THE EUROPEAN STORM OF DECEMBER 21-28, 183G. 23 



Comparison of the Lines of Barometric and Thermometric Oscillation. 



It is very obvious from an inspection of the charts that the lines representing 

 the flvictuations of the barometer are very unlike those which represent the fluc- 

 tuations of the thermometer, and it is not easy to discover any connection between 

 them. In the United States, while the barometer falls during a storm of rain or 

 snow, it is common for the thermometer to rise, so that the area of low barometer 

 corresponds nearly to that of high thermometer, and the lines of equal barometric 

 disturbance bear a considerable resemblance to the lines of equal thermometric 

 disturbance. But in the storm of December 25th, throughout nearly all of Western 

 Europe, the thermometer was pretty uniformly depressed about ten degrees below 

 its mean height ; yet the barometer in Christiania stood four-fifths of an inch above 

 its mean height, while in North Italy it was about one inch helow its mean height. 

 Hence, we infer that change of temperature (as shown at the earth's surface) is not 

 one of the principal causes of the fluctuations of the barometer. While in North 

 Italy the barometer sunk an inch below the mean, the thermometer at the earth's 

 surface scarcely anywhere rose as much as five degrees above the mean. Yet heat 

 is always liberated when vapor is condensed, and we must hence infer that this 

 condensation took place at a considerable elevation above the earth's surface — at 

 an elevation greater than that of St. Bernard, which is more than 8,000 feet above 

 the sea ; for at St. Bernard there Avas a great fall of snow, but no rise of the ther- 

 mometer. 



It is also evident that the cause which produced the fall of the barometer in 

 Switzerland, operated at an elevation of more than 8,000 feet above the sea, for at 

 St. Bernard the oscillation of the barometer was as great as it was at the level of 

 the sea. 



On the 21st of December, in Russia, the area over which the thermometer was 

 ten degrees above the mean corresponded tolerably well witli tlie area of snow and 

 rain, but was a little displaced, overlapping on the southeast side, and falling short 

 on the northwest side. A similar remark is applicable to December 22d. 



On the 23d, throughout the whole of Europe, the area over which the thermo- 

 meter stood above its mean height exhibited nearly the same form as tlic area of 

 rain and snow, but was displaced towards the south, overlapping on the south side 

 and falling short on the north side. A similar remark is applicable to the 24th, at 

 least as far as respects the Russian part of the storm. 



The following is my explanation of these facts : In a great storm of rain and 

 snow, when vapor is condensed, heat is liberated, which raises the temperature of 

 the surrounding air above its mean height. This heated air is frequently wafted 

 off by an upper current, and the heat of the upper stratum is partially communi- 

 cated to the lower stratum, so that the area of high thermometer no longer corre- 

 sponds with the area of rain and snow. The displacement of the one surface, as 

 compared with the other, indicates the direction of this controlling upper current. 

 From the 21st to the 24th of December, 1836, this upper current in Europe appears 

 to have been from the northwest. 



