FLYING AND LEAPING. 43 



flying is, however, the ease with which the bird makes 

 the air a fulcrum, from which to leap, in that same 

 element, and that not only by repeated jerks or efforts, 

 which are characteristic of many of the smaller birds, 

 which thus leap from perch to perch, or from thicket 

 to thicket, but in the case of steady onward flight, in 

 which a few movements of the wings will sometimes 

 send the bird onward for many yards without any 

 other apparent movement ; and such appears to be 

 the impulse thus given, that the bird will sometimes 

 turn, and almost double back upon its former course, 

 by merely altering the inclination of the body and 

 wings, and without any new stroke or effort on the 

 part of these. The spring of the tiger, or the bound 

 of the antelope, though taken from the solid earth as 

 a fulcrum, and effected by what we consider as the 

 most powerful muscular action among the mammalia, 

 is a mere fraction in point of distance compared with 

 some of these gliding rushes of birds in the air ; and 

 it is worthy of remark, that birds'cannot take these 

 motions when they rise directly from the ground, or 

 from their perch, but must have a certain quantity of 

 fluttering, or hurried wing motion, to bring them up to 

 their power. 



We know that when any thing is projected for- 

 wards the resistance from which it is projected must 

 be equal to the projectile force ; for no mechanical 

 force can act in one particular direction only, unless 

 by means of resistance in the opposite direction. 

 Consequently, when a bird gives itself an impulse in 

 the air, in which mere gravitation to the earth can 

 bear no part, for that cannot bear a part, unless the 

 direction is downwards, its body must strike the air 

 backwards with a force equal to that which impels 

 it forwards ; and, if the body of the bird had not a 



