104 THE LIMITATIONS OF SCIENCE 



this sort should always be announced as soon as a con- 

 siderable number of facts point to its probable truth; 

 such tentative laws always direct attention to the phe- 

 nomena involved and stimulate research. 



But hypothesis in the other sense does not gradually 

 crystallize into law as our knowledge increases. No 

 information, however greater than ours at present, 

 will ever advance Descartes's hypothesis a step closer 

 to a law. We shall never have any data about his 

 three kinds of matter, his nature of free space, etc.; we 

 learn constantly more about the action of light but 

 we still drift confusedly and without a guide between 

 his apparatus of pressures, Newton's corpuscles, and 

 Huygens's waves; the latest treatise on optics now 

 states that we may have to mix together all three of 

 them. 



The system of Descartes will fascinate anyone who 

 surrenders himself to its spirit and scope, but illusion 

 is not the function of science. Nor can I find any more 

 accurate and just criticism of this and all other 

 hypotheses than that given by Bolingbroke : " The 

 notion Descartes entertained and propagated, that there 

 is, besides clear ideas, a kind of inward sentiment of 

 evidence, which may be a principle of knowledge, is, 

 I suppose, dangerous in physical inquiries as well as 

 in abstract reasoning. He who departs from the 

 analytic method, to establish general propositions con- 

 cerning the phenomena on assumptions, and who rea- 



