If experience is any guide, we learn that the motion of the revolving body is either partially or entirely transmitted to the liquid or gaseous medium surrounding such a body. So far as our experience teaches us anything, it teaches us that to that rule there is no exception, and no experiment can be devised of any body revolving in water or a gaseous medium as air, without that body imparting its rotation to the water or the air. The atmosphere in relation to the earth is no exception to this rule. We know that the earth has an equatorial circumference of about 24,000 miles, and that it revolves on its axis once every day, so that at the equator the surface of the earth is whirling round in space at the rate of 1000 miles per hour. Try to conceive what the result would be if the atmosphere were stationary at the earth's surface in the equatorial regions. It would mean that any body on its surface would be whirled round at that rate, while the atmosphere, being stationary, would exert a power equal to a wind travelling at the rate of 1000 miles per hour. Under the influence of such a hurricane, nothing could exist on the surface of the earth at the equator, if the earth revolved on its axis and the atmosphere did not participate in that motion. But the atmosphere is gravitative, and being gravitative, it is not only held bound to the earth as it revolves on its axis in its onward rush through space, but accepts the revolving motion of the earth, with the result that as the earth revolves on its axis, the atmosphere revolves also. Thus a balloon at the equator if allowed to rise several hundred feet above the surface could remain comparatively stationary if held by a rope to overcome its tendency to rise, whereas such an event would be impossible if the atmosphere failed to receive only half of the motion of the earth's surface, as it would still have a power equal to that of a wind blowing at the rate of 500 miles an hour. If, however, we come further north, or go further south, then we find that the surface of the earth does not have the same velocity as at the equator, with the result that the atmosphere has not the same velocity either; consequently it would travel slower in the temperate regions than in the equatorial regions, and slower still at the poles than in the temperate regions. We know by experiment what the effect of increased velocity has upon any whirling body; it tends to enlarge the body at those parts where the velocity is the greatest, the consequence being that the bulging out of the atmosphere would be greatest at the equator. We find a similar result in the shape of the earth, where the equatorial diameter is greater than the polar diameter, because of the centrifugal force being greatest in the equatorial regions.