ABSTRACT
The winds that transport heat and moisture, and that drive the ocean currents, are at once the operating mechanism and the working substance of climate. Whenever the moving air is deflected upwards, or rises in a convection current, it undergoes ‘expansion cooling’ — i.e. its temperature falls ‘adiabatically’ as described in a later paragraph — so that clouds and mist are commonly formed from the moisture in it: and processes going on in the clouds are liable to produce drizzle, rain, snow, etc., and, when the vertical motions are violent enough, thunder and hail. To understand how the wind circulation is related to the initial heat supply from the sun, and to the pattern of derived heat sources on the Earth and within the atmosphere, is the foundation of all that follows — of the whole science of weather forecasting, of our interpretation of past climates and present climatic development, and of any prospect of rational prediction of future climates.
