74 



NA TURE 



[November 23, 1893 



the book, usefully take the place of a multitude of im- 

 posing but superfluous symbols. 



Another notable point in the investigation, to vvhi'h 

 attention should be drawn, is the mode of obtaining the 

 expression for the probability of collision. This is given 

 as proportional to the component of the relative speed 

 along the line of centres at impact ; and not to the 

 relative speed itself, though this is proved to be the case 

 Hi v5 5. The final result, however, is rendered correct bv 

 means of a compensating error in the specification of 

 the element of space really involved. This procedure 

 cannot fail to bewilder a thoughtful reader. 



All these remarks, it is to be observed, are made on 

 the very first proposition in the work : — the "green tree," 

 as it were ! What m'ght not be expected in the " dry" ; 

 i.e. the demonstration of BoUzmann'a Theorem, to which 

 the book gradually leads up ? But I must not now re- 

 capitulate the objections which I made (about 1886-S) to 

 Boltzmann's methods, nor the modes in which he defended 

 them. Those who are curious about the matter may be 

 referred to the Phil. Mat^. for that period. All I need 

 here say is that I do not think that Dr. Watson's book 

 meets any of my objections. 



From the experimental point of view, the first great 

 objection to Boltzmann's Theorem is furnished by the 

 measured specific heats of gases ; and Dr. Watson's con- 

 cluding paragraphs are devoted to an attempt to explain 

 away the formidable apparent inconsistency between 

 theory and experiment. In particular he refers to a little 

 calculation, which I made in 1886 to show the grounds 

 for our confidence in the elementary principles of the 

 theory. This was subsequently verified by Natanson 

 (IVied. Ann 1S88) and Burbury {P/ii/. Trans. 1S92). Its 

 main feature is its pointing out the absolutely astounding 

 rapidity with which the average amounts of energy per 

 particle in each of two ssts of spheres in a uniform 

 mixture approach to equality in consequence of mutual 

 impacts. Thus it placed in a very clear light the difficulty 

 of accepting Boltzmann's Theorem, if the degrees of 

 freedom of a complex molecule at all resemble those of 

 an ordinary dynamical system. P. G. Tait. 



A HISTORY OF CRUSTACEA. 

 A History of Crustacea. Recent Malacostraca. By the 

 Rev. Thotnas R. R. Stebbing, M.A. With numerous 

 illustrations. (The International Scientific Series, 

 Vol.lxxiv.). (London: Kegaa Paul, Trench, Tri.ibner, 

 and Co., Ltd., 1893.) 

 " nPHE ambition of this voluine," writes the author in 

 J- his preface, " is that it shall be one to which 

 beginners in the subject will naturally have recourse, and 

 one which experienced observers may willingly keep at 

 hand for refreshment of the memory and ready reference." 

 A most laudable ambition, and one that the author, we 

 doubt not, set out with an intention to fulfil. The want 

 of a volume of this very sort upon this subject had been 

 often felt by both the student and the expert. The advance 

 in our knowledge of the group had made it impossible to 

 annotate effectively that model " History of the Crus- 

 tacea," written by Milne Edwards, and Mr. Stebbing's 

 painstaking, excellent memoir on the Amphipods of the 

 N"). 1256, VOL 49I 



C/talleui^er Expedition had pointed him out as a pos- 

 sible author of a useful manual. To write, however, a 

 useful manual or history requires that one should take a 

 wide and all-sided view of the subject, so as to secure a 

 fair symmetry in its treatment ; once the amount of detail 

 to be given has been determined upon it should be 

 rigidly adhered to, and, needless almost to add, no useless 

 or unnecessary matter should be allowed to obtrude, 

 itself. Therefore, to a knowledge of the subject there 

 must be added certain powers of judgment, to which it 

 would be well to join certain gifts of style, in order that 

 a satisfactory result might be obtained. 



None will deny to the author of this history of Crus- 

 tacea a knowledge of his subject, and the immense 

 amount of facts that he has condensed into the four 

 hundred small pages of this volume will astonish those 

 who peruse it. But for all this there is abundant 

 evidence that it was begun without any sort of judicious 

 calculation as to its scope, and Hie reader will be as sorry 

 on the discovery as we fancy its author was, that the diie 

 necessity of space has made what purports to be a history 

 of the Crustacea into only a manual of the Malacostraca, 

 and not even a complete manual of this sub- class, for at 

 page 436 we read: "To complete the sketch of the 

 Malacostraca, the sub-order of the Amphipoda reinaitts to 

 be described.^' Chapters describing this sub order had 

 been written, when it appeared they overflowed the utmost 

 space that could be allowed, and with this statement the 

 " History of the Crustacea" ends. Our sympathies are 

 with the author, for might we not have expected something 

 excellent about a sub-order that he had made so peculi- 

 arly his own, and had we not a right to expect, after 

 reading the first fifty pages, some information about the 

 vast swarms of Entomostraca and Cirripedia. Apparently 

 it was all ready, but the author was met with a " to so far 

 you may print, and not a page further." The promises 

 of what may be in the future seem too uncertain to 

 depend upon. 



Having thus expressed our disappointment about what 

 we have not been given, we proceed to record our 

 opinions as to what the publishers have allowed. The 

 volume opens with an introduction of some fifty pages, 

 which treats of the classification of the Crustacea in out- 

 line, giving us brief details of the sub-classes and orders, 

 notes on the geographical distribution, hints as to col- 

 lecting, statements about size and description of the 

 segments and their appendages. This is followed by a 

 table of the sub-classes, orders and sub-orders, and the 

 account of the Malacostraca, as far as the end of the 

 Isopoda. The plan adopted is to give a short diagnosis of 

 the orders and sub-orders, the tribes and families; under 

 these last, the principal genera and some of the more im- 

 portant species are given. 



While dates are appended to the genera, and the 

 names of the describers are given, yet there are only in 

 two or three instances any indications as to where the 

 descriptions are to be found. It would have added much 

 to the value of the work had it been possible to have 

 given these, but of course it would have added (what- 

 ever scheme was adopted) very greatly to the am umt of 

 the text. Possibly a little more information of this sort 

 might have been squeezed in had the pen been struck 

 through a number of useless sentences which rather 



