we may imagine our river straight, evenly broad and deep, with no marked channel, and without tributaries. The formation of a channel begins as soon as a bit of the earthy constituents contained in the water is deposited on the ground under it. This causes an unequal distribution of the weight of the water, and a stronger inclination toward one or the other edge. The deposit slowly grows, and a sand-bar is formed, which presses the current over toward one side and gives it an angular direction. This causes it to strike with more force against one of the shores, and to wash it, eat it away, or undermine it, equally whether it be of earth or stone. Should there be a tributary coming in from the opposite side of the sand-bar, that will occasion the formation of a second bar, and this will cause the current to make another turn and render its course serpentine. In this way a system of bars is formed, that are represented in the course of time by dry alluvial deposits, from which the river has been constantly pushed to one side. Many of the peculiarities of African and other rivers may be explained by reference to these principles. The great bends of the Congo and the Niger may be accounted for by supposing that the hills that run parallel to their courses were weathered most on the side most exposed to the sun so as to cause a constant growth of the bars on the north side and a gradual pushing of the stream toward the equator. In Hungary, the courses of the streams are modified by the operation of another force, that of the equinoctial winds called the koschava which blow in the spring and fall for days at a time from the southeast. The waves are driven by the wind, especially at the time of high water in the spring, with more force against the western bank, and make longitudinal excavations in it at the level of the water. After the retiring of the flood, the overhanging bank gives way and slides into the river, with a noise which is quite familiar to the people, and well understood by them. These excavations, extended and deepened by subsequent operations of the same kind, result in the formation of large bends; and the river has become very serpentine, with numerous narrow peninsulas jutting out at right angles to its current. Finally, the peninsulas are cut through and formed into islands, to become in time, as has been the case in some instances, by the operation of continued changes of the stream, a part of the other bank. Observations of this kind have been made in the Danube, and the phenomena accounted for by them are familiar on other rivers. Changes by another kind of process are caused by the fall equinoctial winds, which, instead of finding high water in their way, take up the dry sand and deposit it in drifts where they will exercise a modifying influence on the course of the river. The changes that have taken place in the Amou-Darya of Turkistan, under which its course has been diverted from the Caspian Sea to the Sea of Aral, are probably effects of an agency of this kind.
Russian Scientific Societies.—Science is promoted in Russia by several societies that are very active in their respective fields of investigations, and which have earned for their country a respectable place among the nations where knowledge is diligently and intelligently cultivated. The Kiev Society of Naturalists was formed in 1869, and is supported by a considerable membership. Its chief aim has been the exploration of the natural history of the neighboring provinces. Its published "Transactions" bear evidence of good work done in geology, zoölogy, botany, and kindred sciences. Since 1873 it has undertaken the yearly publication of a systematic catalogue of papers in mathematics, pure and applied, natural science, and medicine, printed in the numerous scientific publications of the empire. The East Siberian branch of the Russian Geographical Society, having already contributed largely to the purely geographical exploration of the unknown parts of Siberia and the adjacent countries, has now become engaged upon a more thorough scientific exploration of Siberia itself. Among its later publications is an excellent geological map of the coasts of Lake Baikal. The Siberian branch of the Geographical Society has within the last few years taken a lively interest in anthropology and archæology, and has been the means of making known many valuable discoveries in these branches. It has also paid much attention
