A PILOT BALLOON READY TO BE RELEASED 



Behind the observer is the specially constructed theodolite by which the track 

 of the balloon is observed and its direction and velocity measured at suitable 

 intervals. Valuable information is obtained by means of these balloons. It is 

 quite common for them to reach a height of four miles; sometimes they reach a 

 height of six miles before they are lost to sight. Larger registering balloons have 

 even reached fourteen miles. It was by means of these latter that it was dis- 

 covered that the air temperature does not go on decreasing after a certain height. 



