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The winds appear to be caused by partial changes in the density of the atmosphere in a great measure arising from a diverse distribution of heat. When air is warmed it becomes less dense, or, in other words, it occupies a greater space. If an adjacent stratum of air be cooler, it will on coming in contact with the warmer air expand and pour into space occupied by the latter, thus forming a current. The greater the difference between the temperature of the one or other portion, the greater will be the force which the cold portion will rush into the space occupied by the warm portion, or, in other terms, the more violent will be the wind. In temperate climates the winds are variable; but in some parts of the world they blow with great regularity, and in others are subject to periodical changes.