AUTHOR'S PREFACE. 



IN the late evening of an active life I offer to the German 

 public a work, whose undefined image has floated before my 

 mind for almost half a century. I have frequently looked 

 upon its completion as impracticable, but as often as I have 

 been disposed to relinquish the undertaking, I have again 

 although perhaps imprudently resumed the task. This work 

 I now present to my cotemporaries with a diffidence inspired 

 by a just mistrust of my own powers, while I would willingly 

 forget that writings long expected are usually received with 

 less indulgence. 



Although the outward relations of life, and an irresistible 

 impulse toward knowledge of various kinds, have led me to 

 occupy myself for many years and apparently exclusively 

 with separate branches of science, as, for instance, with de- 

 scriptive botany, geognosy, chemistry, astronomical determin- 

 ations of position, and terrestrial magnetism, in order that I 

 might the better prepare myself for the extensive travels in 

 which I was desirous of engaging, the actual object of my 

 studies has nevertheless been of a higher character. The 

 principal impulse by which I was directed was the earnest 

 endeavor to comprehend the phenomena of physical objects in 

 their general connection, and to represent nature as one great 

 whole, moved and animated by internal forces. My inter 

 course with highly-gifted men early led me to discover that, 

 without an earnest striving to attain to a knowledge of special 

 branches of study, all attempts to give a grand and general 

 view of the universe would be nothing more than a vain illu- 

 sion. These special departments in the great dorr^'M of nat 



