Page:Physical Geography of the Sea and its Meteorology.djvu/445

Rh to the north of her, as at C, where the air ascends as fast as it comes pouring in from all sides. The ship, let it be supposed, is just on the verge of, but exterior to the vortex, or that place where the wind commences to revolve. The first rush of the air at a will be directly for the centre C; consequently, a ship so placed would report the storm as commencing with the wind at south. For the sake of illustration, we will suppose this place of low barometer to be stationary, and the air, as it rushes in, to ascend at the disc C. Thus the area of inrushing; air will gradually enlarge itself by broad spreading, like a circle on the water, until it be compassed by a circle with a radius C S, of indefinite length. The air then, on the meridian S C N, but to the south of a, will not blow along this meridian and pass over the ship; in consequence of the diurnal rotation of the earth, it will take a direction, S a', to the westward; and the arrow d a, representing a S.S.E. wind, will now show the direction of the wind at a. Thus the ship will report that the wind commenced at south, and gradually hauled to S.S.E., i.e. against the hands of a watch; and so the arrows b a will represent the direction of the wind at each station, a a a when the storm commenced, and the arrows d a' the directions afterwards, thus showing it to have veered against the hands of a watch. And this is the direction in which the forces of diurnal rotation, when not