This volume is the first of a series designed by the Author with the purpose of placing in the hands of the public, in more serviceable form, those portions of his earlier works which he thinks deserving of a permanent place in the system of his general teaching. They were at first intended to be accompanied by photographic reductions of the principal plates in the larger volumes; but this design has been modified by the Author's increasing desire to gather his past and present writings into a consistent body, illustrated by one series of plates, purchaseable in separate parts, and numbered consecutively.