ON THE 



AMERICAN STORM OF DECEMBER 20, 18.30, AND THE EUROPEAN 

 STORM OF DECEMBER 25, is;',(i. 



About twenty years ago, I undertook to investigate the phenomena of a violent 

 storm which swept over the United States about the 20th of December, 1836, and 

 the result of my investigations was published in the Transactions of the American 

 Philosophical Society, vol. vii. pp. 125-163. This storm extended from the Gulf 

 of Mexico to an unknown distance on the north. The fluctuation of the barometer 

 increased with the latitude, at least as far as Quebec, the most northern point 

 from which observations could be obtained. The area covered by the observations 

 included, therefore, only the southern half of the storm, and the phenomena of the 

 northern half could only be supplied by conjecture. I, therefore, regarded the 

 results of this investigation as unsatisflictory; but being unable to obtain observa- 

 tions from more northern stations, I published the information which I had obtained, 

 and sought for a more hopeful subject of investigation in the case of some storm 

 which was wholly embraced within the area of our observations. Such was the 

 storm of February 4, 1842, with regard to which I fortunately obtained abundant 

 materials for investigation. In conducting this investigation I adopted some 

 peculiar methods, which, so far as I have been informed, had never been practised 

 before. The phenomena of the storm, at intervals of twelve hours, were delineated 

 on a series of maps of the United States, in such a manner that every important 

 feature was made to appeal directly to the eye. 



Those portions of the map corresponding to places where the sky was unclouded 

 were colored blue ; those portions where the sky was overcast, but without nun or 

 snow, were colored brown ; those portions of the country where rain was falling 

 were colored yellow; and those portions where snow was falling were indicated by 

 a green color.' The direction of the wind was represented by arrows, and its force 

 indicated by their length. 



The observations of the barometer and thermometer were represeutcd in tlic 

 following manner: Having determined, as well as I was able, the mean lieiglit of 

 the barometer at each station, I compared each observation with the mean. I then 

 drew on the map a line connecting all those places where the barometer, at a given 

 hour, stood at its mean height. This line was called the line of mean pressure. I 

 then drew a line connecting all those places where tlie barometer, at the same hour, 

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