37 



barometric observations from 27 different stations within the United States 

 and the neighboring British possessions. I also obtained meteorological 

 journals, not containing barometric observations, from 28 military posts, 

 from 42 academies in the State of New York, and from five other stations; 

 making 102 in all, besides several stations beyond the probable limits of 

 the storm. 



In analyzing these materials, the barometric observations were all graphi. 

 caily represented by curves, showing the fall and rise of the barometer, 

 with the time of its minimum height. Then joining by a line all those 

 places where the minimum of the barometer occurred at tlie same instant, 

 we are furnished with the means of measuring the rate of progress of the 

 great atmospheric wave. On the southern border of the United States, this 

 velocity varied from 17 to 29 statute miles per hour; and on the northern 

 border from 17 to 37 miles. The leading characteristics of this storm were 

 as follows: After a clear and cold interval, with barometer high, the wind 

 commenced blowing from the south. The barometer fell rapidly; the 

 tliermometer rose; rain descended in abundance. The wind veered sud- 

 denly to northwest, and blew with great violence. The rain was succeeded 

 by hail or snow, which continues but a short time. The barometer rises 

 rapidly; the thermometer sinks as rapidly. These changes are experienced 

 progressively from west to east. 



This storm was not circular. The area of rain and snow was about 

 500 miles broad from east to west. Its length from north to south was 

 known to be 800 miles, and probably was not less than 1,500. For nearly 

 a day before the crisis, the wind blew from the southern quarter, and gen- 

 erally for several hours from the southeast. After the minimum of the 

 barometer, the wind blew with great violence from nearly the opposite point; 

 commonly the northwest. Here was clearly indicated a prevalent tendency 

 of the wind towards a central line: but, unfortunately, the observations em- 

 braced onlv one-half the area of the storm. The oscillation of the barom- 

 eter showed a steady increase from latitude 25° to Quebec. The centre 

 of the storm, therefore, could not have been south of Quebec, and north 

 of this place we could obtain no observations. 



I was now desirous of investigating a storm of marked characteristics 

 which could be entirelij surrounded, so that more of its features would 

 need to be supplied by conjecture. Two storms which occurred in Febru- 

 ary, 1842, appeared tolerably well suited to my purpose, and were selected 

 for a new investigation. Great pains were taken to collect materials from 

 every part of the United States. I succeeded in obtaining barometric ob- 

 servations from 64 different stations. I also procured registers, without 

 barometric observations, from 41 military posts, and 22 other stations, ma- 



