PEEFACE. 



THIS book was commenced some years ago, and 

 was to have 'been a joint production of my 

 colleague Mr J. L. Warren and myself. His 

 lamented and early death, due principally to his 

 over-zeal in the discharge of his public duties, 

 prevented the original plan from being carried 

 out ; it therefore devolved on me to complete 

 it alone, and since then much matter has been 

 collected, with which I have incorporated papers 

 that have appeared in different scientific maga- 

 zines and publications, on branches of the subject, 

 but at the same time the original style has been 

 adhered to, as if the joint- authorship still con- 

 tinued. This has been found necessary, as other- 

 wise the credit for the matter and facts collected 

 by Mr Warren, would be appropriated by me. 



