IN THE ANIMAL ORGANISM. 191 



still greater height (during a longer time) it perforates 

 the table ; its own motion is communicated to a certain 

 number of the particles of the wood which now fall 

 along with the stone itself. The stone, while at rest, 

 possessed none of these properties. 



The velocity of the falling body is always the effect 

 of the moving force, and is, ceteris paribus, propor- 

 tional to the force of gravitation. 



A body, falling freely, acquires at the end of one 

 second a velocity of 30 feet. The same body, if fall- 

 ing on the moon, would acquire in one second only a 

 velocity of s 3 B ths of a foot = 1 inch, because, in the 

 moon, the intensity of gravitation (the pressure acting 

 on the body, the moving power) is 360 times smaller. 



If the pressure continue uniform, the velocity is di- 

 rectly proportional to it ; so that, for example, the 

 body falling 360 times slower, will, after 360 seconds, 

 have the same velocity as the other body after one 

 second. 



Consequently the effect is proportional, not to the 

 moving force alone, nor to the time alone, but to the 

 pressure multiplied into the time, which is called the 

 momentum of force. 



In two equal masses the velocity expresses the mo- 

 mentum of force. But under the same pressure a body 

 moves more slowly as its mass is greater ; a mass twice 

 as great requires, in order to attain in the same time an 

 equal velocity, twice the pressure ; or, under the single 

 pressure, it must continue in motion twice as long. 



In order, therefore, to have an expression for the 



