OF THE UNITED STATES ARMY. 



137 



leak and failed to ascend further. Graph No. 8 shows the fluctua- 

 tions which are often found at low altitudes, these fluctuations being 

 undoubtedly due to ascending and descending currents. 



Uniform rate of ascent of pilot balloon up to ii,ooo meters. 



The extreme constancy in the rate of ascent, shown in a great 

 majority of flights, although surprising enough, is not as inexplicable 

 as it at first appears, for since the pressure within the balloon due 

 to the tension of the rubber itself is only from five to eight centi- 

 meters of water, and since this pressure is at sea level less than i 

 per cent, of the pressure of the atmosphere, it will be seen that the 

 balloon will expand practically freely, that is, as though the walls 

 did not constrain it at all, up to heights of say 10,000 meters where 



