ILLUSIONS

A PSYCHOLOGICAL STUDY

BY

JAMES SULLY

AUTHOR OF "SENSATION AND INTUITION," "PESSIMISM," ETC.

THIRD EDITION

LONDON
KEGAN PAUL, TRENCH & CO., 1, PATERNOSTER SQUARE
1887

(The rights of translation and of reproduction are reserved)

THE INTERNATIONAL SCIENTIFIC SERIES.

VOL. XXXIV.

PREFACE.

The present volume takes a wide survey of the field of error, embracing in its view not only the illusions of sense dealt with in treatises on physiological optics, etc., but also other errors familiarly known as illusions, and resembling the former in their structure and mode of origin. I have throughout endeavoured to keep to a strictly scientific treatment, that is to say, the description and classification of acknowledged errors, and the explanation of these by a reference to their psychical and physical conditions. At the same time, I was not able, at the close of my exposition, to avoid pointing out how the psychology leads on to the philosophy of the subject. Some of the chapters were first roughly sketched out in articles published in magazines and reviews; but these have been not only greatly enlarged, but, to a considerable extent, rewritten.

J. S.

Hampstead, April, 1881.

CONTENTS.

CHAPTER I.

THE STUDY OF ILLUSION.

Vulgar idea of Illusion, 1, 2; Psychological treatment of subject, 3, 4;
definition of Illusion, 4-7; Philosophic extension of idea, 7, 8.


CHAPTER II.

THE CLASSIFICATION OF ILLUSIONS.

Popular and Scientific conceptions of Mind, 9, 10; Illusion and
Hallucination, 11-13; varieties of Immediate Knowledge, 13-16; four-fold
division of Illusions, 16-18.


CHAPTER III.

ILLUSIONS OF PERCEPTION: GENERAL.

Psychology of Perception:—The Psychological analysis of Perception, 19,
20; Sensation and its discrimination, etc., 20, 21; interpretation of
Sensation, 22, 23; construction of material object, 23, 24; recognition
of object, specific and individual, 24-27; Preperception and
Perception, 27-31; Physiological conditions of Perception, 31-33;
Visual and other Sense-perception, 33, 34.

Illusions of Perception:—Illusion of Perception defined, 35-38; sources
of Sense-illusion,