196 PHYSIOLOGICAL BOTANY. 



greater height (during a longer time), it perforates the 

 table ; its own motion is communicated to a certain num- 

 ber 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, c&teris 

 paribus, proportional to the attraction of gravitation. A 

 body falling freely acquires, at the end of one second, a 

 velocity of 30 feet. The same body, if falling on the 

 moon, would acquire, in one second, only a velocity of 

 sloths of a foot, = 0*1 inch, because in the moon, the 

 intensity of gravitation (the pressure acting on the body, 

 the moving power) is 3600 times less." 



We shall not dwell upon the individual expressions 

 which are not always accurately applied, but shall merely 

 ask, Why does Liebig omit to notice the law of inertia, 

 upon which all mechanical determinations are based, 

 which causes the velocity of a falling body to increase 

 constantly in proportion to the duration of its fall. Galileo 

 applied it without recognising it ; when he discovered 

 the law, that the space through which a body falls is as 

 the square of the time in which it falls. Newton called 

 it the law of inertia, placed it at the head of his ' Principia 

 Philosophise Naturalis Mathematica/ and expressed it as 

 follows : " A body continues in its state of rest or motion, 

 in the same direction and with the same velocity, until 

 some motive force compels it to change this state." It 

 may be perhaps attributed to the physio-philosophers 

 of Germany that they have forgotten, or at least over- 

 looked, this law in the explanation of natural phenomena ; 

 in fact, that natural philosophers, who, like Liebig, have 

 no respect for philosophy, make no mention of this law. 

 Not only does it explain the increased velocity acquired 

 by a falling body, but even the most common, the daily 

 phenomena occurring upon the moving globe, could not 

 be explained without it such, e. g. as the fall of a stone 

 from a house or a tower; why, when allowed to fall 

 from the west side of a house it does not reach the earth 



