442 



-SCIENCE. 



[N. S. Vol. XIV. No. 351. 



and now closed, and could, at the most, 

 work only under immutable conditions to 

 which the living and dead must alike sub- 

 mit. On the contrary, their vital force 

 pervaded the organism in all its parts. It 

 was an active and energetic opponent of 

 the laws of physics and chemistry. It 

 maintained its own existence not by obey- 

 ing but by defying them ; and though 

 destined to be linally overcome in the sepa- 

 rate campaigns of which each individual 

 living creature is the scene, yet like some 

 guerilla chieftain it was defeated here only 

 to reappear there with unabated confidence 

 and apparently undiminished force. 



This attitude of mind checked the ad- 

 vance of knowledge. Difficulty could be 

 evaded by a verbal formula of explanation 

 which in fact explained nothing. If the 

 mechanical, or physical, or chemical causes 

 of a phenomenon did not lie obviously upon 

 the surface, the investigator was tempted 

 to forego the toil of searching for them 

 below ; it was easier to say that the vital 

 force was the cause of the discrepancy, and 

 that it was hopeless to attempt to account 

 for the action of a principle which was in- 

 comprehensible in its nature. 



For the physicist the danger is no less 

 serious though it lies in a somewhat differ- 

 ent direction. At present he is checked in 

 his theories by the necessity of making 

 them agree with a comparatively small 

 number of fundamental hypotheses. If 

 this check were removed his fancy might 

 run riot in the wildest speculations, which 

 would be held to be legitimate if only they 

 led to formulae in harmony with facts. 

 But the very habit of regarding the end as 

 everything, and the means by which it was 

 attained as unimportant, would prevent the 

 discovery of those fragments of truth which 

 can only be uncovered by the painful proc- 

 ess of trying to make inconsistent theories 

 agree, and using all facts, however remote, 

 as the tests of our central generalizatiou. 



"Science," said Helmholtz, ''Science, 

 whose very object it is to comprehend Na- 

 ture, must start with the assumption that 

 Nature is comprehensible." And again: 

 " The first principle of the investigator of 

 Nature is to assume that Nature is intel- 

 ligible 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 deny that in 

 living matter something may be hidden 

 which neither physics nor chemistry can 

 explain, but they assert that the action of 

 physical and chemical forces in living 

 bodies can never be understood, if at every 

 difficulty and at every check in our inves- 

 tigations we desist from further attempts in 

 the belief that the laws of physics and 

 chemistry have been interfered with by an 

 incomprehensible 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 con- 

 tented 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 ex- 

 periment, we can avoid the acceptance of 

 these absurdities. Something will have 

 been gained if the more obvious difficulties 

 are removed, even if we have to admit that 

 in the background there is much that we 

 cannot grasp. 



THE LIMITS OF PHYSICAL THEORIES. 



And this brings me to my last point. It 

 is a mistake to treat physical theories in 

 general, and the atomic theory in particu- 

 lar, as though they were parts of a scheme 



