18 



ANIMAL LOCOMOTION. 



uniformly accelerated, the space it passes through during any 

 time whatever is proportional to the square of the time. 



In the leaping, jumping, or springing of animals in any 

 direction (except the vertical), the paths they describe in 

 their transit from one point to another in the plane of motion 

 are parabolic curves. 



The legs move by the force of gravity as a pendulum. — The 

 Professor, Weber, have ascertained, that when the legs of 

 animals swing forward in progressive motion, they obey the 

 same laws as those which regulate the periodic oscillations of 

 the pendulum. 



Resistance of fluids. — Animals moving in air and water 

 experience in those media a sensible resistance, which is 

 greater or less in proportion to the density and tenacity of 

 the fluid, and the figure, superficies, and velocity of the animal. 



An inquiry into the amount and nature of the resistance 

 of air and water to the progression of animals will also furnish 

 the data for estimating the proportional values of those fluids 

 acting as fulcra to their locomotive organs, whether they be 

 fins, wings, or other forms of lever. 



The motions of air and water, and their directions, exer- 

 cise very important influences over velocity resulting from 

 muscular action. 



Mechanical effects of fluids on animals immersed in them. — 

 When a body is immersed in any fluid whatever, it will lose 

 as much of its weight relatively as is equal to the weight of 

 the fluid it displaces. In order to ascertain whether an 

 animal will sink or swim, or be sustained without the aid of 

 muscular force, or to estimate the amount of force required 

 that the animal may either sink or float in water, or fly in 

 the air, it will be necessary to have recourse to the specific 

 gravities both of the animal and of the fluid in which it is 

 placed. 



The specific gravities or comparative weights of diff*erent 

 substances are the respective weights of equal volumes of 

 those substances. 



Centre of grccvity.— The centre of gravity of any body is 

 a point about which, if acted upon only by the force of 

 gravity, it will balance itself in all positions ; or, it is a point 



