(From the second edition, 1869)

It is a pleasant reflection that twenty years of added experience and extended research have not materially changed the views at first expressed. The careful reexamination which we have been required to make in the preparation of the present enlarged statement, leaves not a doubt in our mind of the substantial correctness of the doctrines herein set forth. The first writing was undertaken under the inspiration, and conducted during the evolution, of an exalted experience, and amid the glow of intense zeal. The present writing is the fruit of calm study and mature and deliberate judgment. We are not aware that a single point has been relinquished or materially modified.