THE AMERICAN STORM OF DECEMBER 20, 1836. 



In accordance with the preceding numbers, the lines of equal barometric disturb- 

 ance have been drawn upon the five accompanying charts for Doc. 19th, 8 P. M. ; 

 Dec. 20th, 8 A.M. and 8 P. M.; and Dec. 21st, 8 A. M. and 8 P. M. On each 

 chart is drawn the line of mean pressure, as well as the line of two-tenths of an 

 inch helow the mean; two-tenths of an inch above the mean, etc. On each of these 

 maps there appears a large area over which the barometer was beloAV its mean 

 height. For convenience we will call this area the area of low barometer. On the 

 evening of December 20th this area of low barometer was 980 miles from west to 

 east; on the morning of December 21st it was 770 miles from west to east; and 

 on the evening of December 21st it was 650 miles from west to east. It is evident 

 that towards the north, the area of low barometer extended much beyond the limit 

 of the maps. The gi'eatest observed depression of the barometer (.72 inch) was at 

 Quebec, in latitude 46° 49' ; whence it is inferred that the area of low barometer 

 probably extended as far north as it did south of Quebec. On this supposition, 

 the area of low barometer December 21st extended about 3,000 miles from north 

 to sovith. This area constituted an oblong oval figure whose length was from two 

 to three times its breadth. This figure was not stationary, but travelled constantly 

 eastward. 



If the observations embraced the entire area of the storm, we could easily deter- 

 mine the approximate centre of the area of low barometer, and thus assign the 



