INSTRUCTIONS FOR MAKING PILOT BALLOON OBSERVATIONS 39 



In general it may be stated, to find the wind direction for any one 

 minute rotate the protractor until the adjacent points of horizontal 

 projection on either side, with the latest numbered point of the 

 group toward the operator, are directly over the scale base or a line 

 parallel to the scale base, and read the direction in degrees on the 

 edge of the protractor coincident with the index line of the scale base. 

 120. A north wind will be designated as 360°, east as 90°, south as 

 180°, and west as 270°, etc. Since the balloon travels with the wind. 



Arlington, Vs. 



; ., "J p . 



Jan. 2B, 1936, 

 , ., W.333 



Willis A. Wood 



FiGURK 12. — Graphing board for construction of wind direction and velocity graphs oh Form No. 1115-Aer. 



it usually moves away from the observer and, owing to the fact that 

 angles of azimuth are read on the opposite side of the instrument from 

 the balloon, it has been found best to set the zero of the base plate on 

 south when orienting the theodolite for an observation. This is well 

 borne out when determining the direction of the wind movement 

 from the plotting board, as described above. When the theodolite 

 has been oriented with zero on south, the resulting direction of points 

 can be read from the index of the scale base on the near edge of the 

 board. 



121. Some operators may prefer to apply the wind scale to the 

 points for velocity and then, using the scale as a straight-edge to aid 



