iv PREFACE. 



Including this time, they are the result of 

 fourteen years' close attention to a subject 

 which always had a peculiar interest with the 

 author. 



There being no text-book or guide on the 

 subject, so far as the author is aware, he feels 

 that, though no longer in the profession, he 

 has contracted an obligation to impart to others 

 that which dearly-bought experience has taught 

 him ; and his end will have been answered if, 

 with the help of these pages, young practi- 

 tioners learn the subject at an easier rate 

 than he did. 



It is also humbly hoped that these pages 

 may be of some use to those whose years and 

 maturity have secured them that confidence in 

 their skill which is the laudable ambition of all. 



W. F. 



London, ist Jan., 1878. 



