Preface xxxiii 



* Life has unfathomable secrets. Human 

 knowledge will be erased from the archives of 

 the world before we possess the last word that 

 the Gnat has to say to us. . . . 



' Success is for the loud talkers, the self- 

 convinced dogmatists ; everything is admitted 

 on condition that it be noisily proclaimed. Let 

 us throw off this sham and recognize that, in 

 reality, we know nothing about anything, if 

 things were probed to the bottom. Scientifi- 

 cally, Nature is a riddle without a definite solu- 

 tion to satisfy man's curiosity. Hypothesis 

 follows on hypothesis ; the theoretical rubbish- 

 heap accumulates ; and truth ever eludes us. 

 To know how not to know might well be the 

 last word of wisdom.' 



Evidently, this is hoping too little. In the 

 frightful pit, in the bottomless funnel wherein 

 whirl all those contradictory facts which are 

 resolved in obscurity, we know just as much 

 as our cave-dwelling ancestors ; but at least 

 we know that we do not know. We survey 

 the dark faces of all the riddles, we try to 

 estimate their number, to classify their vary- 



