A Popular Treatise on the Winds (Electronic book text)

Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. Excerpt from book: Section 3CHAPTER III. THE GENERAL CIRCULATION OF THE ATMOSPHERE. INTRODUCTION. 61. THE motions of the atmosphere depend, either directly .or indirectly, upon differences of temperature. Without these the aqueous vapor would be uniformly distributed in all parts, there would be everywhere the same density, and a perfect calm in the atmosphere would exist over all parts of the globe. The great disturber of uniformity of temperature on the earth's surface is the unequal distribution of the sun's radiated heat. This gives rise not only to differences of temperature, but also to differences in the amount of aqueous vapor, in the air, from both of which causes the density of the atmosphere differs in different places, and thus atmospheric currents are produced. The forces, therefore, which overcome the inertia of the atmosphere when at rest and set it in motion, and which overcome the frictional and other resistances and maintain this motion t depend upon solar heat energy. Before entering upon the subject of the general circulation of the atmospherewhich, we have seen, is exceedingly elastic and, so far as we know, has no definite superior limit or surface it will be best to consider a few simpler cases of the motions of inelastic fluids. If any kind of liquid in a canal, or reservoir of any kind, or the ocean covering the greater part of the earth, had the same density in all parts and were at rest, the surface of the liquid in this case would be everywhere perpendicular to the direction of the force of gravity, and consequently coincide with, or be parallel to, the spheroidal surface of the earth, and the pressures in a horizontal direction on each side of any part of the fluid would be exactly equal, so that it would have no tendency to move in any direction. But if, from any cause, the fluid is...