128 On, Machines i?i General. 



with some reflections upon the fundamental laws from which 



I set out, in order to establish the theory which it contains. 



Reflections upon the fundamental Laws of Equilibrium and 

 of Movements. 

 Among the philosophers who have been occupied with 

 inquiries respecting the laws of movement, some make me- 

 chanics an experimental science, othens a science purely ra> 

 tional ; i. e. the. former, comparing the phsenomena of Na- 

 ture, decompose them, as it were, in order to know what 

 they possess in common with each other, and thus to re- 

 duce them to a small number of principal facts which serve 

 to explain all the others, and to prognosticate what should 

 happen in- every circumstance : the latter begin by hypo- 

 theses, then, reasoning consequently to their supposition^ 

 attain the discovery of the laws which bodies would pursue 

 in their movements, if their hypotheses were conformable to 

 Nature; then comparing their results with the phaenomena, 

 and finding that they agree, conclude that their own hypo- 

 thesis is exact, i. e. that bodies in fact follow the laws which 

 they had at first only supposed. 



The first of these two classes of philosophers set out 

 therefore in their researches from the primitive notions which 

 Nature has impressed upon us, and from experiments which 

 she continually presents to us : the second class set out from 

 definitions and hypotheses. With the former, the names 

 of bodies, of powers, of equilibrium, and of movement, 

 answer to first ideas ; they cannot nor should not define 

 them : the rest, on the contrary, having every thing to draw 

 from their own sources, are obliged to define these terms 

 with precision, and to explain all their suppositions clearly: 

 but if this method seems more elegant, it is also much more 

 difficult than the other; for there is nothing so perplexing 

 in most .of the rational sciences, and particularly in the one 

 under consideration, as to lay down at first precise-defi- 

 nitious, upon which no ambiguity remains : it would in- 

 volve me in metaphysical discussions far above my ability, 

 to investigate all those which have been hitherto proposed : I 

 shall content myself with examining the first and the most 

 simple. 



What 



