A. The sun heats the earth, and the earth heats the air resting upon it; as the warm air ascends, the void is filled up by a rush of cold air to the place, and this rush of air we call wind.
Q. Does the wind always blow?
A. Yes; there is always some motion in the air; but the violence of the motion is perpetually varying.
Q. Why is there always some motion in the air?
A. As the earth is always turning round, the vertical rays of the sun are always varying.
Q. What do you mean by “the vertical rays of the sun?”
A. The rays made at noon-day: when the sun is in a direct line above any place, his rays are said to be “vertical” to that place.
Q. How are the vertical rays of the sun always varying?
A. Suppose the brass meridian of a globe to represent the vertical rays of the sun; as you turn the globe round, different parts of it will pass under the brass rim, in constant succession.