TRANSLATOR'S PREFACE. 



IN presenting this excellent little work, with the 

 permission of the author, to the English-reading 

 public, scarcely anything remains to be added to what 

 Dr. Lob has already said in his prefaces to the German 

 and American editions. He has read the manu- 

 script and made the necessary changes and additions 

 so as to have it correspond to the second German 

 edition which is about to appear. 



The translator has adhered as closely as possible to 

 the original text. He has made some additions and 

 added a table of contents and a complete index, which 

 he thinks will enhance the value of the book. 



To Dr. B. B. Boltwood of the Sheffield Scientific 

 School of Yale University, who has had the kind- 

 ness to revise the manuscript, grateful acknowledg- 

 ments are due for his painstaking and valuable 

 services. 



SPRINGFIELD, OHIO, 

 November, 1898. 



