70 LIFE AND DEATH. 



which are, in a measure, logical elements, to which 

 may be joined a third element, itself experimental, 

 having its foundations in our sensations — namely, 

 force, zvork, ox poiver. 



The ideas of force, work, and power, are drawn from 

 the experience man has of his muscular activity. 

 Nevertheless the greatest mathematical minds from 

 from Descartes to Leibniz have been obliged to define 

 and explain them clearly. 



Force. — The prototype of force is weight, universal 

 attraction. Experiment shows us that every body 

 falls as long as no obstacle opposes its fall. This is 

 so universal a property of matter that it serves to 

 define it. The force, weight, is therefore the name 

 given to the cause of the fall of the bodies. 



Force in general is the cause of motion. Hence 

 force exists only in so far as there is motion. There 

 would be no force without action. This is Newton's 

 point of view. It did not prevail, and was not the 

 point of view of his successors. The name of force 

 has been given not only to the cause which produces 

 or modifies motion, but to the cause which resists and 

 prevents it. And then not only have forces in action 

 been considered (dynamics), hvX forces at r^j/ (statics). 

 Now, to Newton there was no statics. Forces do not 

 continue to exist when they produce no motion ; they 

 are not in equilibrium, they are destroyed. 



The idea of force therefore is a metaphysical idea 

 which contains the idea of cause. But it becomes 

 experimental immediately it is looked upon as resist- 

 ing motion, according to the point of view of Newton's 

 opponents. Its foundations lie in the muscular 

 activity of man. 



Man can support a burden without bending or 



