28 
TRANSACTIONS OF THE TEXAS ACADEMY OF SCIENCE. 
pier formula will result. Substitute the value of D from (9) in (11) and 
we get 
2 = Aa 2 X . 573r = .5014ra 2 
or nearly enough 
z = 0.5 rx* (12) 
a result identically the same as given by (7), thus showing that the cir- 
cular curve does not materially differ from the parabola previously as- 
sumed. 
