INFLUENCE ON RECENT SCIENCE 85 



These postulates of Descartes, that space is a plenum 

 and motion the result of an impact, required him to 

 oppose such theorists as Gassendi who were advocat- 

 ing the atomic theory and an occult attractive force in 

 matter as its cause of motion. It thus became of prime 

 importance for him to formulate laws of impact and 

 motion. This was an extremely difficult problem, espe- 

 cially so as the available knowledge of the phenomena 

 of impact and motion was very deficient and, such 

 as it was, indicated that friction produced an uncom- 

 pensated diminution of velocity. With great care and 

 in minute detail, he announced such laws as would, in 

 his opinion, maintain constant the total quantity of 

 motion or momentum of the universe in spite of fric- 

 tion. That is, such laws as would transfer the loss of 

 motion of one body by impact to an equivalent increase 

 of another. These laws are: 



God in his omnipotence created matter with motion 

 and rest. 



If a body move twice as fast as another twice as 

 great, the quantity of motion of the two is the 

 same. 



All bodies, which move, tend to move in straight 

 lines and can change their direction only by encounter- 

 ing others. 



If a moving body strike another of greater mo- 

 mentum (plus fort) than itself, it loses none of its 

 motion and if it strikes another with a less momentum 



