INTRODUCTION. 



matter of this book. Where before there was solid, walk- 

 able ground to the older science, now there is nothing but 

 shifting sand. The last century began with the atom, and 

 the result is the implements of civilization as we have them. 

 This century begins with the atom within the atom, and, if 

 one may judge, the civilization of the coming years will be 

 rapidly modified and eventually transformed into phases of 

 which, now, we have but the barest glimpse. 



Since it has been the cardinal desire of the writer to make 

 this book a logical sequence and, to some extent, a synthesis 

 of this new knowledge, he has deemed it advisable to begin 

 with definitions which formulate the fundamental concep- 

 tions of the older science and to build the book up to the 

 definitions, re-defined, which sum up the advance. Only in 

 this way can the general reader obtain a reasonably com- 

 prehensive grasp of the subject-matter and only in this 

 way, also, can the writer force upon him an intellectual 

 conviction of its validity. 



Since there appears to be no text-book which even at- 

 tempts to cover this field of knowledge it is hoped that 

 this simple gathering together of its most significant facts 

 and theories may prove useful and helpful to the teacher 

 and the student. 



The progressive teacher, particularly in the high school 

 or smaller college, finds it, often, exceedingly difficult to 

 gain access to the original sources of knowledge. 



The student, whether he is now in school or college or 

 whether he has passed therefrom into his life-work of me- 

 chanical or professional activity, generally has not time for 

 and does not desire such original sources, though he may 

 have an eager wish to keep abreast of the march of knowl- 

 edge. 



Teachers and advanced students of branches of knowl- 



