600 THE GLACIAL LAKE AGASSIZ. 



WINDS. 



The nearly level vast prairies are lully exposed to all currents of the 

 ail-, and during the most windy months, which are in the spring and autumn, 

 they seem very bleak to one who has previously lived only in districts 

 where the surface mostly receives a partial shelter from the force of winds 

 by the undulations of hills and vales and by the presence of forests and 

 trees cultivated for ornament and shade. The movements of the atmos- 

 phere on the prairie district of Lake Agassiz do not appear, however, to 

 exceed in their aggregate amount those on its wooded district, or on the 

 basins of the Laurentian lakes, or on the Atlantic seaboard. Exposed 

 places throughout these areas, as the tops of hills, are quite as severely 

 swept by gales as the prairies, where they are so much more observed 

 in the common experience of the people. One of the most desirable 

 improvements of the prairie homestead is the cultivation of rows of trees, 

 called wind-breaks, about the buildings. 



Winds, usually light, but on many days heav)^, are moving almost 

 continually over this area, with variations in their direction to every point 

 of the compass. From the hourly records of the velocity of the winds as 

 measured by self-registering anemometers during the seven years from 1883 

 to 1889, inclusive, their mean velocity for this whole period was 6.58 miles 

 per hour at St. Paul, 7.28 miles at Duluth, 8.81 miles at St. Vincent, and 

 8.39 miles at Bismarck. 



With these means it will be instructive to compare the records of 

 several stations in other parts of the country during the same time, which 

 show for Boston, Mass., a mean velocity of 11.18 miles per hour; New 

 York City, 9.30 miles; Washington, D. C, 5.39 miles; Savannah, 7.12 

 miles; Chicago, 9.01 miles; Cincinnati, 6.55 miles; St. Louis, 10.56 miles; 

 New Orleans, 7.26 miles; Omahn, 8.05 miles; Denver, 6.99 miles; Salt 

 Lake City, 5.18 miles; Portland, Oreg., 4.94 miles; San Francisco, 8.94 

 miles; and San Diego, Cal., 5.61 miles. Among sixty-six stations of the 

 United States Signal Service thus tabulated, tlie maximum mean velocity 

 of the wind is at Dodge City, Kans., 11.48 miles per hour, and the mini- 

 mum is at Lyuchbui'g, Va., 3.76 miles. The least windy station of the 



