86 Our Climatic Vicissitudes. [February, 



example: at Farmer's College, on the 20tli of January, 1854, the ther- 

 mometer, at 2 P. M., stood at 54° ; at 7, next morning, it stood at 10°, 

 a fall of forty-four degress in seventeen hours. This suddtn fall was 

 occasioned by a change of wind, from the south around to the north-west. 

 Again : February 2d, same jear, the thermometer, at 7 A. M., was at 

 61°; next morning at the same hour, it stood at 14°. Once more: 

 March 17th, of the same year, the thermometer, at 2 P. M., stood at 

 71°, and the wind south-west. At 7, next morning, the thermometer 

 stood at 27°, with the wind north-west. Another change of forty-four 

 degrees in seventeen hours. 



Such changes are common in this region, and are still more sudden 

 and violent in the open prairie lands, where the wind, unimpeded by 

 bill or forest, whips about from one point of the compass to another, with 

 amazing rapidity. An old resident of Illinois says, that one winter day, 

 at 9 o'clock, A. M., the mud in front of his school-house, where he was 

 teaching, was so soft and deep that a horse could scarcely get through it. 

 At 4 o'clock in the afternoon of the same day it was frozen so hard that 

 a heavy wagon passed over it, without breaking through. 



Changes like these are wholly unknown in England. There, the 

 thermometer has a limited range, rarely rising above 70° in summer, or 

 desoenJing below 20° in winter ; while here, the mercury dances up 

 and down the tube, through an extreme range of one hundred and 

 twenty-five degrees ! 



What can be the cause of our unsettled weather — of these great and 

 sudden changes? 



Mr. Russell, a scientific Scotchman, who traveled extensively in this 

 country, says that it is owing, chiefly, to the modifying influence exercised 

 by the Eocky Mountains upon the great aerial currents of the globe. 

 Every school-lioy is aware that the ascent of the heated air at the equa- 

 tor causes the flow of an under-current from the north-east toward the 

 tropics, while an upper-current, in the opposite direction, restores the 

 equilibrium. As the north-east trade- wind approaches the equator, it 

 gradually turns more directly west, and if we follow it across the Atlan- 

 tic, we shall see that when it strikes against the towering Cordilleras of 

 Mexico, it will be gradually deflected northward, along their eastern 

 slope, and finally overflow the whole Mississippi valley, producing in 

 ■ summer those extreme heats, for which this region is remarkable, when 

 the thermometer, even as far north as Chicago, rises nearly to 100° 

 in the shade. Even in the winter it frequently brings the thermome^ 

 ter above 60°, generally making that lovely weather, occasionally known 

 to our winters, when a warm, golden mist fills the whole air. 



