246 



NA TURE 



[December 30, 1909 



As a reference to ancient observations it should also 

 prove valuable. 



The dynamical period will appeal more to the 

 student, its main theme being, of course, the estab- 

 lishment of the principles of universal gravitation by 

 the work of Kepler, Newton, Laplace, Halley, and the 

 others. The section on observation gives an abbre- 

 \iated account of the methods and instruments em- 

 ployed in the more important and epoch-making re- 

 searches, and contains a deal of interesting matter. 



The fourth book, dealing with the physical period, 

 is, pel haps, the least satisfying, but the chief reason 

 for this, probably, is the confined space in which a 

 tremendous amount of matter has to be discussed. 

 .As the author states on p. 147, he has been "compelled 

 so often by the limits of space to stimulate without 

 satisfying inquiry," and on these lines the book must 

 be welcomed as a success. Those stimulated will find 

 a useful, brief bibliography, to assist them in their 

 further inquiries, given at the end of the volume. 



W. E. R. 



Wild Floivers and Trees of Colorado. Bv Dr. F. 



Ramaley. Pp. viii+178. (Boulder, Colorado: 



A. A. Greenman, 1909.) 

 This book consists of two chapters, in the first of 

 which the author presents a general .sketch of the 

 vegetation, and in the second he deals with the forests. 

 Vegetation in the State of Colorado is exceedingly 

 diverse by reason of the varied conditions of climate, 

 and owing to the great variation in altitude the vertical 

 distribution is more pronounced than the horizontal 

 distribution, so that the author groups his associations 

 according to the zones of elevation. There is little 

 information regarding specific wild flowers beyond the 

 illustrations of a dozen selected types and no system- 

 atic enumeration is supplied. Tlie book is copiously 

 illustrated with photographs of characteristic scenes or 

 formations and the flowers referred to, making the 

 text shorter than might be anticipated. The survey of 

 the forest formations is more concrete, and twenty of 

 the principal tree or shrubby genera are detailed 

 with respect to the species and their diagnostic char- 

 acters. The author announces the book as an in- 

 troduction to Colorado botany, so that he may perhaps 

 be subsequently induced to compile a flora of this 

 interesting region. 



(i) The Hisforic Thames. By Hilaire Belloc. Pp.204. 



(London : J. M. Dent and Co., 1909.) Price 3s. bd. 



net. 

 {2) The Heart of England. By E. Thomas. Pp. xi-i- 



244. (London : J. M. Dent and Co., 1909.) Price 



3.?. 6d. net. 

 (i) The first of these prettily-bound volumes is a new, 

 cheaper edition of Mr. Belloc's essay on the Thames, 

 which was issued originally in a limited edition, cost- 

 ing a guinea net. The Thames and its valley is dealt 

 with from every point of view, and the interesting 

 description reveals an intimate knowledge of the sub- 

 ject. The reader's task would have been easier had 

 the book been divided into chapters; the index, not- 

 withstanding its completeness, scarcely takes the place 

 of a judicious division of the essay into sections accord- 

 ing to subjects. 



(2) The second volume is a similar re-issue of essays 

 on subjects the most diverse. Ranging as they do 

 from "Walking with Good Company" to "The Har- 

 vest Moon " or " Fishing Boats," they will make an 

 appeal to readers who can enjoy something other than 

 wild adventure or thrilling incident. Mr. Thomas 

 does not treat his subjects too seriously, and to read 

 his essays will give much the same pleasure as listen- 

 mg to bright, pleasant conversation in which quiet 

 humour takes its proper place. 

 NO. 2096, VOL. 82] 



LETTERS TO THE EDITOR. 



[The Editor docs not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part 0/ Nature. 

 No notice is taken of anonymous communications.] 



Are the Senses ever Vicarious ? 



The interesting correspondence in X.mure of December 2 

 from Mr. G. 1. Walker and Prof. McKendrick has re- 

 minded me of a passage in Nietzsche which will be found 

 at the end of paragraph 192 of " Beyond Good and Evil." 

 The passage has been translated as follows : — 



" In an animated conversation I often see the face of 

 the person with whom I am speaking so clearly and sharply 

 defined before me, according to the thought he expresses, 

 or which I believe to be evoked in his mind, that the 

 degree of distinctness far exceeds the strength of my visual 

 faculty — the delicacy of the play of the muscles and of the 

 expression of the eyes must therefore be imagined by me. 

 Probably the person put on quite a different expression or 

 none at all." 



Nietzsche's experience appears to suggest that a pre- 

 sentation, which is in form purely visual, may show 

 evidence of a synthesis out of elements which are not 

 solely of visual origin. No doubt, as Nietzsche says, the 

 imagination plays an important part, and the same may 

 be said of the memory; but Mr. Walker's experience 

 seems to prove that in his case some of the elements out 

 of which sucli a visual presentation are synthesised mav 

 be definitely of auditory origin. Perhaps to a psychologist 

 this may not appear very surprising: but it certainly does 

 seem a little surprising that, when the main source of Mr. 

 Walker's visual experiences was cut off by the loss of his 

 sight, the surviving auditory elements should alone be 

 strong enough to continue to evoke presentations in visual 

 form. 



That the above is the explanation of Mr. Walker's 

 experiences there seems little doubt. The play of ex- 

 pression which he " sees " will naturally follow the varia- 

 tions in the tone, &c., of the speaker's voice; but it is 

 scarcely so certain that it will reproduce the actual ex- 

 pression of the speaker. As to the circumstance that Mr. 

 Walker only " sees " the upper part of the speaker's face, 

 as a rule, one may hazard the guess that this arises from 

 the fact that in conversation the attention is generally 

 concentrated on that part, with the result that the elements 

 corresponding to it in the visual presentation are the most 

 intense, and hence most likely to survive the destruction 

 of their principal source. Presumably that which Mr. 

 Walker sees is devoid of colour ; but it would be interest- 

 ing to know how the present intensity of his visual pre- 

 spntations compares with their intensity when he originally 

 lost his sight. 



Mr. Walker's preference for a position at an angle to 

 the speaker possibly depends on the fact that he thereby 

 secures a more marked difference between the sensations 

 proceeding from the two ears — a difference analogous to 

 the difference between the sensations received from the two 

 eyes. Hugh Birrell. 



Holyrood House, Bo'ness, Linlithgowshire, N.B., 

 December S. 



The very interesting observations recorded in Mr. 

 Walker's letter in N.iture of December 2 confirm in a 

 remarkable manner the view I have always held, that in 

 a very literal sense "seeing is believing"; that is, that 

 a visual im.age is not an image on the retina, but a mental 

 representation of what the percipient believes to be before 

 him. As a rule, no doubt this mental representation is 

 suggested by sense impressions coming via one or both 

 optic nerves, but this is not necessarily the case : and it 

 ought to cause Prof. McKendrick no surprise whatever 

 to find Mr. Walker, though blind, perceiving visual 

 images, which in his case are apparently suggested mainly 

 by sense impressions coming through the auditory nerve. 



There are, of course, plenty of arguments drawn from 

 everyday life which point to the same conclusion, but 

 which are so commonplace that we take them for granted 

 without attempting to analyse their significance. I will 



