33 2 THE BOEDERLAND OF SCIENCE. 



is a point of extreme importance as respects the power 

 of flying. For though there are some birds which 

 seem to rise almost straight from the ground, yet 

 nearly all, and especially the larger and heavier birds, 

 have to acquire a considerable horizontal velocity 

 before they can take long flights. Even many of 

 those birds which seem, when taking flight, to trust 

 rather to the upward and downward motion of their 

 wings than to swift horizontal motion, will be found, 

 when carefully observed, to move their wings up and 

 down in such sort as to secure a rapid forward motion. 

 I have been much struck by the singularly rapid 

 forward motion which pigeons acquire by what ap- 

 pears like a simple beating of their wings. A pigeon 

 which is about to fly from level ground may be seen 

 to beat its wings quickly and with great power ; and 

 yet instead of rising with each downward stroke, the 

 bird is seen to move quite horizontally, as though 

 the wings acted like screw-propellers. I believe, in 

 fact, that the wings during this action do really act, 

 both in the upward and downward motion, in a manner 

 resembling either screw-propulsion or the action by 

 which seamen urge a boat forward by means of a single 

 oar over the stern.* The action of a fish's tail is not 

 dissimilar; and as the fish, by what seems like a simple 

 beating of its tail from side to side, is able to dart 

 swiftly forwards, so the bird, by what seems like a 

 beating of its wings up and down, is able when occa- 



* Sailors call this sculling, a term more commonly applied to the 

 propulsion of a boat by a single oarsman using a pair of oars, or sculls. 



