September 15, 1916] 



SCIENCE 



391 



out of cultivation. Mr. Middleton states that 

 the chief immediate cause of the increased 

 productivity of German soil is the increase in 

 use of artificial manures ; twice as much nitro- 

 gen, one third more phosphate, and five times 

 as much potash are used in Germany as on an 

 equal area of our cultivated land. The reason 

 Mr. Middleton gives for this failure of the 

 British farmer is want of education, but he 

 thinks that this defect in our educational sys- 

 tem is being remedied. There are, however, 

 undoubtedly other causes, which might more 

 quickly be removed, for the depression which 

 has affected British agriculture during the last 

 seventy and especially the last thirty or forty 

 years. — British Medical Journal. 



SCIENTIFIC BOOKS 



An Introduction to the Study of Color Vision. 

 By J. Herbert Parsons, D.Sc, F.R.C.S., 

 Ophthalmic Surgeon, University College 

 Hospital; Surgeon, Royal London Ophthal- 

 mic Hospital. Cambridge, University Press. 

 1915. 308 pp. 



Dr. Parsons has undertaken to present the 

 facts and the theories of color vision in such 

 form as shall be intelligible to the general 

 reader. He states in his preface: 



The vast literature on color vision consists al- 

 most entirely of papers written in support of 

 some particular theory. It is peculiarly difficult 

 to obtain a general and unbiased view of the sub- 

 ject. I have here endeavored to separate the best 

 established facts of color vision from the theories, 

 and have then discussed the chief theories in the 

 light of these facts. 



Accordingly he has divided his book into 

 three parts. The first part (pp. 1-157) is de- 

 voted to a statement of the facts of normal 

 color vision; the second part (pp. 158-192) 

 deals with the facts of color-blindness ; and the 

 remaining portion (pp. 193-299) discusses 

 theories of color vision. 



The author's statement of the facts of nor- 

 mal color vision is prefaced by a brief sum- 

 mary of such phenomena of physical optics 

 and such a description of the structure and 

 function of the visual organ as shall serve as 

 a basis for his subsequent discussion. This 



is followed by a description of the color 

 vision of the light-adapted eye and of the 

 dark-adapted eye, together with a summary of 

 the temporal and spatial effects of retinal 

 stimulation (after-images, contrast, color- 

 zones and the like). His chapter on the evo- 

 lution of the color-sense presents evidence de- 

 rived from the color vision of the lower ani- 

 mals, from the color vision of primitive peo- 

 ples, and from the color vision of infants. The 

 description of color-blindness summarizes the 

 findings obtained in various investigations of 

 certain typical deviations from normal color 

 vision. The chapters on theories of color 

 vision are prefaced by an historical sketch of 

 the development of color theories, and this is 

 followed by a summary statement of the most 

 widely accepted theories. 



Dr. Parsons has attempted a difficult task 

 in his endeavor to present a readable summary 

 of the exceedingly voluminous and exceed- 

 ingly controversial literature of color vision; 

 and his book bears evidence of painstaking 

 effort and keen insight. The author has exer- 

 cised sound judgment in selecting and pre- 

 senting his material; and for the most part he 

 has maintained an admirably non-partisan 

 attitude throughout — except, perhaps, in deal- 

 ing with the duplicity theory where his approval 

 is more complete than the facts seem to the re- 

 viewer to warrant. The features in Dr. Par- 

 sons's book which are most likely to excite criti- 

 cism are the author's tendency toward an un- 

 critical statement of the findings of the vari- 

 ous investigators, and his failure to recapitu- 

 late his mass of summaries and to give the 

 reader a brief statement of the present status 

 of the various problems. There is perhaps no 

 field of investigation in which the refinement 

 of apparatus and of technique has made 

 greater progress within the past decade or two 

 than in the field of color vision; it follows, 

 therefore, that many of the earlier investiga- 

 tions now possess no more than historical 

 value. It seems to the reviewer to be doubtful 

 wisdom to lump together the findings of good, 

 bad and indifferent investigations, and to pre- 

 sent them to the reader without any attempt at 

 critical evaluation. In several instances the 



