WILLSOX. — ALTITUDE OF AEROPL.YNE FLIGHTS. 



35 



probably less than 150 feet, corresponding to an uncertainty of about 

 24 feet in the deduced height and S" in the angular altitude at the 

 north station. 



In order that an intelligent judgment may be formed of the general 

 accuracy attained, of the nature and frequency of erroneous observa- 

 tions, which must always occur in such a series, of the possibility of 



200O 



1000 



Fir.ruK 3. S|)iral of Brookins, September 12, plotted from observutions of 

 Tublea 1 Mid 11. 



