362 ENVIRONMENTAL CONDITIONS. 



The average wind-velocities for the period of the average frostless 

 season, given in table 20, are presented in the form of a chart in plate 

 68. Perhaps the most striking features of this chart are the prevalence 

 of high average wind-velocities near the coasts and near the Great 

 Lakes and the apparently low average velocities encountered in the 

 mountain regions. In connection with the latter feature it is to be 

 noted that stations in mountainous regions are generally in valleys, 

 and are therefore protected from the general air-drift of the region. 

 This chart appears to be of Httle or no value in defining rational climatic 

 zanes; either the average wind-velocity per hour during the period of 

 the average frostless season is not a suitable feature by which to 

 measure climate as related to plants', or the data upon which our calcu- 

 lations have been based are too inadequate to bring out any relations 

 that may exist between this feature and plant distribution. We are 

 persuaded that both of these alternatives express the truth. The 

 average wind-velocity during the growing-season for plants is so little 

 different in different parts of the country, and the evaporating power 

 of the air is so greatly influenced by other conditions than wind, that 

 it seems hardly to be expected that average wind-velocity may prove 

 of great value in vegetational climatology. At the same time, if the 

 distribution of cUmatological stations and the methods of wind observa- 

 tion employed by the United States Weather Bureau should ever be 

 reorganized according to the needs of this sort of study, it is possible 

 that average wind-velocities might assume more importance than is 

 here apparent. A glance at the various heights of the anemometers 

 above the ground, as given in table 20, makes it clear that these instru- 

 ments have been placed rather for convenience than for the obtaining 

 of useful results, as far as chmatology is concerned. As Livingston 

 has remarked (1913), the population of the cities of the United States 

 may be estimated from decade to decade by the average height of the 

 Weather Bureau instruments above the ground; the instruments seem 

 to have risen higher in the air as the population has increased. This, of 

 course, is due to the pernicious habit of locating the recording-stations 

 generally in cities and towns instead of in the open country, where the 

 first principles of cUmatological study demand that such stations should 

 be placed. As towns have become cities and cities have enlarged, the 

 anemometers have been elevated from time to time, so that the back- 

 wardness of a town — as far as large buildings are concerned — may be 

 inferred from the low elevation of its Weather Bureau station. Table 

 20 shows that the anemometers are generally about 50 feet above the 

 ground in small towns. In New York City the anemometer is 314 

 feet above the ground, and for Pittsburgh (the highest elevation given 

 on our list) its height is 410 feet. 



When better wind data become available other hues of attack may 

 be begun, as, for instance, a study of the relation holding between 



