CHAPTER XIII 

 SOME UNSOLVED SCIENTIFIC PROBLEMS 



IN the preceding chapters I have endeavored to out- 

 line the story of the achievements of our century in 

 the various fields of pure science. In so broad an at- 

 tempt, within such spacial limits, it has of course been 

 impossible to dwell upon details, or even to hint at 

 every minor discovery. At best one could but sum- 

 marize the broad sweep of progress somewhat as a bat- 

 tle might be described by a distant eye-witness, telling 

 of the general direction of action, of the movements 

 of large masses, the names of leaders of brigades and 

 divisions, but necessarily ignoring the lesser fluctuations 

 of advance or recession and the individual gallantry of 

 the rank and file. In particular, interest has centred 

 upon the storming of the various special strongholds of 

 ignorant or prejudiced opposition, which at last have 

 been triumphantly occupied by the band of progress. 

 In each case where such a stronghold has fallen, the 

 victory has been achieved solely through the destructive 

 agency of newly discovered or newly marshalled facts 

 the only weapons which the warrior of science seeks 

 or cares for. Facts must be marshalled, of course, 

 about the guidon of a hypothesis, but that guidon can 

 only lead on to victory if the facts themselves support 

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