100 A MODEL OF NATURE. 



to he legitimate if only they led to fonmiUe in harmon}- with facts. 

 But the veiy habit of regarding the end as everything, and the means 

 by which it was attained as unimportant, would pi'event the discovery 

 of those fragments of truth which can only be uncovered by the pain- 

 ful process of trying to make inconsistent theories agree, and using 

 all facts, however remote, as the tests of our central generalization. 



"Science," said Helmholtz, "Science, whose very object it is to 

 comprehend Nature, must start with the assumption that Nature is 

 comprehensible.'" And again, "The tirst principle of the investigator 

 of Nature is to assume that Nature is intelligible to us, since otherwise 

 it would be foolish to attempt the investigation at all." These axioms 

 do not assume that all the secrets of the universe will ultimately be 

 laid bare, but that a search for them is hopeless if we undertake the 

 quest with the conviction that it will be in vain. As applied to life 

 they do not deu}' that in living matter something may be hidden which 

 neither ph^'sics nor chemistry can explain; l)ut they assert that the 

 action of ph3^sicaI and chemical forces in living bodies can never be 

 understood if at ever}' difficulty and at every check in our investiga- 

 tions we desist from further attempts in the belief that the laws of 

 ph^^sics and chemistry have been interfered with by an incomprehen- 

 sible vital force. As applied to physics and chemistry they do not 

 mean that all the phenomena of life and death will ultimately be 

 included in some simple and self-sufficing mechanical theory; they do 

 mean that we are not to sit down contented with paradoxes such as 

 that the same thing can fill both a large space and a little one; that 

 matter can act where it is not, and the like, if by some reasonable 

 hypothesis, capable of being tested by experiment, we can avoid the 

 acceptance of these absurdities. Something will have ])een gained if 

 the more obvious difficulties are removed, even if we have to admit 

 that in the background there is much that we can not grasp. 



THE LIMITS OF PHYSICAL THEORIES. 



And this })rings me to lu}' last point. It is a mistake to treat phys- 

 ical theories in general, and the atomic theory in particular, as though 

 they were parts of a scheme which has failed if it leaves anything 

 unexplained, which must be carried on indefinitely on exactly the same 

 principles, whether the ultimate results are or are not repugnant to 

 common sense. 



Physical theories begin at the surface with phenomena which directly 

 affect our senses. ' When they are used in the attempt to penetrate 

 deeper into the secrets of nature, it is more than probable that they 

 will meet with insuperable barriers; but this fact does not demonstrate 

 that the fundamental assumptions are false, and the question as to 

 whether any particular obstacle will be forever insuperable can rarely 

 be answered with certainty. 



Those who belittle the ideas which have of late governed the advance 



