To their Royal Highnesses, the Grand-duke and the Grand- 

 duchess of Saxony, the author expresses his thanks for their 

 interest and for the great honor of their presence at one of the 

 lectures. He has pleasure in thanking also their Excellencies, 

 the Ministers of Education of Saxe-Weimar-Eisenach, 

 Altenburg and Meiningen, his Magnificency the Prorektor, 

 the Curator of the University and his Colleagues for their 

 encouragement and hospitahty, by which the visit to Jena was 

 made very dehghtful. 



The lectures were written and have already been published 

 in German by Gustav Fischer in Jena. Professor von Bar- 

 deleben had the great kindness to revise the original manu- 

 script. The translation has been prepared by the author and 

 follows the original closely, though now and then a phrase 

 has been rendered freely. 



Charles S. Minot. 



Boston. 



