AND COLOUR-PERCEPTION BY F. W. EDRIDGE-GREEN, M.D., F.G.S. AUTHOR OF "MEMORY: ITS LOGICAL RELATIONS AND CULTIVATION," MEMBER OF THE INTERNATIONAL CODE OF SIGNALS COMMITTEE, ETC. WITH THREE COLOURED PLATES LONDON KEGAN PAUL, TRENCH, TRÜBNER & CO., LTD 1891 PREFACE. THE very favourable reception accorded to my book on Memory" and papers on "Colour-blindness" has in duced me to write this book for the benefit of those who may have to test for colour-blindness. The theory of colour-perception which I have advanced in this book is an application of the theory of psycho-physical perception, described in my book on Memory," to the phenomena of colour-blindness and colour-perception. This book is essentially practical. The observations are based on the careful examination of 116 colour-blind persons and of all the recorded cases to which I could obtain access. I should be glad to hear from any colourblind person concerning his views on colour, and the difficulties which he has encountered. I have obtained much valuable information from colour-blind persons relating to facts concerning their colour-perception which they have found inconsistent with the ordinarily accepted views. If the theory which I have given in this book be not true, it must be very closely allied to the truth, as all my theoretical predictions are verified by facts. In examining colour-blind persons, I avoided all leading questions, so that no bias should be given to them one way or the other. I have given a numerous series of cases which, even if the theory be not accepted, are definite facts of colour-blindness to which any future theory must conform. The practical portion of this book is the outcome of the work which I did at the request of the Board of Trade. I must here express my great indebtedness to the officials of the Marine Department of the Board of Trade, and especially to the late Mr. Gray, for the assistance which they have afforded me in making my investigations. Mr. Gray took the greatest interest in colour-blindness, and spared no trouble to obtain efficient tests. It seems remarkable to me that criticism has been almost confined to the colour-tests of the Board of Trade, whilst those used by the Navy and Railway companies, which are incomparably less efficient, have scarcely been noticed, |