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PREFACE 



AT this time of stress and anxiety we all, however 

 steadfast in giving our service to the great task in 

 which our country is engaged, must, from time to time, 

 seek intervals of release from the torrent of thoughts 

 which is set going by the tremendous fact that we are 

 fighting for our existence. To very many relief comes 

 in splendid self-sacrificing action, in the joyful exercise 

 of youthful strength and vigour for a noble cause. But 

 even these, as well as those who are less fortunate, need 

 intervals of diversion brief change of thought and mental 

 occupation after which they may return to their great 

 duties rested and refreshed. 



I know that there are many who find a never-failing 

 source of happiness in acquaintance with things belonging 

 to that vast area of Nature which is beyond and apart 

 from human misery, an area unseen and unsuspected by 

 most of us and yet teeming with things of exquisite 

 beauty ; an area capable of yielding to man knowledge 

 of inestimable value. Many are apt to think that 

 the value of " Science " is to be measured mainly if 

 not exclusively, by the actual power which it has 



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