Winds transport particles of dust, and, with them, the minuter forms of vegetable and animal life, to vast distances. The phenomena known to sailors as _red fogs_ and _sea-dust_ are evidence of this. In the Mediterranean, and also in the neighborhood of the Cape Verde Islands, showers of dust, of brick-red or cinnamon color, are sometimes experienced in such quantity as to cover the sails and rigging hundreds of miles away from land. Among this sea-dust, examination with the microscope has detected infusoria and other organisms native to the tropical regions of South America. The prevailing currents of the atmosphere, or _winds_, constitute an important feature in the climate of any country, and it belongs to Physical Geography to explain the prevalent winds which distinguish great regions of the globe. Such explanation is more easily made in regard to the warmer latitudes of the earth, where alone the direction of the wind is constant, than might be at first supposed by those whose personal experience is limited to such countries as Britain, and other temperate lands, where the variable condition of the atmosphere is the well-known subject of common observation and remark. But within those parts of the globe which experience a vertical sun, and for a few degrees beyond the exact line which marks the limit of the sun’s vertical influence on either side of the equator, the conditions either of perennial calm, or of currents of air that constantly blow in one given direction, are the uniform characteristics of climate.