Aer is the first element in many compound words of Greek origin meaning air, the air, atmosphere; in this connection it is combined with motor, defined as a machine which transforms the energy of water, steam, or electricity into mechanical energy—in this instance, is meant the changing of the power of moving air or wind into mechanical energy.
Wind is air put in motion. There are two ways in which the motion of the air may arise. It may be considered as an absolute motion of the air, rarefied by heat and condensed by cold; or it may be only an apparent motion, caused by the superior velocity of the earth in its daily revolution.
When any portion of the atmosphere is heated it becomes rarefied, its specific gravity is diminished, and it consequently rises. The adjacent portions immediately rush into its place to restore the equilibrium. This motion produces a current which rushes into the rarefied spot from all directions. This is what we call wind.
Meteorology is the science which treats of the atmosphere and its phenomena, particularly of its variations of heat and cold, of its winds, etc.
This is the great division of science to which one has to turn when searching for the first principles relating to the operation of aermotor pumps. The vast volumes of air which flow “hither and yon” are controlled by physical laws which act as accurately and unceasingly as those which control and hold in check the seemingly solid substance of the earth itself.
Note.—The portions north of the rarefied spot produce a north wind, those to the south produce a south wind, while those to the east and west in like manner, form currents moving in opposite directions. At the rare spot, agitated as it is by winds from all directions, turbulent and boisterous weather, whirlwinds, hurricanes, rain, thunder and lightning, prevail. This kind of weather occurs most frequently in the torrid zone, where the heat is greatest. The air, being more rarefied there than in any other part of the globe, is lighter, and, consequently, ascends; that about the polar regions is continually flowing from the poles towards the equator, to restore the equilibrium; while the air rising from the equator flows in an upper current towards the poles, so that the polar regions may not be exhausted.
To sum up all observations, it can be said with truth that the sole force immediately concerned in causing the movements of the atmosphere, is gravitation.
So far as the prevailing winds are concerned it has been shown that where pressure is high, that is to say, where there is a surplus of air, out of such a region winds blow in all directions; and, on the other hand where pressure is low, or where there is a deficiency of air, towards such a region, winds blow from all directions in an in-moving special course.
This outflow of air currents from a region of air pressure upon a region of low pressure is reducible to a single principle, as already stated, viz., the principle of gravitation.