NEWTON S PRINCIPIA. 305 



displaced, would not return to their former orbits. We 

 should, therefore, expect those planets which are furthest 

 from the sun to be the densest; but the contrary is the 

 case. Principia, prop, viii., book Hi., cor. 4. 



The planets that have satellites were supposed by Des 

 cartes to be the centres of smaller vortices ; but it has been 

 already shown, that every vortex continually grows larger 

 and larger, and thus every part of the fluid will be agitated 

 with a motion resulting from the action of all the globes. 

 Therefore the vortices will not be confined to any certain 

 limits, but by degrees will run mutually into each other, 

 and by the mutual action of the vortices on each other the 

 globes will be perpetually moved from, their places. They 

 cannot possibly keep any certain positions among them 

 selves unless some force restrains them. Forces are ne~ 

 cessary, therefore, not only to keep the globes turning, but 

 also to keep them in their places. 



