INTRODUCTION. 



7 



the air with a speed little short of a cannon-ball, fills the 

 mind with wonder. Flight (if I may be allowed the expres- 

 sion) is a more unstable movement than that of walking 

 and swimming ; the instability increasing as the medium to 

 be traversed becomes less dense. It, however, does not 

 essentially differ from the other two, and I shall be able to 

 show in the following pages, that the materials and forces 

 employed in flight are literally the same as those employed 

 in walking and swimming. This is an encouraging circum- 

 stance as far as artificial flight is concerned, as the same ele- 

 ments and forces employed in constructing locomotives and 

 steamboats may, and probably will at no distant period, 

 be successfully employed in constructing flying machines. 

 Flight is a purely mechanical problem. It is warped in and 

 out with the other animal movements, and forms a link of a 

 great chain of motion which drags its weary length over the 

 land, through the water, and, notwithstanding its weight, 

 through the air. To understand flight, it is necessary to 

 understand walking and swimming, and it is with a view to 

 simplifying our conceptions of this most delightful form of 

 locomotion that the present work is mainly written. The 

 chapters on walking and swimming naturally lead up to those 

 on flying. 



In the animal kingdom the movements are adapted either 

 to the land, the water, or the air ; these constituting the three 

 great highways of nature. As a result, the instruments by 

 which locomotion is effected are specially modified. This is 

 necessary because of the different densities and the different 

 degrees of resistance furnished by the land, water, and air 

 respectively. On the land the extremities of animals en- 

 counter the maximum of resistance, and occasion the minimum 

 of displacement In the air, the pinions experience the mini- 

 mum of resistance, and effect the maxiinum of displacement; the 

 water being intermediate both as regards the degree of 

 resistance offered and the amount of displacement produced. 

 The speed of an animal is determined by its shape, mass, 

 power, and the density of the medium on or in which it 

 moves. It is more difficult to walk on sand or snow than on 

 a macadamized road. In like manner (unless the travailing 



