1 



INTRODUCTION. 17 



no longer a matter of doubt. As the limits of the present 

 volume will not admit of my going into the several arrange- 

 ments by which locomotion is attained in the animal king- 

 dom as a whole, I will only describe those movements which 

 illustrate in a progressive manner the several kinds of pro- 

 gression on the land, and on and in the water and air. 



I propose first to analyse the natural movements of walk- 

 ing, swimming, and flying, after which I hope to be able to 

 show that certain of these movements may be reproduced 

 artificially. The locomotion of animals depends upon me- 

 chanical adaptations found in all animals which change local- 

 ity. These adaptations are very various, but under whatever 

 guise they appear they are substantially those to which we 

 resort when we wish to move bodies artificially. Thus in 

 animal mechanics we have to consider the various orders of 

 levers, the pulley, the centre of gravity, specific gravity, the 

 resistance of solids, semi-solids, fluids, etc. As the laws which 

 regulate the locomotion of animals are essentially those which 

 regulate the motion of bodies in general, it will be necessary 

 to consider briefly at this stage the properties of matter when 

 at rest and when moving. They are well stated by Mr. 

 Bishop in a series of propositions which I take the liberty of 

 transcribing : — 



" Fundamental Axioms, — First, every body continues in a 

 state of rest, or of uniform motion in a right line, until a 

 change is eff*ected by the agency of some mechanical force. 

 Secondly, any change eff'ected in the quiescence or motion of 

 a body is in the direction of the force impressed, and is pro- 

 portional to it in quantity. Thirdly, reaction is always equal 

 and contrary to action, or the mutual actions of two bodies 

 upon each other are always equal and in opposite directions. 



Of uniform motion. — If a body moves constantly in the 

 same manner, or if it passes over equal spaces in equal periods 

 of time, its motion is uniform. The velocity of a body moving 

 uniformly is measured by the space through which it passes 

 in a given time. 



The velocities generated or impressed on diff'erent masses 

 by the same force are reciprocally as the masses. 



Motion uniformly varied, — When the motion of a body is 



