PREFACE 



IN the following pages I have endeavored to give a sim- 

 ple account of problems which have occupied the attention 

 of the human mind ever since the dawn of civilization, and 

 which can never lose their interest until time shall be no 

 more. While to most persons these subjects will have but 

 an historical interest, yet even from this point of view they 

 are of more value than the history of empires, for they are 

 the intellectual battlefields upon which much of our prog- 

 ress in science has been won. To a few, however, some of 

 them may be of actual practical importance, for although 

 the schoolmaster has been abroad for these many years, it 

 is an unfortunate fact that the circle-squarer and the per- 

 petual-motion-seeker have not ceased out of the land. 



In these days of almost miraculous progress it is difficult 

 to realize that there may be such a thing as a scientific im- 

 possibility. I have therefore endeavored to point out 

 where the line must be drawn, and by way of illustration 

 I have added a few curious paradoxes and marvels, some 

 of which show apparent contradictions to known laws of 

 nature, but which are all simply and easily explained when 

 we understand the fundamental principles which govern each 

 case. 



In presenting the various subjects which are here dis- 

 cussed, I have endeavored to use the simplest language 

 and to avoid entirely the use of mathematical formulae, for 



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