214 



NA TURE 



[December 24, 1908 



graphical expression and reduction of results, and a 

 number of algebraical summations for the later ap- 

 plication of calculus from first principles. 



The measurement of distance, mass, and time calls 

 for little remark. The apparatus described is not 

 novel, but is fairly complete, comprising as it does 

 all the common instruments of precision and the pre- 

 cautions necessary for correct use. Here particularly 

 the absence of theoretical considerations is noticed, the 

 derivations of the units not receiving notice, e.g. no 

 definition of the second is given. 



The tliird chapter deals with measurements of small 

 quantities by means of the optical lever, a rather un- 

 common experiment on a spirit-level, and a very good 

 treatment by simple algebra of Amsler's planimeter. 



Then follows a very limited introduction to velocity 

 and acceleration, the only acceleration determined 

 being g by the usual pendulum observations. Specific 

 gravities and the calibration of weights are treated 

 exhaustively. 



The chapters on moment of inertia and elasticity are 

 somewhat difficult, as the explanations are complex 

 algebraically. The experiment on moment of inertia 

 by torsional oscillations is sound, but the experiment 

 for Young's modulus is open to serious error due to 

 slipping in the grips at both ends. The definition of 

 " brittleness " is misleading; those of flexure and 

 rigidity are diflicult but correct. 



The chapter on viscosity includes a good description 

 of Poiseulle's capillary-tube experiment. 



The measurement of temperature is, on the whole, 

 accurately and completely given. The statement that 

 gas thermometers can be used up to 1700° C. is not, 

 however, correct so far as accuracy is concerned. 

 Again, for the resistance thermometers difficulty of 

 experiment has led the authors to evade the sulphur 

 point and to minimise its importance. Mercury-in- 

 glass thermometers are fully treated. 



The experiments on the expansion of rods are open 

 to the objection that the temperature must be indeter- 

 minate near the ends. The absolute expansion of 

 mercury and the cubical expansion of glass are given 

 more successfully. 



The difficult subject of calorimetry receives consider- 

 able attention and is sound. The method of mix- 

 tures, the bomb calorimeter, and the Junker calori- 

 meter are described fully as pieces of apparatus most 

 suitable for their respective purposes. 



An extremely short chapter gives an introduction to 

 the principle of the conservation of energy, and the 

 book concludes with some useful tables of physical 

 constants. L. B. 



THE EDIBLE CRAB. 

 L.M.B.C. Memoirs. XVI. Cancer. By J. Pearson. 

 Pp. xviii + 209. (London : Williams and Norgate, 

 1908.) Price 6s. 6d. 

 T T is a remarkable thing, perhaps, that although the 

 -•- edible crab is of so much importance as an article 

 of food, and is also an easily obtained subject for the 

 study of the morphology of the brachyurous Crustacea, 

 NO. 2043, VOL. 79] 



this is the first concise statement of its structure and 

 habits that has been published in any language. 



It might have been advisable if the editor of the 

 series had departed from his usual practice and allowed 

 in this case the use of a short subtitle to the memoir, 

 such as " the edible crab," since the books that have 

 been published upon " Cancer " in recent years are 

 without number, whereas this is the only one on the 

 crab. 



The need of a memoir on the subject has long been 

 felt, as the records of investigation are scattered and 

 somewhat diflicult of access ; but Mr. Pearson has 

 evidently devoted very great care and patience to the 

 collection of all the available information, and, having 

 added to it a great deal that is new, he has produced 

 a work which will certainly prove to be one of very 

 great utility. 



The author has a liberal conception of what is neces- 

 sary in a memoir concerning a single species, and he 

 gives not only a detailed description of the external 

 features and general anatomy, but also some important 

 and useful notes on the histology and physiology. 

 There are two surprising facts about Cancer which 

 may be learned from this memoir. The one is that 

 we know very little about the larval development of 

 an animal that is so common and so useful, and 

 absolutely nothing about its pre-larval stages. It may 

 be that the early development follows a course 

 that we might expect from our knowledge of these 

 stages in other crabs; it may be that the study of 

 these stages would not produce any facts of practical 

 importance ; but it is an object-lesson on unexplored 

 fields of marine biological investigation that we have 

 to confess to such ignorance about a familiar type. 

 The second surprising fact, but not a new one to those 

 who study fishery statistics, is that the value of the 

 annual catch of crabs on the coasts of England and 

 Wales alone is nearly 6o,oooZ. But notwithstanding 

 this fact we are indebted to the energy of Prof. Herd- 

 man and his colleagues for the greater part of the 

 necessary funds for the production of a memoir which 

 must prove to be of great economic value. 



For the advanced student of zoology the memoir will 

 undoubtedly prove of the greatest assistance when he 

 comes to the dissection of the crab, and he will learn 

 to appreciate the concise and, so far as we have been 

 able to test them, accurate statements of anatomical 

 facts and the thirteen beautiful plates by which the 

 memoir is illustrated. It would have been better if 

 the descriptions of the figures had been in many cases 

 extended, so that the reader could see at a glance the 

 principal points that each figure is intended to illus- 

 trate. When there are so many plates, and no less 

 than six full pages of reference letters arranged in 

 alphabetical order, the system adopted becomes rather 

 tiresome to the reader. It would also have been useful 

 to the student if Mr. Pearson had given a short state- 

 ment concerning the other common crabs of the coast 

 for which Cancer might be mistaken and the prin- 

 cipal features which distinguish them. But the 

 memoir may be heartily welcomed as it is, and Prof. 

 Herdman and Mr. Pearson congratulated on its 

 publication. 



