468 Injluence of Atmospheric Curretits 07i the Barometer. 



ill proportion to the amount of the decrease, which we find 

 in winter to be to that in summer nearly in the ratio of two 

 to one, and accordingly the force of the wind varies nearly in 

 this ratio also ; whilst the proportionally increased difference 

 in the densities of atmospheric columns of different latitudes, 

 affords greater scope for elevations and depressions in their 

 relative heights, and consequently for variations in their press- 

 ure ; and thus increases the extent of the oscillations of the 

 barometer. 



The lines marking the oscillations of the barometer, coincide 

 in direction for great distances. For a confirmation of this 

 fact I must refer to those drawn or graduated lines inserted at 

 the end of Professor Daniell's ' Meteorological Essays,' which 

 are selected from the volumes of the Ephemerides of the 

 Meteorological Society of the Palatinate. 



It is clear that any elevation or depression of the atmo- 

 sphere must be communicated by the flowing of the upper 

 current to great distances, both in the direction of the meri- 

 dian by the proper course of this current, and laterally by the 

 rotation of the earth ; and from this it occasionally happens, 

 that fluctuations in the height of the barometer are caused by 

 circumstances occurring at a distance from the place of obser- 

 vation. Thus in December 182], the height of the baro- 

 meter at Tottenham, near London, was 27"83 inches on the 

 24-th ; and though windy weather prevailed at the time, yet no 

 storm of wind of any consequence succeeded this great de- 

 pression, but a like state of the barometer was extensively ob- 

 served at the same time on the Continent, and very tempest- 

 uous weather attended it far to the south of our island*. 



The deviations of these lines from the mean, decrease to- 

 wards the equator. 



The oscillations of the barometer in the more southern 

 latitudes, which are merely communicated from northern 

 parallels, will of course decrease in extent with their distance 

 from their origin ; and in those originating near the tropics, in 

 which latitudes the differences of temperature are so much 

 less, and so much less exposed to irregularities than in those 

 nearer the poles, that much less variation in the heights of at- 

 mospheric columns can take place in the former than in the 

 latter, the fluctuations of the mercury will be proportionally 

 slight. 



The extent of the oscillations of the barometer below the 

 mean height diminishes, and the extent of those above the 

 mean increases, from the temperate to the polar regions. The 



* Howard's Meteorological Journal. Annals of Philosophy, vol. xix, p. 159. 



