296 ANIMAL MECHANICS. 



of 5 0 each, gives the following measurements in thirty-seconds 

 of an inch : — 



Wing of Heron. 



Angle. 



I -I'. 



I cos 9. 



v cos e. 



o° 



28 



47 



22 



5 



38 



55 



'9 



IO 



48 



65 



18 



!5 



65 



81 



17 



20 



83 



99 



16 



25 



100 



1 ' 3 



14 



30 



in 



124 



13 



35 



121 



130 



1 2 



40 



126 



132 



1 1 



45 



122 



123 



10 



From these measurements, I obtained the following results, 

 by calculation : — 



Wing of Heron. 



Angle. 



1 



(i + v ) cos e 



IV eos ? 0 





l- V 



I- I' 



o° 



0.03571 



2.4649 



3 6 -93 



5 



0.02632 



1.9474 



27.50 



10 



0. 02083 



1.7292 



2 4.37 



15 



0.01539 



1.5077 



21. 18 



20 



0.01 205 



1.3855 



19. 08 



25 



0. 0 1 000 



1 . 2700 



15.82 



30 



0. 00901 



I. 2342 



14.52 



35 



0. 00826 



I. 1736 



I2.00 



40 



0. 00794 



I. 1349 



II.52 



45 



0. 008 19 



I . 0901 



IO.08 



Sum, 



0.15370 



14.9375 



193.90 



Hence we find, for the centre of the conic (66), 



