Proceedings of the American Philosophical Society. 35 



form and velocity of the atmospheric wave, the progress of vi'hich, over 

 the United States, he has represented upon a chart. 



2. A comparison of the observations of the thermometer and barome- 

 ter shows, that while the pressure was diminishing the temperature was 

 increasing, and vice versa. The very remarkable diminution of tempe- 

 rature of 48° Fah. in six hours and a half, occurred at one station in the 

 N. W. of the United States. The commencement of the diminution of 

 temperature is shown to coincide with the minimum of the barometer, 

 and hence is used when barometric observations were not made, to point 

 out the probable time of the occurrence of this minimum. The average 

 of the maxima of the thermometer at the eastern stations was about 3i° 

 Fah. greater than at the western, and the average of the minima 14° Fah. 

 greater. 



3. Rain or snow fell during the storm within the limits of about latitude 

 28° N. to latitude 48° N., and from longitude 52° to 96° W. The aver- 

 age amount at fifty nine stations, was seven eighths of an inch. The 

 author is led to remark upon the great discrepancies in the statements of 

 the fall of rain at places very near each other, and upon defects in the 

 registers in not stating the time of beginning and ending of the rain. 



4. The epoch of the minimum of pressure at the several places of ob- 

 servation was marked by a change of wind from a southern quarter, gen- 

 erally the southeast, to a northern quarter, almost uniformly the northwest. 

 This southern change of wind was every where one of the most promi- 

 nent features of the storm, the wind having been violent both before and 

 after the change ; but more violent from the northwesterly direction, ex- 

 cept perhaps at New York and in the northeastern states. 



The author sums up thus the characteristic of the storm. After a cold 

 and clear interval, with the barometer high, the wind commenced blow- 

 ing from a southerly quarter ; the barometer fell rapidly, the thermometer 

 rose, and rain fell in abundance. The wind subsequently veered sud- 

 denly to the northwest, and blew with great violence ; the rain was suc- 

 ceeded by hail or snow, which continued but for a short time. The 

 changes thus described occurred, not simultaneously, over the United 

 Stales, but progressively from west to east. 



The author next endeavors to determine the limits of the storm, using 

 for this purpose other meteorological registers in addition to those before 

 noticed, and of which he gives a particular account. From these, and 

 theoretical considerations, he places the Rocky Mountains as the western 

 limit, the parallel of 25 ' N. latitude as the southern limit, the middle of 

 the Adantic as the eastern limit,- and the northern as altogether conjectu- 

 ral, but probably as remote as the arctic circle, thus extending over 70° 

 of longitude and 40° of latitude. The question whether the remarkable 

 storm which occurred in Europe about the 25th of December, was a con- 

 tinuation of this storm, is examined, and the author concludes, from a 



