The Laws of Motion. 227 



This is not the fact ; for the ball falls down by 

 the side of the mast, as if the ship were at anchor. 

 Why? Because the ball is under the influence 

 of two forces ; one horizontal, by the motion of 

 the ship, which is the same as if you had sent it 

 forwards from your hand with the same degree 

 of velocity as the ship moves at ; the other force 

 is perpendicular, by the power of gravity : so 

 that though it appears to fall perpendicularly, 

 it does not, but describes, in space, the same 

 kind of semi-parabola as a ball shot from a gun. 



If I throw a log of wood into the Thames, 

 when the wind is across the river, the log will 

 not obey the current, by going down the river, 

 nor the wind, by going across the river, but will 

 go in an oblique direction made up of the two. 



The third law is, that " re-action is always 

 equal to action." Thus, in consequence of this 

 principle, the resistance of a body at rest, which 

 is acted or pressed upon, acts against a moving 

 body with a certain degree of power, and produces 

 the same effects as an active force would have 

 done in the same direction. Thus, if I strike 

 an anvil with a hammer, the anvil exerts against 

 the hammer the same force with which it is struck 

 itself. Hence a common trick in the country, 

 of a man lying on die ground with a large anvil 

 on his breast, and suffering a strong man to 

 strike it with a sledge hammer with all his 

 might. If the anvil be very large, its vis inertke 

 resists the force of the blow, and the man is 



