52 National Geographic Magazime. 



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 p. m. 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, o-iving 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 a. m. 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 a. m., March 13th, shows a marked decrease in 

 the intensity of the storm, although the area over which stormy 

 winds ate 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 pre- 

 vailing 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 charac- 

 ter 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 enor- 

 mous influx of cold air brought down by the long continued 

 northwesterly gale is graphically shown on this chart by the 



