HE first edition underwent many vicissitudes.

had a phenomenal sale-over 20,000 copies the publishers said. More than half the book appeared with a few changes of phraseology, but entirely uncredited, as a small book on psychology by a school principal. A translation into Mandarin Chinese was prepared by Prof. Headland, of Peking University, but the buildings of the university were burned during the Boxer outbreak in 1900, and both manuscript and plates were lost.

The first edition was exhausted and a second was called for in 1900. In spite of a promise to furnish the revision promptly I have been hindered from doing it by scientific work and other duties. I feel that I owe an earnest apology to persons who have. been seeking copies of the book and to the publishers who have waited with patience and courtesy.

It is quite impossible to give credit to all to whom it is due. The references to the investigators who have built up the new psychology may be found in more technical works, such as those of Wundt; full literature is given in Titchener's laboratory manuals and in Baldwin's Dictionary of Philosophy. Where the material of this volume has not been drawn from other investigators, it is the work of myself and my pupils in the Yale Psychological Laboratory. Figure 13 is from an

investigation by McAllister; 24, 30, 57, 79, 80, 177, 180, from Gilbert; 31-33 from Marey; 42 from Miyake; 45 from Bliss; 50-55 from Hensen; 59-62 from Féré; 78, 81, 166-171 from Wundt; 105 from Kirschmann; 138 -141, 148-156 from Martius-Matzdorff; 157-164 from an art catalogue; 165 from Witmer; and 176 from Wolfe. The figures for the optical illusions have been so frequently repeated that it seems impossible to assign credit.

Vanderbilt Clinic, Columbia University,

October, 1907.

A

PREFACE TO THE FIRST EDITION

FELLOW psychologist said to me one day, "Are

you not afraid that all this accurate and fine work in the laboratory will scare away the public?" We all belong to the great public except in regard to the particular handiwork, trade, or science that each knows something about. And yet we are all interested in hearing about a new science. There is nothing too good for the public-the finer the work, the more novel the invention, or the more important the discovery, the greater the duty of telling it to the public in language that can be understood. This is the first book on the new, or experimental, psychology written in the English language.

Yale University, Jan., 1895.