vi PREFACE. 



sharply in the introduction, and to preserve it rigidly 

 throughout the work. This is, indeed, a case in which, 

 as Theodor Fechner has recently said, a definite deci- 

 sion has to be made between two fundamental alter- 

 natives. May our exposition afford a lucid testimony 

 to this dictum of one of the patriarchs of the philo- 

 sophical view of nature. 



Oscar Schmidt. 

 Strassbukg, October 18th, 1873. 



