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, Jun. 
