594 



NA TURE 



[Feurl'aky 3, 1 9 10 



are totally different from those of adult worms. It is 

 only exceptionally that such larvs can be reared, in 

 aquaria, to adults, and their identity definitely estab- 

 lished. In many cases the larvse do not present clear 

 specific or even generic characters, and they can there- 

 fore be referred only to their respective families. The 

 author has written a careful and detailed account, in 

 most' cases drawn from living specimens, of the prin- 

 cipal larval forms captured, some of which have not 

 been previously described. Measurements are given 

 of the length and diameter of the larvae, of some of 

 the parapodia and setse, and of the cilia; and the 

 colour markings are recorded. The larvae dealt with 

 are as follows :— three Syllids, several Polynoids, three 

 Phyllodocids (including Mystides and probably 

 Eulalia), Nephthys, Spio, and four other Spionids, one 

 of which is possibly the larva of the elusive Poecilo- 

 chcEtus, Polydora, and two other Polydorids, Mage- 

 lona, Chatoptcrus, and Pectinaria, the metamorphosis, 

 to the young adults, of the metatrochophoral larva of 

 the last-named being described. The account of these 

 larva, which is illustrated by means of forty-seven 

 figures, will be welcome to many \vorkers on plankton 

 and^ on polychats, and, although it is admittedly a 

 preliminary account, it forms a good basis on which 

 to found future observations. The reader is referred 

 for a definition of the numerous technical terms em- 

 ployed in describing the different stages and larval 

 organs to a recently published paper by the same 

 author, but it would have been a considerable advan- 

 tage and convenience to the reader if brief definitions 

 of these terms had been given at the beginning of the 

 present memoir. 



We suggest to the editor of these memoirs that all 

 the volumes published in the future be provided with 

 a table of contents. 



ENGINEERING SCIENCE. 

 (i) Applied Mechanics, Embracing Strength and Elas- 

 ticity of Materials, Theory and Design of Structures, 

 Theory of Machines and Hydraulics. A Text-book 

 for Engineering Students. By Prof. David Allan 

 Low. Pp. vii + 551. (London: Longmans, Green 

 and Co., 1909.) Price 7s. 6d. net. 



(2) Strength of Material: an Elementary Study pre- 

 pared for the Use of Midshipmen at the U.S. Naval 

 .icademy. By H. E. Smith. Second edition. Pp. 

 ix + 170. (New York: John Wiley and Sons; 

 London: Chapman and Hall, Ltd., 1909.) Price 

 5^. 6d. net. 



(3) Stresses in Masonry. By H. Chatley. Pp. 

 viii + 142. (London: C. Griffin and Co., Ltd., 

 1909.) Price 3i-. 6d. net. 



(i) 'T^HE subject covered by this book is a very 

 -•- extensive one, and the author is to be con- 

 gratulated on the fact that by judicious compression, 

 without sacrifice of clearness, he has in a volume of 

 °"'y 55° pages covered ground to which usually two 

 or three bulky text-books are devoted. No student 

 can expect, however, to make himself master of the 

 contents of the book unless, as the author himself 

 suggests in his preface, he works conscientiously 

 NO. 2IOI, VOL. 82] 



through the sets of carefully thought-out problems 

 which are given at the end of each chapter. At the 

 end of the first, or introductory, chapter, Prof. Low 

 has given a fairly complete bibliography for the sub- 

 ject, confining himself to works in the English 

 language which have appeared during the last decade, 

 or to those works which have been brought up to 

 date by new and revised editions ; this list will be 

 found of considerable use by students who desire to 

 extend their reading in any one branch of the subject. 

 The first five chapters are devoted to a series ol 

 introductory problems, work and energy, polygon of 

 forces, moments and centroids, and for these latter 

 both graphical and analytical methods are discussed ; 

 then follow six chapters on strength of materials. In 

 the chapter dealing with compound strains and 

 stresses, the opinion is expressed that in the case of 

 ductile materials, such, for example, as mild steel, it 

 is the resistance to shear which determines the 

 strength, and reference is given to the experimental 

 work of Guest, Hancock, Scoble, and others in in- 

 vestigating this problem. The whole of this chapter 

 is well worth the careful study of the young engineer, 

 who should not be content to leave it until he feels 

 that he has made himself a thorough master of the 

 principles laid down, and of the formulae deduced for 

 practical use in design work. Another chapter in 

 this section which contains a well-arranged mass of 

 information is that on the behaviour of materials in 

 the testing machine ; the latest memoirs have been 

 summarised, and the conclusions to be drawn from 

 these experimental investigations are clearly set forth. 



In chapters xii. to xv. stress diagrams and the 

 design of roofs and bridges are discussed, and, though 

 of necessity there is much condensation, all the im- 

 portant points are clearly brought out. A student 

 who has mastered this section will find that his work 

 is much simplified when he comes to the study of one 

 of the more advanced text-books specially devoted to 

 this branch of engineering work. 



The next eleven chapters are devoted to the subject 

 of mechanism; such details as friction and lubrication, 

 governors, toothed gearing, balancing of revolving 

 and reciprocating masses, &c., are discussed in a 

 satisfactory manner, and velocity and acceleration 

 diagrams and crank effort diagrams receive due 

 attention, though there is nothing novel in the method 

 of treatment. 



The last section of the book treats of hydraulics ; 

 the flow of water over weirs and through orifices and 

 pipes, loss of head due to various causes, and the 

 impact of jets on vanes are all in turn discussed, and 

 the application of these principles to the design of 

 such hydraulic machinery as water-wheels, turbines, 

 pumps, and accumulators is then explained. 



Prof. Low has succeeded in writing on a well-worn 

 subject a text-book with many new features, and one 

 which should find a place on the bookshelf of every 

 )'Oung engineer. 



(2) This small text-book was prepared for the use 

 of the midshipmen at the U.S.A. Naval Academy in 

 connection with one of the courses in the department 

 of mathematics and mechanics. It deals, therefore, 



