INTRODUCTION TO THE SIXTH EDITION. 



The department of the Physical Geography of the Sea is a new- 

 field of research ; there is great activity in it, and it is the aim of 

 the author of this work to keep its readers posted up with the im- 

 provements, the developments, and the contributions that are made 

 in this interesting field from time to time. 



The present edition contains much that is new; for the fifth 

 edition has been most carefully revised, much of it has been re- 

 cast, and some parts omitted. 



The desire is, that this work shall keep pace with the progress 

 of research. As it may be supposed, facts are sometimes misin- 

 terpreted or not understood when first developed. Whenever sub- 

 sequent research shows such to have been the case, I have not 

 hesitated to tear down whatever of conjecture or theory may have 

 been built on unstable foundations, and to reconstruct according 

 to the best lights. 



It is proper to say that, in accounting for the various phenome- 

 na that present themselves, I am wedded to no theories, and do not 

 advocate the doctrines of any particular school. Truth is my ob- 

 ject. Therefore, when the explanation which I may have at any 

 time offered touching any facts fails to satisfy farther developments, 

 it is given up the moment one is suggested which will account for 

 the new, and equally as well for the old system of facts. In every 

 instance that theory is preferred which is reconcilable with the 

 greatest number of known facts. The chapter of the Gulf Stream 

 has been enriched with the results of recent investigation, and the 

 theory of it farther developed. So also that on the Salts of the 

 Sea ; the Open Sea in the Arctic Ocean ; the Basin of the Atlan- 

 tic, and several others, but these especially have been greatly im- 

 proved. 



