1403. It must be clear to the most common capacity, that as the rays of the sun descend perpendicularly on the surface of the earth under the torrid zone, that part of it must receive a greater proportion of heat than those parts where they fall obliquely; the heat thus acquired communicates to the air, which it rarefies, and causes to ascend, and the vacuum occasioned by this operation is immediately filled by the chill air from the north and south. The diurnal motion of the earth gradually lessens to the poles from the equator, at which point it moves at the rate of fifteen geographical miles in a minute, and this motion is communicated to the atmosphere in the same degree; but if part of the atmosphere were conveyed instantaneously to the equator from latitude 30ﾦ, it would not directly acquire the equatorial velocity; consequently, the ridges of the earth must meet it, and give it the appearance of an east wind. The effect is similar upon the cold air proceeding from the north and south, and the similarity must be admitted to extend to each place particularly heated by the beams of the sun. The moon, being a large body situated comparatively near the earth, is known to affect the atmosphere; and this, and the continual shifting of the point of the earth's surface over which the sun is vertical, to the west, are given as the causes of the tides and of the trade-winds. The moon's revolutions, by pressing the atmosphere upon the sea, cause the flux and reflux which we call tides; it cannot, therefore, be doubted, that some of the winds we experience are caused by the moon's motion.
