78 THE LIMITATIONS OF SCIENCE 



variations in it for the bodies themselves. As explana- 

 tions of phenomena both ideas are occult, but not to 

 the same degree. We know, for a fact, that there is 

 an attractive force between bodies of sensible size, 

 although we cannot explain its cause, and we can 

 in our imaginations transfer a like form to bodies of 

 an insensible size with some probability of truth. But 

 the postulation of a plenum of continuous substance and 

 of variations in it, which affect us as matter, is wholly 

 occult since we have no experience from sensible mat- 

 ter to guide us ; in fact, both plenum and its variations 

 always have characteristics assigned to them directly 

 contrary to the evidence of our senses. 



The history of scientific theory is a record of the 

 conflict between these rival ideas of continuity and dis- 

 continuity of substance. While the atomistic school 

 has frequently had the advantage, since the time of 

 Descartes the doctrine of the continuity of matter has 

 persisted in some form, and at the present time is 

 again established as the basis of physical theory. 

 Nevertheless, the cosmical system as deduced by Des- 

 cartes from this hypothesis of a plenum has suffered 

 shipwreck and comparatively few think it profitable to 

 study it in detail. Before we adopt his principles and 

 discard his conclusions, it is at least advisable to see 

 whether his errors lie in the principles themselves or 

 in the inability of Descartes to derive true conclusions 

 from correct principles. Fortunately, we have in the 



