308 



ANIMAL MECHANICS. 



where 



, Q' - 4P H 



(75) 



4P 2 " 



When a 9 is positive, equation (74) represents an hyperbola, 

 and the equilibrium of the muscle is stable ; and when x 1 is 

 negative, equation (74) represents an ellipse, and the equili- 

 brium of the muscle is unstable. 



If P, Q, R, be positive, it is evident from (75) that 

 m 2 and n 2 will have the same sign as 



and if this quantity become negative, the ellipse represented 

 by 



will be imaginary ; or, in other words, there will be no axis 

 of unstable equilibrium possible. 



(a.) Wing of the Albatross. —The following measurements, 

 taken from the wing of the Albatross, are made, as before, in 

 twenty-fourths of an inch : — 



Wing of Albatross. 



Angle. 



l-V 



I sin 9 



V sin 9 



o° 



3* 



+ 48 



+ 35 



5 



88 



+ 54 



+ 26 



10 



120 



+ 45 



+ 18 



l S 



136 



+ 3° 



+ 10 



20 



148 



+ 12 



+ 4 



25 



170 



- 6 



— 2 



30 



186 



- 28 



- 7 



35 



195 



- 5 2 



— 12 



40 



198 



- 74 



- i7 



45 



194 



- 103 



- 25 



