INSTRUCTIONS FOR MAKING PILOT BALLOON OBSERVATIONS 29 



In the meantime the recorder will enter the reading that he has made 

 in the proper colmnn on Form No. lUOA-Aer., and opposite the 

 corresponding minute. Suppose the azimuth angle for the first 

 minute, read by the recorder, is 203.4°; this he will record in the 

 column under "xizimuth angle" and opposite "1" in the minute 

 column. The observer then calls out the angle which he has read, 

 and the recorder enters this; e. g., "16.7°" in the column headed 

 "Elevation angle." 



85. During the time that is left between the readings, the recorder 

 will compute the values of the column headed "Distance from obser- 

 vation point" with the shde rule or look up the value in the horizontal- 

 distance tables. Explanation of the slide-rule process will be taken 

 up in following paragraphs. At the recurrence of the "warning" 

 signal all other duties will be suspended and the full attention of 

 both men given to the placing of the balloon on the cross hairs and 

 the accurate determination of angles. This same procedure obtains 

 so long as the observation is in progress. 



86. Use of telephones. — When the station is equipped with tele- 

 phones, the observer communicates the angles as read from the 

 theodolite to the computer at the plotting board. The computer 

 records the angles as received on Form No. lllOA-Aer., computes 

 the horizontal distance of the balloon for each minute by slide rule, or 

 looks up the value in the tables, plots these distances on the plotting 

 board, and obtains the wind directions and velocities therefrom while 

 the observation is in progress. The data necessary for telegraphic 

 or other purposes are, therefore, available immediately after the bal- 

 loon ceases to be observed. A computer with sufficient experience 

 may also accomplish the next step in the observation; that is, plot 

 the wind direction and velocity on Form No. 1115-Aer. 



87. In order to obtain maximum efficiency with telephones, the 

 following procedure should be followed: The computer first sets the 

 slide rule on the altitude to be read, then when the recorder reads the 

 elevation angle he immediately sets it on the slide rule while the 

 recorder is reading the azimuth angle. Next he records, on Form 

 No. lllOA-Aer., the elevation angle, azimuth angle, and the distance 

 which is already set on the rule. Note the elevation angle should 

 always be read first. The next step is to plot the distance on the 

 plotting board and to secure the direction and velocity for the preced- 

 ing minute. These data should be entered on Form No. lllOA-Aer. 

 and plotted on Form No. 1115-Aer. The altitude of the next minute 

 is now set on the slide rule and the procedure above described repeated 

 for each succeeding minute of the observation. 



88. One-man observations. — It is now the custom at most stations 

 for pilot-balloon observations to be made single-handed. In such 

 cases great care must be exercised to avoid losing the balloon while 

 the angles and horizontal distances are being recorded on Form No. 

 lllOA-Aer. The most efficient procedure to follow each minute, 

 especially when the balloon is moving rapidly across the field, is to 

 (1) read both angles, (2) move the balloon back near the portion of 

 the field /rom which it is moving, (3) record the angular readings on 

 Form No. lllOA-Aer., (4) again move the balloon back in the field, 

 (5) compute the horizontal distance by means of the slide rule or look 



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