On Sal Nitrum and Nitro- Aerial Spirit 6i 



matter ? But with a view to a further conjecture on 

 this extremely recondite subject I think it should first 

 be maintained in regard to motion in general that it 

 can be produced in no other way than by impulse. 

 For as regards a natural inclination of inanimate things 

 by which (in popular belief) they begin this or that 

 movement spontaneously, I simply cannot understand 

 it. For I do not know how an elective movement of 

 that kind can exist without intelligence or at least 

 sensation. Our opinion indeed is that inanimate 

 things have no inclination, but that instead of it there 

 is that power merely by which every thing remains 

 always as far as may be in the same state. But a 

 power of this kind implies nothing more than that 

 inanimate things are unable to dispose of themselves 

 or to alter their state, but are altogether dependent 

 upon other things. Whenever then a body is at rest 

 nothing else can be imagined than that it will remain 

 for ever in a state of rest, unless as the ingenious 

 Descartes has remarked a force is introduced from 

 some other thing. Wherefore elasticity and gravity 

 from which spontaneous movements, as they are 

 usually called, arise, must be supposed to be due to 

 impact of something invisible. But since such things 

 as are possessed of elastic force and gravity are always 

 ready to move, provided there is nothing to hinder 

 their motion, it seems that we should certainly con- 

 clude that there is some kind of matter which being in 

 constant agitation always strikes the said things in its 

 motion and tries to move them. It is long since 

 Descartes drew attention to such perpetually moving 

 matter, and indeed there can be no doubt whatever 

 regarding its existence. For I cannot conceive how 

 sound, and light, and the like, are propagated where 

 there is no air unless there exists some fine matter by 



