NATURE 



[July 6, 191 x 



prove without further investigation (e.g. by Stokes's 

 method) that if the components are zero initially they 

 always will remain zero, for a similar argument 

 applied to uniformly accelerated motion from rest 

 would lead to a reductio ad absurdum. Does not the 

 author, however, assume this inference? Again, in deal- 

 ing with flow of a viscous liquid between two parallel 

 plates, would it not be more correct to say that Hele- 

 Shaw first made the experiments, and Stokes subse- 

 quently showed that the results were largely due to 

 viscosity, although it was previously thought, and 

 perhaps even incorrectly stated, that these motions 

 represented an actual realisation of two-dimensional 

 flow of perfect liquids? 



(2) Prof. Timerding's introduction to "Graphical 

 Statics " contains a praiseworthy attempt to bridge 

 over the gap which so often exists between treatises 

 of a purely theoretical character, and text-books deal- 

 ing too exclusively with technical applications. In 

 particular the author shows clearly the equivalence 

 which exists between the equations of equilibrium of 

 uniplanar analytical statics and the geometrical con- 

 structions of force diagrams, funicular polygons, and 

 stress diagrams of loaded frameworks, such as roof 

 trusses. It is not surprising to find the author com- 

 pelled to limit the scope of his book to the simplest 

 portions of the subject. By this means he rightly 

 claims to have produced a handbook which is access- 

 ible to students possessing a limited knowledge of 

 mathematics (including very elementarv analytical 

 geometry but excluding calculus), but which consti- 

 tutes a self-contained and connected exposition of the 

 subject-matter of which it treats. As the author points 

 out, the book should show to the technical worker 

 that he can derive help and elucidation even 

 from apparently abstract theories, while, on the 

 other side, the mathematician will see with pleasure 

 how densely the path of practice is strewn with the 

 finest flowers of theory. 



(3) "Vibrations of Systems having One Degree of 

 Freedom " is a tract of a rather more elementary 

 character than the series of "Cambridge Mathematical 

 Tracts " which have proved so useful already. It 

 might afford a useful supplement to existing text- 

 books for such students of physics as have attended 

 a suitable course of preparation in the elements of the 

 calculus and differential equations. The equations of 

 free and forced oscillation with one coordinate are 

 discussed, and are applied to such problems as the 

 rolling of ships and its measurement bv the pendulum. 

 The main difficulty is for students to find time to read 

 such tracts when they have so much other subject- 

 matter to study; this difficulty can probably be over- 

 come by placing the book in the hands of the lecturer 

 rather than of the pupil. There is certainly much to 

 be said for requiring students to get a clear under- 

 standing of vibrations with one degree of freedom 

 before introducing them to the more general problem 

 where there are several coordinates. So much for 

 the use of the book by students of pure science. As 

 for its use for t he class of students for which it appears 

 to be primarily intended, we can only express the 

 opinion thai the book tends in exactly the same direc- 

 tion as the two German works above reviewed, and 



NO. 2175, VOL. 87] 



we hope it will be as successful as they are in making 

 such students appreciate the value of theoretical know- 

 ledge. 



(4) " Leerboek der Werktuigkunde " ( = Lehrbuch 

 der Werkzeugkunde) is a text-book on elementary 

 statics and dynamics treated without the calculus for 

 use in the Dutch higher schools, and by private 

 students. Both in the methods of treatment and ex- 

 position, and in the worked-out exercises, examples 

 and questions for examination, this book closely re- 

 sembles our numerous English school books on 

 elementary mechanics. Its contents include uniformly 

 accelerated motion, component and resultant velocities, 

 relations between force, mass and acceleration, com- 

 position of coplanar forces and couples, centres of 

 gravitv, ordinary examples on equilibrium of bodies 

 resting against one another, the principle of work, 

 circular and harmonic motion, elementary moments 

 of inertia, impact, and the so-called mechanical 

 powers. This course of study is so familiar to Eng- 

 lish readers that further description is unnecessary. 

 It may be noticed that while the familiar "first and 

 second systems of pulleys " appear in the last-named 

 section, allowance is made for passive resistances, 

 such as friction, which is not always done in English 

 books. On the other hand, the author still follows 

 old customs in trying to deal with composition of 

 velocities without the necessary explicit references to 

 relative velocity, which last receives somewhat meagre 

 attention, a plan which experience shows to lead to 

 frequent mistakes on the part of students. 



G. II. B. 



OUR BOOK SHELF. 

 History of Biology. By Dr. L. C. Miall, F.R.S. 



(The History of Science Series.) Pp. vii+151. 



(London : Watts and Co., 191 1.) Price is. net. 

 This is a wise and instructive book, such as we have 

 learned to expect from Prof. Miall. It is scholarly 

 but restrained, so that the reader is not overwhelmed 

 with too much learning. It is a model of terseness, 

 yet it has that picturesqueness of illustration which 

 is necessary if a history is to grip the ordinary mind. 

 A book like this, which commands our warmest ad- 

 miration, could not have been written except by one 

 who had studied the history of biology for a long 

 time, and at first hand. 



After a brief reference to the biology of the ancients, 

 the long cessation of scientific inquiry that followed, 

 and the revival of knowledge, Dr. Miall sketches the 

 history in five periods. The first (1530-1660) saw the 

 fresh start of botany and zoology, the beginning of 

 experimental physiology, the exploration of new lands. 

 The second (1661-1740) was the period of the early 

 microscopists, of discussions as to the meaning of 

 fossils, of early comparative anatomy .md taxonomy, 

 and of inquiry into the sexes of flowers. The third 

 1741-1789) was the time of Linnaeus and the Jussieus, 

 of Riaumur, of the rise of the genetic or historical 

 method as illustrated by the works of Montesquieu 

 and Buff on, of inquiries into animal intelligence and 

 instinct, the metamorphoses of plants, the function of 

 the green leaf, and so on. The fourth period (1790- 

 1S5S) is illustrated by Sprengel and the fertilisation of 

 flowers, by Cuvier and palaeontology, by Chamisso and 

 alternation of generations, bv von Baer and embry- 

 ology, by the cel'-theory, and by the investigation of 



