PREFATORY NOTE.
The following pages were written originally for the Encyclopædia Britannica, but had to be very much abridged in order to bring them within the limits of space the Editor could afford to devote to their subject. He did me the honor to express the opinion that their publication in extenso would prove of service to various classes of readers; and the Publishers of the "Encyclopædia" were so good as to urge me to adopt his suggestion. This book is the result.
I think it right to prefix this explanation; for the plan and execution might have been somewhat different had an independent volume been in contemplation from the first.
Edinburgh,
- 1st October 1886.
