Professor of Chemistry and Physiology in the University of New York; Author of a
"Treatise on Human Physiology," &c., &c.

NEW YORK:

HARPER & BROTHERS, PUBLISHERS,

FRANKLIN SQUARE.

186 3.

Entered, according to Act of Congress, in the year one thousand eight hundred and sixty-two, by

HARPER & BROTHERS,

In the Clerk's Office of the District Court of the Southern District of

New York.

PREFACE.

AT the meeting of the British Association for the Advancement of Science, held at Oxford in 1860, I read an abstract of the physiological argument contained in this work respecting the mental progress of Europe, reserving the historical evidence for subsequent publication.

This volume contains that evidence. It is intended as the completion of my work on Human Physiology, in which man was treated of as an individual. In this he is considered in his social relation.

But the reader will also find, I think, that it is a history of the prog. ress of ideas and opinions from a point of view heretofore almost entirely neglected. There are two methods of dealing with philosophical questions-the literary and the scientific. Many things which in a purely literary treatment of the subject remain in the background, spontaneously assume a more striking position when their scientific relations are considered. It is the latter method that I have used.

Social advancement is as completely under the control of natural law as is bodily growth. The life of an individual is a miniature of the life of a nation. These propositions it is the special object of this book to demonstrate.

No one, I believe, has hitherto undertaken the labor of arranging the evidence offered by the intellectual history of Europe in accordance with physiological principles, so as to illustrate the orderly progress of civilization, or collected the facts furnished by other branches of science with a view of enabling us to recognize clearly the conditions under which that progress takes place. This philosophical deficiency I have endeavored in the following pages to supply.

Seen thus through the medium of physiology, history presents a new aspect to us. We gain a more just and thorough appreciation of the thoughts and motives of men in successive ages of the world.

In the Preface to the second edition of my Physiology, published in 1858, it was mentioned that this work was at that time written. The