vi PREFACE. 



It is impossible to write a book which is entirely free 

 from error, but I have done my best to make my lucubra- 

 tions accurate, and I commit them to the public, trusting 

 that my readers will look leniently on mistakes should they 

 find any. I can only say, may they prove to be few and 

 far between ; and in conclusion, let me remark that I have 

 had the assistance of my father, so that the work has had 

 the advantage of a double supervision. 



J. H. G., J UN. 



