84 THE LIMITATIONS OF SCIENCE 



tion and motion of a body we must use some other body 

 as a point of reference. But in this system, all space is 

 capable of motion and, in fact, is in rapid motion, and 

 with no possible stationary reference point all positions 

 and motions are merely relative. This question of abso- 

 lute motion has been the subject of much discussion in 

 the last few years, as certain phenomena of light re- 

 quire that, granting a luminiferous ether, it must be 

 absolutely stationary. And experiments have been de- 

 vised to determine whether we can measure the absolute 

 velocity of matter with respect to the ether. As in all 

 experiments involving the ether, the results are 

 nugatory. 



Nor, in the theory of Descartes, can there be action 

 at a distance, for matter is continuous and all motion 

 is the result of a push or impact. Motion, therefore, 

 he defines as the transference of a part of matter or of 

 a body from the neighborhood of those which touch it 

 immediately, and which we consider at rest, to the 

 neighborhood of others. And since all space is full 

 of matter, or rather is matter, each body is so fashioned 

 that it can never occupy a greater or a less space, nor 

 can any other body occupy the space while it is there; 

 therefore if a body move to another position, it must 

 displace an occupant; and this, another; so that every 

 motion results in a closed ring of moved bodies, each 

 finally occupying the space left by its previous occu- 

 pant. 



