WIND 



75 



itats, but the chance of error is great, except when the breeze is steady. 

 Anemographs alone give real satisfaction. Accurate results, however, are not 

 obtainable without a series of two or more in different habitats, and it is 

 still an open question whether the results obtained justify the expense. For 

 a completely equipped base station, anemometer, anemograph, and wind 

 vane are desirable instruments, but the study of the habitat has by no 

 means reached the stage of precision in which their general use is 

 necessary. 



109. The anemometer in its simplest form is adapted only to readings 

 made under direct observation, as a sudden change in the direction of the 

 wind reverses the move- 

 ment of the indicator 

 needle. This simple wind 

 gauge, shown in figure 

 23, has been used for in- 

 structional purposes, and 

 to a slight extent, also, in 

 ascertaining the effect of 

 cover. In constant winds, 

 successive single readings 

 are found to have value, 

 but, ordinarily, the obser- 

 vations must be simultane- 

 ous. Careful tests of this 

 simple instrument show that 

 it is essentially accurate. 

 It may be obtained from 

 the C. H. Stoelting Com- 

 pany, 31 W. Randolph St., 

 Chicago, for $25. The 

 standard anemometer 

 (Fig. 24) is practically a 

 recording instrument up to 1,000 miles, but as the dials run on without 

 any indication of the total number of revolutions, it must be visited and 

 read each day. This renders its use difficult for habitats which are some 

 distance apart. When exact determinations of wind values become neces- 

 sary, the most successful method is to establish a series of three standard 

 anemometers. One of these should be placed upon the most exposed part 

 of a typically open habitat, the second in the most protected part of the 

 same habitat, while the third is located in the midst of a representative 

 forest formation. If the two habitats are close together, the daily visits 



Fig. 24. Standard anemometer. 



