August 20, 1903] 



NATURE 



365 



students whose abilities and opportunities are limited; 

 but such students will probably not possess sufficient 

 g^rasp of the mathematical principles to enable them 

 to apply their knowledge to any new problem. Their 

 training is " technical " in the English sense of the 

 term. It may be questioned whether the German view 

 of technical physics, as understood by the author of 

 the present work, is not really the wiser and the more 

 likely to lead to sound educational and commercial 

 progress in the end. 



The book begins with a general chapter on the 

 geometry of motion. The idea of time is introduced 

 in the next chapter on velocity and acceleration. This 

 is followed by a chapter on relative motion, treating 

 the usual examples, such as projectiles, planets, pen- 

 dulum, oscillations, &c., in a very general manner. 

 In chapter iv. we have mass and force introduced 

 together with friction, damped oscillations, impact, 

 work, and kinetic energy. In chapters v. and vi. we 

 have a general discussion of the equations of motion 

 in a plane, and in three dimensions, respectively, with 

 a number of important applications, such as the theory 

 of the precession of the earth's axis, the centrifugal 

 governor, and the theory of models and dimensions. 

 The book concludes with a historical survey of the 

 * evolution of mechanical science divided into three 

 sections : — (i) before Newton, (2) from Newton to 

 Lagrange, (3) the later development of technical 

 mechanics. This historical excursus would be un- 

 necessary, from the teacher's point of view, for the 

 mere inculcation of the principles of the subject, and 

 would interfere with the logical order of ideas. But 

 from the student's point of view such a historical 

 survey is not only extremely interesting, but also most 

 instructive. Correct ideas can only be appreciated in 

 their true significance by contrast with incorrect con- 

 ceptions, such as abound in the earlier history of the 

 subject; and the methods and principles at which we 

 have arrived at the present stage of progress are not 

 in all probability the best expression of the science, 

 but are the outcome of an intricate process of evolu- 

 tion along certain lines. To appreciate them fully it 

 is necessary to know something of the manner in 

 which they have been evolved. 



It is probable that the English engineer would hesi- 

 tate before devoting much time to the study of a 

 foreign text-book which at first sight is of so " un- 

 practical " a nature. But the mere existence of the 

 book in its present form suggests a lesson which our 

 technical educators may have yet, in some cases, to 

 learn. H. L. C. 



OVR BOOK SHELF. 



An Introduction to Botany. By W. C. Stevens. Pp. 



428; with preface and index and key, 121 pp. and 



index. (New York and London : D. C. Heath and 



Co., 1903.) Price 6s. 



Among the numerous works professing to guide the 



elementary student through the mazes of botanical 



science, this may claim several advantages, inasmuch 



as the greater part of the book is based on a sound 



( onception of the method best suited for the purpose 



nf training the beginner to observe and think for him- 



M'lf. It is the method which Huxley worked so hard 



i'> introduce into this country many years ago, 



namely, that of encouraging the student to invcsti- 



NO. .1764, VOL. 68] 



gate first, and then telling him more about the things 

 he has seen, keeping the opinions and records of others 

 in the background until he has acquired a stock of 

 his own knowledge to work upon. 



On the whole the purpose of the book is carried 

 out, but the figures are often very poor, and the part 

 dealing with systematic botany frankly returns to the 

 old lines, and is, moreover, only suited to American 

 students. Why this part should be separately paged 

 is not clear; it necessitates a second index, and makes 

 the book somewhat cumbrous. English students will 

 find far better exercises in the use of analytical keys 

 and floristic work generally in Hooker and Bentham's 

 well-known " Flora." 



Kant's Lehre vom Glauben. By Ernst Sanger. Pp. 



xvii+170. (Leipzig: Verlag der Durr'schen Buch- 



handlung, 1903.) Price 3 marks. 

 Kant's philosophy has found, and continues to find, 

 various application and still more various interpret- 

 ation. The diversity of commentaries has led, in some 

 quarters especially, to a feeling that Kant has re- 

 ceived enough development, that in some cases the 

 development has been too much controlled by the ideas 

 of later systems, that, in fact, we must go back to 

 Kant and define more clearly our ideas of what he 

 really said. The present essay is obviously designed 

 to assist that process. If we except the last section, 

 which makes reference to the relation between Kant's 

 doctrine and theology, the entire essay is confined to 

 collecting Kant's statements and piecing together his 

 doctrine of belief from the original sources. The 

 author has clearly spared no pains to make his collec- 

 tion of passages complete, nor has he failed to point 

 out the significance of Kant's distinctions or his 

 variations in the use of terms. For the purpose in- 

 dicated, it was necessary to follow the historical order; 

 the result is a monograph not, perhaps, eminently 

 readable, but deserving study. Though the author's 

 reference seems to be especially to that scientific 

 theology which ever finds it a primary duty to accept 

 or answer Kant, his essay cannot fail to be of value 

 to all interested in philosophy. His remarks on the 

 various passages show clearly how the doctrine of 

 belief runs through all Kant's work, and how its 

 elucidation throws light on the structure and purpose 

 of all his writings. An introduction by Prof. ur. 

 Hans Vaihinger will doubtless appear to many an 

 adequate recommendation. G. S. B. 



Elementary Physics. Practical and Theoretical. 

 ' Second Year's Course. By John G. Kerr, M.A., 



LL.D., and John N. Brown, A.R.C.Sc. (Lond.). 



Pp. 169. (London: Blackie and Son, Ltd., 1903.) 



Price 2i-. 

 Th»^. practical exercises here brought together are in- 

 tended for young students who have already had a 

 year's work in experimental physics. Dynamics, heat 

 and light are the only branches of the subject drawn 

 upon, and presumably the learner is expected to wait 

 until his third year before he may hope to become 

 acquainted, from his own experiments, with the funda- 

 mental principles of sound, electricity, and magnetism. 

 The exercises are well arranged and the instructions 

 given are sensible and helpful, and show that the 

 authors are teachers of experience. The student is 

 more likely to obtain good results if a simple sighting 

 apparatus is used in counting vibrations of the pendu- 

 lum, but no instructions appear to be given as to the 

 use of one. On p. 64 the student is told to hang a 

 50-gram weight to a thread for use in his experiment, 

 which necessitates handling the weight, a bad habit 

 which the teacher should discourage as much as 

 possible. A want of uniformity in the spelling of 

 gram should be corrected in the next edition. But, 

 on the whole, the book is likely to prove useful. 



