Page:The National geographic magazine, volume 1.djvu/68

 this chart shows very clearly the positions of warm and cold waves relative to such cyclonic systems: first there is this cool wave in rear of the eastern cyclonic system, then a warm wave in front of the system advancing from the coast, and finally a cold wave of marked intensity following in its train.

It was probably during the night of the 12th that the lowest barometric pressure and the steepest gradients occurred. Although several vessels report lower readings, yet a careful consideration of all the data at hand indicates that about the lowest reliable readings are those taken at 10 at Wood's Holl, Mass. (28.92), Nantucket (28.93), Providence, R. I. (28.98), and Block Island (29.00). The steepest barometic gradients, so far as indicated by data at hand, are also those that occurred at this time, and are as follows, taking Block Island as the initial point and distances in nautical miles: at New London, 26 miles, the barometer stood 29.11, giving a difference of pressure in 15 miles of .063 inch; New Haven, 62 miles, 29.36, .087; New York, 116 miles, 29.64, .083; Albany, 126 miles, 29.76, .090. At 7 the following day, very low readings are also reported: New Bedford, Mass., 28.91, Block Island, 28.92, and Wood's Holl, 28.96.

The chart for 7, March 13th, shows a marked decrease in the intensity of the storm, although the area over which stormy winds are blowing is still enormous, comprising, as it does, almost the entire region charted. From the Great Lakes and northern Vermont to the northern coast of Cuba the wind is blowing a gale from a direction almost invariably northwest, whilst westerly winds and low temperatures have spread over a wide tract of ocean south of the 40th parallel. North of this parallel, the prevailing winds are easterly, the isobars extending in a general easterly and westerly direction. At the storm center off Block Island the pressure is 28.90, but the gradients are not so steep as on the preceding chart, and the severity of the storm, both ashore and at sea, has begun to diminish. About this center, too, the isobars are noticeably circular in form, showing that, although it first formed as an elliptical area, it gradually assumed the character of a true revolving storm, remaining almost stationary between Block Island and Nantucket until it had actually "blown itself out," while the great storm of which it was a conspicuous but not essential part was continuing its eastward progress. The enormous influx of cold air brought down by the long continued northwesterly gale is graphically shown on this chart by the