136 THE WORLD-ENERGY 



or force-center. So that no single body in all the uni- 

 verse is or can be free for a moment from the action of 

 an immeasurable complex of impressed forces. 



And this shows that the first law of motion is not 

 only negative, but that, taken literally, it presupposes the 

 case of a body not acted upon by external forces. That 

 is, taken literally, the first law of motion presupposes a 

 case that can never, by any possibility, be verified, or even 

 realized. " Every body continues in its state of rest, etc., 

 unless compelled by impressed forces to change that 

 state." But every body is perpetually subjected to the 

 action of impressed forces. Hence a state of " rest "is 

 wholly impossible for any body whatever. So, too, a 

 state of "uniform motion in a straight line" is equally 

 impossible for any body whatever, for the reason that 

 the impressed forces must have the effect to constantly 

 produce changes in the motion of the body. Thus, at 

 the surface of the earth, a falling body may seem to the 

 observer to move in a straight line. But the observer 

 has only to reflect that the earth itself is revolving on 

 its own axis, to be convinced that the real movement 

 of the falling body has the direction of a curve. And 

 when he reflects further that the earth is moving in 

 its orbit at the rate of nine miles or more each second, 

 he can but see that the curve described by a falling 

 body is a very complex one, the complexity becoming 

 incalculable when the movement of the solar system 

 through space is taken into the account. 



So, too, the velocity of the falling body, simply with 

 reference to the earth, is approximately calculable as a 

 rate at any given moment, the increment being virtu- 

 ally the same within narrow limits. Add to this the 



