436 



NA TURE 



[September lo, 1903 



book. That even scientific men are too prone to take 

 a plausible hypothesis as proved, and to fill in the 

 little gaps in the observed facts with more or less 

 probable assumptions, is unfortunately true in many 

 branches of research besides the one in question, and 

 the work even of an advocatus Diaboli may be of value 

 if only to point out the places in the theory where these 

 assumptions occur. Particularly has this been the 

 case in the domain of nerve physiology, and the present 

 volume is a useful corrective. 



The earlier part of the book is occupied with a 

 historical review. Commencing with Waldeyer, His 

 and Forel, Dr. Nissl gives an account of the origin 

 and development of the neurone theory, with the 

 various additions, alterations, and subtractions made 

 by Hoche, Miinger, Verworn, and the other investi- 

 gators who have treated the subject. Allowing for 

 a little very pardonable controversial bias, the summary 

 is a just and able one, and Dr. Nissl's comments are 

 well conceived ; so that, although there are a few 

 points on which different opinions may be held — for 

 example, as to the weight to be attached to the work 

 of Forel — yet, as a whole, we may take the history of 

 the neurone theory here presented to us as the most 

 complete and trustworthy one yet published. 



The latter part of the book contains the author's 

 reasons for dissenting from the generally received 

 opinion of the structural unity of the elements known 

 as " neurones." He points out that the idea of con- 

 tact of nerve elements as opposed to that of continuity 

 is not necessarily dependent on the neurone theory, 

 and that the present methods of microscopic technique 

 are not sufficient to give a final answer in the matter. 

 The conclusion is therefore not so much that Dr. 

 Nissl's own views are necessarily correct as that the 

 rival opinions of the authors already mentioned have 

 not sufficient basis in observed facts, and should be 

 received with very much more reserve than has 

 commonly been the case. It is not, however, possible 

 to give a fair abstract of Dr. Nissl's contentions within 

 the compass of a review, and the book itself must be 

 consulted for further details. It will be found to well 

 repay careful reading, though the unwieldy size, the 

 absence of an alphabetical index — partly made up for 

 by very full chapter-headings — and the fact that, follow- 

 ing the German custom, the author has given no sum- 

 marised conclusion, render it difficult without consider- 

 able labour to disentangle the essential from the non- 

 essential portions of the treatise. 



OUR BOOK SHELF. 

 The Cloud World, its Features and Significance. By 



Samuel Barber. Pp. xii+139. (London: E. Stock, 



1903.) Price 7s. 6d. 

 In this volume Mr. Barber's object has not been to 

 write a scientific treatise on cloud formation, but rather 

 to put before us his own carefully made observations, 

 and " to commend to the tourist, the cyclist, and the 

 •city man a delightful and refreshing field of study 

 which may add a charm to a summer holiday." With 

 this object the book has been illustrated with a large 

 number of excellent photographs and sketches, and 

 contains many hints on the prognostic value of 

 different appearances of the sky. We cannot help 

 thinking that it would have gained in value if Mr. 



NO. 1767, VOL. 68] 



Barber had added, or, better still, prefaced, a short 

 chapter on the classification of clouds adopted by the 

 International Committee. This would have familiar- 

 ised his readers with the generally accepted termin- 

 ology of the subject ; the glossary partly answers this 

 purpose, but it enumerates so many different cloud 

 forms that it might become confusing to one entirely 

 unfamiliar with the subject. . 



When dealing with the physics of the atmosphere 

 Mr. Barber is distinctly less happy. Though the book 

 is not a scientific treatise, it ought not to contain state- 

 ments such as the following. 



In discussing the question of the suspension of 

 water particles in the atmosphere we read, " The 

 mechanical problem is exactly analogous to that of a 

 bird's flight. If the bird is shot it drops for want of 

 a propelling force : just so with the water vapour. It 

 is not sufficient to assume the vesicular form of water 

 in cloud molecules ; we should need to assume a higher 

 temperature in the air enclosed by the vesicles than in 

 the surrounding atmosphere. How can this be main- 

 tained, especially at great elevations? " The hypo- 

 thesis that clouds consist of hollow water vesicles 

 received its death blow about the middle of last 

 century when Stokes calculated the limiting velocity 

 of a falling drop ; since that date the suspension of 

 water globules in the atmosphere has ceased to be 

 a stumbling block to physicists. A few pages later 

 we find the statement, " Various forces affect water 

 and ice particles ; e.g. heat, electricity, gravity between 

 particles, gravity towards mountains and other 

 prominences, gravity to the earth, and last, but not 

 least, the force of crystallisation. . . . Let anyone 

 watch the formation of ice crystals on still water, and 

 he will have an idea of the extent of this force." Are 

 we to understand from this that " gravity towards 

 mountains " affords an explanation of the tendency 

 of clouds to form near the summit of a mountain? 



The reader who is inclined to make the study of the 

 appearance of the sky his hobby will find much to 

 interest him in the descriptive part of the book, but 

 he must be prepared to take many of the physical ex- 

 planations it contains cum grano satis. 



Graphical Statics Problems, with Diagrams. By 



W. M. Baker, M.A. Pp. 60. (London : Edward 



Arnold, n.d.) Price 2s. 6d. 

 This is a compilation of sixty problems in graphical 

 statics, many of them taken, by permission, from the 

 army entrance examination papers. Each problem is 

 accompanied by a diagram, and has a separate page 

 allotted to it. This leaves plenty of room for the 

 problem to be worked graphically on the page itself, 

 without requiring the diagram to be transferred to 

 drawing paper. The pages are perforated, and are 

 easily removed if desired. 



There is, perhaps, some unnecessary repetition and 

 not enough diversity in the problems. We would 

 suggest for a future edition that problems be included 

 involving a direct appeal to experiment in verification 

 of the principles of the polygon and the lever ; and the 

 scope of the subject might well be extended by the 

 introduction of position, displacement, velocity, and 

 momentum vectors, including vector differences, thus 

 helping very materially to an adequate understanding 

 of Newton's great law. Students should always 

 measure their graphical results, and an appendix con- 

 taining numerical answers would have been found 

 very useful in this connection. 



But the design of the book and the arrangement of 

 the problems greatly facilitates the work of the teacher, 

 and the volume can be strongly recommended to all 

 who wish to include this very important branch of 

 geometry in their curriculum. 



