86 LECTUEES ON BIOLOGY 



of the first, and we now describe the first change as cause and 

 the second as effect. By conceiving the Law of Causality to 

 be necessary and universal we admit that it does not proceed 

 from experience, for experience can only give us probability and 

 comparative universality, but never necessity. 



Let us consider the atomistic theory. An atom of the above 

 has never been observed by any human eye, yet on the hypothesis 

 of the atom has been reared the proud edifice of modern chemistry 

 which owes to the atomistic theory its greatest successes. But 

 what precisely are atoms ? They are the ultimate particles, divis- 

 ible neither chemically nor physically, from which all elements are- 

 said to to be constructed. But indivisibility is inconceivable. 

 However minute we may conceive atoms to be, they always remain 

 bodies possessing all the properties of bodies volume, form, 

 weight, solidity, &c. But a body possessing volume and being 

 indivisible is in itself a contradiction. For if we persist in dividing 

 a body into more and more minute particles we shall finally arrive 

 at a point where mechanical divisibility seems no longer possible, 

 though the mind does not recognize a limit to the idea of divisi- 

 bility. We see, therefore, that even the doctrine of the atom is a 

 hypothesis which to a certain extent is in conflict with our con- 

 ceptions, yet it has achieved enormous advances in our knowledge. 

 But just as once the Ptolemaic system, though proceeding 

 from false premises, provided a satisfactory explanation for most 

 astral phenomena, and ruled science for thousands of years until 

 it was replaced by the more comprehensive system of Copernicus, 

 so it is conceivable that in future times scientific progress will 

 remove the bounds of the atomistic theory and substitute for it 

 a more comprehensive law. 



Without hypothesis there is no science, nor is there any justi- 

 fication for fighting shy of hypotheses. One might even be 

 tempted to say to the supporters of pure empirical research, who 

 seek in experience alone the ' last word of wisdom,' that it is 

 theory, not experience, which grants absolute certainty. How 

 often are we not deceived by our senses ? How often does not 

 experience desert us ? And even if according to Kant all our 

 perception begins with experience, it is not by any means all 

 knowledge that springs from experience. Hypothesis, however, 

 must not be carried to the limitless, but at every stage prove 

 its value by the results of experience and observation. 



