THE AMERICAN STORM OP DECEMBER 20, 1836. 7 



thermometer was above its mean height. For convenience we will call this area 

 the area of high thermometer. On the evening of December 19th this area of hi-h 

 thermometer extended from 800 to 1,100 miles in an east and west direction; but 

 at only three places did the thermometer rise as liigh as ten degrees above the 

 mean. December 20th the area of high thermometer near the parallel of 40° had 

 contracted to a breadth of 570 miles, and at several places the thermometer stood 

 more than fifteen degrees above the mean. On the morning of the 21st the ther- 

 mometer at several places stood more than twenty degrees above the mean. Thus 

 it appears that near the centre of the storm the heat had increased about fifteen 

 degrees in thirty-six hours, from the evening of the 19th to the morning of 

 the 2 1 St. 



The centre of this area of high thermometer did not coincide with the centre of 

 the area of low barometer, but was uniformly somewhat to the eastward of it. On 

 the morning of December 20th, near the parallel of 40°, the point of greatest heat 

 was considerably eastward of the centre of the area of rain and snow, and was 

 about 400 miles east of the point of least barometric pressure. On the evening of 

 December 20th, near the parallel of 44°, the point of greatest heat was about 350 

 miles east of the point of least pressure, and this last point coincided nearly witli 

 the centre of the area of rain and snow; while on the morning of December 21st, 

 near the parallel of 46°, the point of greatest heat was about 200 miles east of the 

 point of least pressure. On the eastern side of the storm, where the rain had not 

 yet commenced, the thermometer stood twenty degrees above its mean height; 

 while on the western margin of the storm the thermometer sunk below its mean 

 height before the rain and snow had ceased. On the evening of December 21st 

 the points of greatest heat and of least pressure probably differed but little in 

 position. 



Face of the Sky. 



On the five accompanying charts, the face of the sky has been represented by 

 colors in accoi'dance with the original observations, of which the most important 

 particulars are given in my article published in the Transactions of the American 

 Philosophical Society, vol. vii. pp. 133-137. From these charts it will be seen that 

 on the evening of December 19th rain or snow was falling throughout the entire 

 region west of the Mississippi, as far as the map extends, and the cloud covered 

 the entire United States, except those States bordering on the Atlantic Ocean. On 

 the morning of the 20th the rain and snow had extended eastward as far as Cin- 

 cinnati, and the cloud covered the entire United States, except New York and Xew 

 England. On the evening of the 20th the rain had extended eastward to "Wash- 

 ington, while only a small portion of New England was free from cloud. The 

 boundary of the rain and snow on the west now comes within the limits of the 

 chart, and an area of clear sky appears beyond Arkansas and Louisiana. On the 

 morning of the 21st the cloud has covered the whole of the eastern portion of the 

 chart, while the western portion is left unclouded as far as Cincinnati. The rain 

 now covers the whole of New England, except the State of ^Nfaine, while the western 

 boundarv of the rain and snow has reached the middle of T/ake Erie. On the 



