If any doubt of the correspondence of the angles of mountains remains, I appeal to the sight of every man who makes the observation. Every traveller, with the smallest attention, will perceive that the opposite sides of a hill exactly correspond. Whenever the hills to the right of the valley form a projection, those opposite recede to the left. These hills have also nearly the same elevation, and it is very rare to see any great inequality of height in the two hills separated by a valley. I can assert, that the more I have looked on the circumference and heights of hills, the more I have been convinced of the correspondence of the angles, and of the resemblance they have with the beds and borders of rivers; and it is by reiterated observations on this surprising regularity and resemblance that my first ideas of this Theory of the Earth arose. Let us add to these observations that of the parallel and horizontal situation of the strata, that of the shells being dispersed throughout the earth, and incorporated in every matter; and it must be admitted, that on a subject like this we cannot have a greater degree of probability. ARTICLE XIV. OF REGULAR WINDS. Nothing can appear more irregular and variable than the force and direction of winds in our climates; but there are countries where this irregularity is not so great, and others where the winds constantly blow in one direction, and with almost the same degree of strength. Although the motion of the air depends on a great number of causes, there are nevertheless principal ones, of which it is difficult to estimate the effects, because of the modifications from secondary causes. The most powerful cause is the heat of the sun, which produces successively a considerable rarefaction in different parts of the atmosphere, and gives rise to an east wind that constantly blows between the tropics, where rarefaction is the greatest.