BLAIR— AEROLOGY. 



193 



included. In addition to surface conditions it is well if a knowledge 

 of free air conditions to heights well above neighboring trees, build- 

 ings, hills or mountains can be known before deciding on the location 

 of a station. 



Fig. 5. Mean of Wind Observations in " Lows " at 526 Meters above Sea 



Level, 1907-1912. 



The course to be pursued by a pilot flying between two stations 

 should be governed by the structure of the atmosphere at the time 

 and places in question. A knowledge of the relations that have been 

 found to exist between surface and upper air conditions will be of 

 value to the pilot, but cannot in general take the place of direct ob- 

 servations. By means of the observations, results of which could 

 be available at the starting point of the course wnthin half an hour 

 after the observations were started, it would be decided whether 



