PREFACE TO THE SECOND AND THIRD EDITIONS. Xlll 



" The development of a physiological idea is the object of 

 the entire treatise ; men were fonder at that time than they 

 would now be of such semi-poetic clothing of severe scientific 

 truths/' 



In my eightieth year, I am still enabled to enjoy the 

 satisfaction of completing a third edition of my work, re- 

 moulding it entirely afresh to meet the requirements of the 

 present time. Almost all the scientific Elucidations or 

 Annotations have been either enlarged or replaced by new 

 and more comprehensive ones. I have hoped that these 

 volumes might tend to inspire and cherish a love for the 

 study of Nature, by bringing together in a small space the 

 results of careful observation on the most varied subjects ; 

 by showing the importance of exact numerical data, and the 

 use to be made of them by well-considered arrangement and 

 comparison ; and by opposing the dogmatic half-knowledge 

 and arrogant scepticism which have long too much prevailed 

 in what are called the higher circles of society. 



The expedition made by Ehrenberg, Gustav Hose, and 

 myself, by the command of the Emperor of Kussia, in 1829, 

 to Northern Asia (in the Ural and Altai mountains, and on 



