156 NATURAL THEOLOG-Y. 



is in their imtrumenU of motion. These come before ua 

 under three divisions — ^feet, wings, and fins. I desire any 

 man to say which of the three is best fitted for its use ; or 

 whether the same consummate art be not conspicuous in 

 them all. The constitution of the elements in which the 

 motion is to be performed is very difi^erent. The anima! 

 action must necessarily follow that constitution. The Cre- 

 ator, therefore, if we might so speak, had to prepare for dif- 

 ferent situations, for different difficulties ; yet the pm-pose is 

 accomplished not less successfully in one case than in the 

 other ; and as between %oings and the corresponding limbs 

 of quadrupeds, it is accomplished without deserting the gen- 

 eral idea. The idea is modified, not deserted. Strip a wing 

 of its feathers, and it bears no obscure resemblance to the 

 fore-leg of a quadruped. The articulations at the shoulder 

 and the cubitus are much alike ; and, what is a closer cir- 

 cumstance, in both cases the upper part of the limb consists 

 of a single bone, the lower part of two. 



But, fitted up with its furniiure of feathers and quills, it 

 becomes a wonderful instrument, more artificial than its first 

 appearance indicates, though that be very striking : at least, 

 the use which the bird makes of its wings in flying is more 

 complicated and more curious than is generally known 

 One thing is certain, that if the flapping of the wings it 

 flight were no more than the reciprocal motion of the same 

 surface in opposite directions, either upwards and down 

 wards, or estimated in any oblique line, the bird would lose 

 as much by one motion as she gained by another. The sky- 

 lark could never ascend by such an action as this; for, 

 though the stroke upon the air by the underside of her wing 

 would carry her up, the stroke from the upper side, when 

 she raised her wing again, would bring her down. In order, 

 therefore, to account for the advantage which the bird de- 

 rives from her wing, it is necessary to suppose that the sur- 

 face of the wing, measured upon the same plane, is contract- 

 ed while the wing is drawn up, and let out to its ful) 



