172 COVERING OF ANIMALS. 



A. On account of its peculiar lightness, smooth- 

 ness, and warmth, it is singularly adapted to the uses 

 of the animal. A. bird's wing is a mechanical won- 

 der. It may be doubted whether the most ingenious 

 artist would have hit upon the construction, till he 

 had seen it exemplified. He would have known there 

 should be something to spread out, and be capable of 

 folding up, and that it should be very light, and suffi- 

 ciently strong, at the same time, to make a stroke 

 upon the air. The probability is, he would have 

 thought of a thin membrane like a piece of cloth, 

 so contrived as to open and shut like a fan, which is 

 actually the plan which has been adopted in artificial 

 wings. But there must be one unavoidable imperfec- 

 tion in such a wing. If accidentally torn, it would 

 be ruined for the bird's use. This difficulty is avoided 

 in the bird's wing by the only imaginable contrivance 

 which could have answered the purpose ; and that 

 is, having the wing composed of distinct feathers, suffi- 

 ciently close, when united, to give the necessary stroke, 

 but separating in case of any uunsual violence that would 

 endanger a membrane, and then recovering their places 

 by their own elasticity or springiness. Such is the struc- 

 ture of a bird's wing. Its ingenuity will still further 

 appear, when we examine a single feather. If the 

 beard or vane of a feather, that part we usually strip 

 off when we make a pen, be stroked down toward the 

 hollow or quill part, we find the little filaments or 

 threads will stand out from the stem, and remain sep- 

 a rate ; but if they are smoothed back in their places 

 l hey will reunite and become fastened together with 



