As one or two questions, asked of me since the publication of this work,
have indicated points requiring elucidation, I have added a few short
notes in the first Appendix. It is not, I think, desirable otherwise to
modify the form or add to the matter of a book as it passes through
successive editions; I have, therefore, only mended the wording of some
obscure sentences; with which exception the text remains, and will
remain, in its original form, which I had carefully considered. Should
the public find the book useful, and call for further editions of it,
such additional notes as may be necessary will be always placed in the
first Appendix, where they can be at once referred to, in any library,
by the possessors of the earlier editions; and I will take care they
shall not be numerous.
_August 3, 1857._