THE EUROPEAN STORM OF DECEMBER 21-28, 1836. n 



be found even warmer than the ordinary temperature of the earth's surface. But 

 generally, under a clear and tranquil sky, the reverse must be true. 



The atmosphere receives heat from the sun, and loses its heat by radiation. It 

 is estimated that in clear weather the atmosphere absorbs only about one-fourth of 

 the rays of the sun which traverse the atmosphere vertically. The remaining rays 

 are received upon the earth's surface, by which the earth is heated, and this" heat 

 is thence communicated to the air which rests upon the earth. Tlie heat which 

 the atmosphere receives is, therefore, chiefly applied to its lower stratum. This 

 heat is all lost by radiation ; for otherwise the mean temperature of the earth 

 would be continually increasing. The rate at which a hot body loses its heat by 

 radiation, is proportional to the difference between its own temperature and that 

 of the surrounding medium. Suppose, then, that a pound of air at tlie top and 

 bottom of the atmosphere contained the same amount of heat, the upper atmosphere 

 having on one side a void space whose temperature is many degrees below zero, 

 would lose its heat much more rapidly than the lower portion of the atmosphere. 

 The atmosphere, then, receives its heat chiefly at the bottom, and loses it most 

 rapidly at the top. The top must, therefore, ordinarily be the coldest, and such 

 would still be the case, thougli the atmosphere had throughout the same density. 

 In a clear and tranquil time, a pound of air at the earth's surface must, therefore, 

 contain more heat than a pound of air on the summit of a mountain ; and if air 

 from the summit of the mountain could be made suddenly to displace the air at the 

 level of the sea, it would feel colder than the latter. Such a condition of the atmo- 

 sphere is at best one of unstable equilibrium, and the lower strata tend continually 

 to rise and take the place of the upper. Such a motion is indicated nearly every 

 pleasant day, by the formation of cumulus clouds soon after the rising of the sun, 

 and their disappearance on the approach of evening. More violent and extensive 

 disturbances of this equilibrium take place in thunder-gusts and tornadoes, when 

 large masses of air from the earth's surface are pressed upwards with great violence, 

 and their place is occupied by air from the upper strata ; and the uniform effect of 

 such an interchange of air is a considerable reduction of temperature at the earth's 

 surface. After a few days' continuance of pleasant weather, the lower air again 

 becomes much warmer than the upper air, and another somerset takes place, accom- 

 panied by a like reduction of temperature. 



EUROPEAN STORM OF DECEMBER 21-28, 1836. 

 Observations of the Barometer. 



The following table presents a summary of the observations of the barometer at 

 each of the European stations from which reports have been received. Column 

 first shows the name of the station ; columns second and third their latitude and 

 longitude ; and column fourth the mean height of the barometer at each station. 

 The numbers in this column are in most cases derived from observations continued 

 through a series of several years, and represent the mean height of the barometer 



