, seeming to grow downward from the clouds. By observing carefully with a telescope, however, it will be seen that the motion in the column itself is upward, although the moisture in the air which is rising is condensed lower and lower down, thus rendering the whirl visible lower down continually, and making it appear to be actually descending." That part of the North Atlantic from Cuba to the latitude of Philadelphia, and from the Atlantic coast of the United States to the Bermudas, is pre-eminently a region where water-spouts are liable to occur, owing largely to the warm, moist air lying upon the Gulf Stream, and the cool, dry air brought over it by the northwesterly winds from off the coast. Most of the water-spouts referred to were seen within this region. The Office wishes to receive many full and accurate reports of such marine phenomena, in order that knowledge of them may be increased. The most important observations regarding a water-spout are the temperature of the air and water, the reading of the barometer, direction and force of the wind, and the changes which take place in each while the spout lasts; also, the direction of rotation of the whirl, and an estimate of its size, character, and changes of form, with, if possible, photographs or sketches, however rough, of its appearance at the various stages of its formation and progress.

An Ancient Human Foot-print.—The discovery of human foot-prints in volcanic rocks near the shore of Lake Managua, Nicaragua, under circumstances which seemed to assign them a remote antiquity, has been announced for several years. Dr. D. G. Brinton has described, in a paper read before the American Philosophical Society, a specimen of these foot-prints, sent to him by Dr. Earl Flint, of Rivas, Nicaragua. The volcano of