REVIEWS 177 



chiefly from photographs, while the type is of a strikingly clear full-face kind that 

 one would like to see more extensively employed. 



F. Cavers. 



MEDICINE 



An Introduction to the Study of Colour Vision. By J. H. Parsons, D.Sc, 

 F.R.C.S. [Pp. viii + 308, with 75 illustrations.] (Cambridge : at the 

 University Press, 191 5. Price \2s. bd. net.) 



This book is a well-written compilation of attractive appearance. Its chief defect 

 is that the author appears to possess so very little personal knowledge, as opposed 

 to book knowledge, of the facts bearing on disputed points. This is particularly 

 applicable when the author deals with my work. Though he has given my views 

 correctly his comments are so wide of the mark and show such an entire lack of 

 appreciation of the essential details that they are very misleading. The author 

 could not have written as he had if he had spent a single hour in my laboratory. 

 This even applies to his criticisms when he has adopted my conclusions in direct 

 opposition to his previous statements, as, for instance, in the use of colour names. 

 In a book published in 1912 he states, with reference to practical tests, "The 

 fundamental axiom in colour testing is that no importance should be attached to 

 the naming of colours." He now writes : " In practical testing the object aimed at 

 is the determination of whether the examinee recognises red, green, and white 

 lights as red, green, and white lights respectively, and it is obvious that the names 

 which he applies are of great importance." No explanation is given of this 

 change of front. Though as far as I am aware the author has never even looked 

 through my spectrometer, he cavils at the observations made with this instrument 

 and the classification of colour blindness made with it. This classification is 

 independent of any theory of colour vision, and the facts ought to have been 

 given a prominent place in the book. If a large number of persons be examined 

 with the spectrometer a certain proportion will be found to see two colours only in 

 the spectrum with an intervening colourless region which varies in size with 

 different persons. The fact that so many degrees of dichromic vision exist is one 

 of the milestones of the subject and requires explanation on any theory. It would 

 be just as sensible to object to a classification of potatoes as such because they are 

 not all of one size. The trichromic when examined with the spectrometer say 

 they see three definite colours in the spectrum— red, green, and violet, the yellow 

 and orange regions being designated as red-green and blue as green-violet. The 

 spectrum is also divided into about ten monochromatic regions instead of eighteen. 

 The monochromatic region is a fundamental physiological fact. The author 

 would do well and would make the book of much greater value if he would for 

 another edition ascertain for himself the truth or otherwise of the contradictory 

 statements of different authors so that he can give the facts in accordance with his 

 own knowledge. As far as I am concerned I shall be very pleased to give him 

 every help in my power. It is hardly fair to object to any fact when it has not 

 been examined by the critic. The intense reluctance which compilers have to 

 ascertain for themselves the truth of the simplest statements is responsible for the 

 continued propagation of error and the great difficulty which exists in the general 

 recognition of the simplest new facts when these are opposed to previous 

 statements. 



There are some grave omissions : the facts of colour adaptation are not even 

 mentioned. The book contains too much theory, and in some cases the theory 

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