692 



WINDS OF THE GLOBE. 



S. W. Illinois . . 

 W. Kentucky . . 

 Middle Tennessee . 

 N. and Central Kentucky 

 N. W. Indiana . 

 S. E. Michigan . . 

 Toronto, Canada W. 

 N. E. Ohio . . . 

 W. New York . . 

 W. Pennsylvania . 

 Central New York . 

 N. W. Virginia 

 Central Virginia . 

 Middle N. Carolina 

 E. Tennessee . . 



14 27 



13 , 31 



6 40 



10 ! 31 



10 24 



9 26 



10 13 



8 31 



10 26 



23 25 



21 I 21 



11 i27 



8 '28 





^ 





03 



XD 



P= 



10 



17 



16 



15 



24 



10 



7 



27 



17 



11 



28 



19 



7 



28 



24 



6 :27 



5 ! 19 

 12 ,29 



10 127 



In the greatest part of this region S. W. and W. winds prevail winter and snm- 

 mer. Looking at the isobar-chart (Plate 14) we see that at all seasons the pressure 

 is higher in the region between the Gulf of Mexico and 35° N. L., and much lower 

 near the lakes ; hence there must be a south wind, which is converted into a S. W. by 

 the influence of the earth's rotation. In summer and autumn the pressure is gene- 

 rally higher in the south Atlantic States than in the same latitude further west, and 

 it would seem that S. E. and S. winds should be frequent from this cause. But the 

 Appalachians do not permit an exchange of air in the lower strata, and, as the 

 difference of pressure is but slight, S. E. winds Avill not often blow over the 

 mountain-chains. In the winter-months pressure is generally higher west of the 

 Alleghanies. Air is, so to say, heaped up by the prevailing S. W. winds. (See also 

 Maps, PI. 8, 11, and 14.) 



The daily weather-maps of the Signal Office show that the centres of storms 

 generally take a course nearly along the northern frontier of the United States, 

 especially in tlie region of the lakes. The monthly bulletins, in which the tracks of 

 the storm-centres are laid down, show this even more clearly. Besides this, very 

 low barometrical minima are comparatively seldom west of the Mississippi, and 

 the pressure generally diminishes in the centre of a storm the further it advances 

 towards the east. The storm-tracks then lie mostly to the north of the region 

 we are considering now. The winds during the passage of a storm must 

 then be S. W. and W. When the storm-track is more southerly, cold and dry 

 N. W. winds, in the rear of the storm, will be experienced. We see that in this 

 region the N. W. is frequently observed, especially in the winter. The storm-tracks 

 are, however, generally more southerly in winter than in summer. 



