vi PREFACE, 
We have, therefore, endeavoured to define our standpoint 
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. 
STRASBURG, October 18th, 1873. 
Oscar SCHMIDT, 
