A MODEL OF NATURE. 191 



of scientific theory too often assume that there is no alternative 

 between the opposing assertions that atoms and the ether are mere 

 figments of the scientific imagination, or that, on the other hand, a 

 mechanical theory of the atoms and of the ether, which is now con- 

 fessedly imperfect, would, if it could be perfected, give us a full and 

 adequate representation of the underlying realities. 



For my own part 1 l)elieve that there is a via media. 



A man peering into a darkened room, and describing what he thinks 

 he sees, may l^e right as to the general outline of the objects he dis- 

 cerns, wrong as to their nature and their precise forms. In his descrip- 

 tion fact and fanc}' may be blended, and it may be difficult to say 

 where the one ends and the other begins; but even the fancies will not 

 be worthless if tlic}^ are based on a fragment of truth, which will pre- 

 vent the explorer from walking into a looking-glass or stumbling over 

 the furniture. He who saw "men as trees walking" had at least a per- 

 ception of the fundamental fact that something was in motion around 

 him. 



And so, at the beginning of the twentieth century, we are neither 

 forced to abandon the cliiim t<> have penetrated below the surface of 

 nature, nor have we, with all our searching, torn the veil of mystery 

 from the world around us. 



The range of our speculations is limited l)otli in space and time; in 

 space, for we have no right to claim, as is sometimes done, a knowl- 

 edge of the ''infinite universe;" in time, for the cumulative effects of 

 actions which might pass undetected in the short span of j^ears of 

 which we have knowledge, may, if continued long enough, modify our 

 most profound generalizations. If some such theory as the vortex- 

 atom theory were true, the faintest trace of viscositj'in the primordial 

 medium would ultimately destroy matter of every kind. It is thus a 

 duty to state what we l)elieve we know in the most cautious terms, but 

 it is ecpially a duty not to yield to mere vague doubts as to whether 

 we can know anything. 



If no other conception of matter is possible than that it consists of 

 distinct physical units — and no other conception has been formulated 

 which does not l)lur what are otherwise clear and definite outlines — if 

 it is certain, as it is, that vibrations travel through space which can 

 not be propagated ))y matter, the two foundations of physical theory 

 are well and truly laid. It ma}^ be granted that we have not yet 

 framed a consistent image either of the nature of the atoms or of the 

 ether in which they exist; but I have tried to show that in spite of the 

 tentative nature of some of our theories, in spite of many outstanding 

 difficulties, the atomic theor}^ unifies so many facts, simplifies so much 

 that is complicated, that we have a right to insist — at all events till an 

 equally intelligible rival hy[)othesis is produced — that the mai?i struc- 

 ture of our theory is true; that atoms are not merely helps to puzzled 

 mathematicians, but physical realities. 



