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 in some degree the temperatures of the world, to carry off and distribute moisture where it is required, to sweep away noxious vapours, and generally to ventilate the Earth and gladden the heart of man.

The primary cause of all wind is the combined action of heat and cold. If the world were heated with perfect equality all round, there would be, as far at least as heat is concerned, a perfect and permanent stagnation of the atmosphere; and this would speedily result in the destruction of every living thing. But by the varied arid beautiful arrangements which the Almighty has made in nature he has secured a regular flow of atmospheric currents, which will continue unalterably to move as long as the present economy of things exists. The intense and constant action of the sun's rays in the torrid zone produces great heat, while the less powerful and frequently interrupted influence of his rays in the frigid zones induces extreme cold. Hence we have in one region heated air, in another cool air. Now, the effect of heat upon air is to expand it, make it light, and cause it to rise. The moment it does so, the cold air rushes in to supply its place; and this rushing in of the cold air is what we call wind.

It may surprise many people to be told that there are only two great and never-ceasing courses of the winds of this worldnamely, north and south. They flow perpetually from the equator to the poles, and from the poles to the equator. All the irregularities and interruptions that we observe are