upon the Height of the Barometer. 



467 



ate heights of atmospheric columns being very materially 

 altered. 



The difference of temperature here supposed may be thought 

 too great, but the mean temperatures of the coldest month of 

 the year at Edinburgh and St. Petersburgh are given by 

 Humboldt at 38-3° and 8-6°, and yet there are only about 5° 

 of latitude between these cities. It is true that the two local- 

 ities are situated in different systems of climates, but the ro- 

 tation of the earth will cause the air of the West of Europe to 

 flow in the equatorial current towards the colder regions ot 

 Eastern Europe and Western Asia. 



Moreover, great falls of the barometer are always accom- 

 panied by an unseasonably high temperature. 



Storms in high latitudes are more frequent and violent in 

 winter than in summer, and as a necessary concomitant of this 

 fact, the oscillations of the barometer are greatest during the 

 former season. The difference in the force of the wind during 

 these seasons has been given numerically by A. FoUett Osier, 

 who laid before the last meeting of the British Association 

 for the Advancement of Science the results obtained by his 

 Anemometer during a space of three years. The strength of 

 the wind during the winter half of the year appears to be to 

 that in the summer half as 1000 to 530*. 



The cause of this difference is sufficiently obvious. 



The length of day increasing with the latitude during sum- 

 mer, and decreasing with it during winter, gives to high lati- 

 tudes a very great relative temperature in summer, and a pro- 

 portionately low one in winter. This is shown by the follow- 

 ing table given by Humboldt in his ' Essay on Isothermal 

 Lines;' it includes the longitudes between 1° west and 17° 

 east. The first column gives the mean temperature, the 

 second that of winter, the third the decrease of winter tempe- 

 rature in receding from the equator, and the fourth and fifth 

 the summer temperatures and decrease. 



The origin of atmospheric currents being the decrease of 

 temperature from lower to higher latitudes, their force will be 



• Report of British Association. Athenaeum, October 1840. 

 212 



