I. AW; ITS DEFINITIONS. 121 



parts, without organs — absolutely without visible 

 structure of any kind. In this jelly, nevertheless, 

 there works a "vital Force" capable of building 

 up an Organism of most complicated and perfect 

 symmetry. 



But what is a vital Force ? It is something 

 which w r e cannot see, but of whose existence we 

 are as certain as we are of its visible effects — nay, 

 which our reason tells us precedes and is superior 

 to these. We often speak of Material Forces as if 

 we could identify any kind of Force with Matter. 

 But this is only one of the many ambiguities of 

 language. All that we mean by a Material Force 

 is a force which acts upon Matter, and produces in 

 matter its own appropriate effects. We must go 

 a step farther therefore and ask ourselves, What 

 is Force ? What is our conception of it ? What 

 idea can we form, for example, of the real na- 

 ture of that force, the measure of whose opera- 

 tion has been so exactly ascertained — the Force 

 of Gravitation ? It is invisible — imponderable — 

 all our words for it are but circumlocutions to 

 express its phenomena or effects. 



There are many kinds of force in Nature — which 



