532 



NATURE 



[October 13, 1923 



of monographs is not only inevitable but desirable. 

 The remaining chapters irive interesting accounts of 

 the pyronines and rnsamiiu^ , the constitution of 

 fluorescein and analogous compounds ; the con- 

 stitution of the rhodamines and their manufacture; 

 and the chemistry of the rhodols and anisolines. Of 

 special interest, from the general point of view, is the 

 discussion of the constitution of phenolphthalcin and 

 fluorescein, which is given in a manner which will 

 appeal to those students who have to approach these 

 difficult problems for the first time. 



The book is well printed and the very complex 

 formulae are particularly clear and easy to follow. It 

 is stated to have been printed in Saxony, and this 

 probably accounts for some of the quaint spelling 

 which has escaped the vigilance of the proof-reader. 

 " Recomends " on p. ii, " wather-bath " on p. 29, 

 the inverted commas on p. 66, " occour " on p. 289, 

 " preapare " on p. 269, " doubtfoul " on p. 38, " ac " 

 on p. 56, " annother " on p. 58, " occurence " on p. 64, 

 " alo " on p. 91, and " accridine " on p. 120 meet the 

 eye and are perhaps inevitable in the circumstances. 

 Moreover, it is difficult to know what the " dashes " 

 after the names of Williams and Hofmann on p. 55 

 really mean. But these are minor faults, and both 

 the author and the editor are to be congratulated on 

 the production of a volume which will long remain 

 the standard treatise on the subject with which it 

 deals. J. F. Thorpe. 



The Eye and Vision. 



The Present Status of Visual Science. By Dr. Leonard 



Thompson Troland. Pp. 120. (Bulletin of the 



National Research Council. Vol. 5, Part 2, No. 27.) 



(Washington : National Academy of Sciences, 



1922.) 1.50 dollars. 



THE eye can be regarded as holding a unique 

 position among the organs of special sensation, 

 because of all methods of observation, those carried out 

 by vision, either unaided or through the medium of 

 suitable accessory apparatus (e.g. the photographic 

 plate), are the most accurate, rapid, and susceptible of 

 the widest application. Moreover, the problems which 

 the eye presents for solution are of interest, not only to 

 the physiologist and anatomist, but also to the oculist, 

 physicist, psychologist, and the illuminating engineer, 

 and much has therefore been written by them in their 

 own respective spheres. So plentiful, in fact, has the 

 literature of vision become, that a complete master}' of 

 the subject is possible to few. Dr. Troland has there- 

 fore achieved a result of great value in the publication 

 of, the book before us. 



Early in the book, and again in the concluding pages, 



NO. 2815, VOL. 112] 



Dr. Troland utters a word of warning ; there are. !;• 

 points out, UK) many papers published on vision. Mai, , 

 authors, he says, " show a lack of acquaintance with t ! - 

 problems and results with which the others > 

 cemed " (p. 10), and " appear also to have a p. 

 contempt for existing literature, even when it is in tli< r 

 own language " (p. 1 10). In many papers there is " . n 

 absence of that complete siKcification of all circui; 

 stances surrounding experimentation which is neeci. i 

 to render the results of any permanent value " (p. 11, 



The reader of Dr. Troland's lx)ok will find that ti.< 

 pages which follow the introduction are written with 

 three objects in view : to indicate as clearly as possible 

 the lines of cleavage between the physiological, psycho- 

 logical, and physical aspects of vision ; to summarise 

 the well-established facts concerning the various 

 mechanisms associated together in the eye; and to 

 indicate the points where our knowledge is defective 

 or altogether absent. Owing to the necessity for 

 brevity it is not possible to go over all three parts of 

 Dr. Troland's book in this review. The last one will 

 alone be selected for detailed consideration, because 

 it recalls some of the well-established facts of vision 

 at the same time that it indicates the direction which 

 future research should take. 



Considering, in the first place, those eye structures 

 which co-operate to form an image on a retina. Dr. 

 Troland writes (p. 39) : " The ophthalmoscope, the 

 skiascope, and the corneal microscope (supplemented 

 by Gullstrand's slit-lamp) provide us with instruments 

 for examining the tissues of the living eye in a verj' 

 satisfactory way." Elsewhere he adds (p. 40) : " Helm- 

 holtz was able to work out satisfactorily the main 

 dioptric or refractive function of the eye from data of 

 optical anatomy, in combination with the established 

 general principles of physical optics." The word 

 " satisfactorily " in the above sentence unfortunately 

 cannot pass unchallenged, because, although we know 

 the positions of the principal points of the eye according 

 to Gauss's theorem with considerable accuracy, and 

 although we know that the eye suffers from certain 

 aberrations, the data from which we can calculate the 

 distribution of light intensity in the image formed on 

 the retina are ver\- deficient. Neither can we check 

 our calculations by direct obser\ations of the retinal 

 image, because the structures found in the retina are 

 insufficiently fine for the purpose, and we are unable 

 to remove the retina and examine the image by other 

 means without reducing the intra-ocular pressure, and 

 thus allowing the distances between the optical surfaces 

 to alter. 



What is wanted is a method of quantitative estima- 

 tion, applicable to the retinal image, no less accurate 

 than that devised by Hartmann for studying the 



