The barometer only indicates real pressure when the atmosphere is in a state of perfect rest. It may then be represented a existing in vertical columns, but when it moves over a resisting surface its lower surface currents will be greatly retarded, while those aloft will move comparatively free and unimpeded. In this state it may be represented as moving in columns inclined in the direction towards which it moves. The atmosphere may thus be conceived as being divided into a number of spheroidal concentric layers, each of which is possessed of a different rate of speed, and moves more rapidly than the one beneath it: an increasing amount of friction will take place betwixt the layers as they approach the surface where its influence is greatest.