It plainly discerns that the track along which the voyage of civilization has thus far been made, has been left; and that a new departure, on all unknown sea, has been taken.
Though deeply impressed with such thoughts, I should not have presumed to write this book, or to intrude on the public the ideas it presents, had I not made the facts with which it deals a subject of long and earnest meditation.

And I have gathered a strong incentive to undertake this duty from the circumstance that a "History of the Intellectual Development of Europe," published by me several years ago, which has passed through many editions in America, and has been reprinted in numerous European languages, English, French, German, Russian, Polish, Servian, etc., is everywhere received with favor.
In collecting and arranging the materials for the volumes I published under the title of "A History of the American Civil War," a work of very great labor, I had become accustomed to the comparison of conflicting statements, the adjustment of conflicting claims.

The approval with which that book has been received by the American public, a critical judge of the events considered, has inspired me with additional confidence.

I had also devoted much attention to the experimental investigation of natural phenomena, and had published many well-known memoirs on such subjects.

And perhaps no one can give himself to these pursuits, and spend a large part of his life in the public teaching of science, without partaking of that love of impartiality and truth which Philosophy incites.