796 



SCIENCE. 



[N. S. Vol. VIII. No. 205. 



truth on thousands of students in their intro- 

 ductory courses of physics and physiology. 

 When von Helmholtz elaborated the hypothesis 

 jt was of great value in coordinating the then 

 known phenomena and in giving a basis for fur- 

 ther research. But forty years have brought 

 many changes, and if the hypothesis were now 

 proposed anew by an unknown man it would 

 not find a single adherent. No modern student 

 of organic evolution can conceive how the three- 

 fiber mechanism could develop from a unicellu- 

 lar organism already sensitive to light. No 

 psychologist can conceive how three kinds of 

 fibers make us see three primary colors as_^white 

 light ; they would more probably lead us to see 

 white light as three colors, I should suppose. 

 All the newer phenomena — the spectrum of 

 faint light, color-blindness, contrast, after- 

 images, the variations in the field of vision, 

 etc. — not only do not support the hypothesis, 

 but must be subjugated to it by unlikely sub- 

 sidiary hypotheses. The phenomena of space 

 perception are too complex to enter into here, 

 but the ' empiristic ' theory, of which von Helm- 

 holtz was properly proud in the sixties, seems 

 now, after the writings of James, Ward, 

 Stumpf and others, particularly naive. 



With some reluctance I must state that not 

 only are the theories of the Physiologische Optik 

 in large measure outgrown, but that in many 

 cases the observations cannot be verified. In 

 subjects in which I have myself worked — after- 

 images, the discrimination of intensity, conflict 

 of the fields of vision and others — new methods 

 have given different and probably more correct 

 results. This is the natural course of science. 

 The work of a great investigator, if vital, must 

 be the ladder by which we climb, but which we 

 afterwards discard. The Physiologische Optik 

 is still a great storehouse of facts and observa- 

 tions of contemporary importance, but we should 

 regard it as closed thirty years ago. 



The bibliography compiled by Professor 

 Konig is an extremely useful piece of work, but 

 I see no adequate reason for appending it to the 

 Physiologische Optik. It may be delusive in 

 leading the thoughtless to suppose that von 

 Helmholtz had considered all these works ; it 

 makes the book needlessly bulky and expen- 

 sive ; it is compiled chiefly at second hand, with 



many omissions and numberless minor errors.* 

 Such an index should be published separately, 

 and, if possible, revised and brought up to date 

 every few years. 



The criticisms that I have ventured to make 

 apply only to the revision of the Physiologische 

 Optik. If the first edition had been reprinted 

 without alteration there would be nothing to 

 express but admiration for a work of genius al- 

 most unrivalled in the history of science, and 

 for a man of genius whose intellect was so pro- 

 found and so far-reaching that of his contempo- 

 raries only Darwin stands beside him. 



J. McKeen Cattell. 



Columbia University. 



Elementary Botany. By Geo. F. Atkinson. 



New York, Henry Holt & Co. 1898. 12mo. 



Pp. xxiii-f 444. 



This latest and best of elementary text-books 

 of botany is a thoroughly commendable work, 

 and reflects high credit upon the author and 

 upon the publishers. In pleasing contrast to 

 the larger number of books with similar titles 

 and kindred scope it is fresh, accurate, compre- 

 hensive and readable. It must have a heavy 

 sale as soon as teachers of botany become ac- 

 quainted with its merits, for in no other Ameri- 

 can elementary botany now before the public 

 is the subject-matter so thoroughly covered and 

 the illustration so illuminating and suggestive. 



The text has been classified by its author 

 under three captions, physiology, morphology 

 and ecology, in the order given, a modification 

 of the ordinary arrangement. In the first 



* Thus, in regard to American writers eighteen 

 references are given to Professor Le Conte, but his 

 book on ' Sight ' is not included. A comparatively 

 unimportant article by an American author is quoted 

 three times, probably by accident. We find ' Bow- 

 ditsch ' four lines after the name has been correctly 

 given. My own name is given twice "within five 

 lines spelled incorrectly in two different ways. Mrs. 

 Franklin's name occurs four times, each time differ- 

 ently. Professor Le Conte Stevens' name occurs five 

 times in four different ways, never quite correctly. 

 One of Professor Stevens' articles is said to be in the 

 'Amer. Journ. of So. Vol. XXIII.,' and the contin- 

 uation of the article in the next number of the same 

 journal is said to he in ' Sill. Journ. XXIII.' Indeed, 

 I have noted sixteen different ways in which The 

 American Journal of Science is referred to. 



