August 2, 18S3J 



jVA TURE 



317 



liim to direct his course with confidence towards his point 

 of destination. Whilst, however, giving Mr. Rosser credit 

 for his advocacy, we cannot but regret he has thought it 

 necessary to pad his pamphlet with problems which are 

 in every good treatise on navigation, and with tables which 

 are either useless or are to be found in a more complete 

 form elsewhere. 



In " Stellar Navigation," Problems I. to X. are simply 

 repetitions from works already published, and we notice 

 that in the examples given of obtaining hour angle and 

 azimuth (pp. 9, 10, and 11), Mr. Rosser seems to be 

 unaware of the existence of Raper's tables of logarithms 

 of the log. sine square. Problem XI. is an example of 

 Sumner's method, and is well explained, excepting that 

 we think it far better and quite as quick a process to 

 calculate the azimuth with the hour angle rather than 

 refer to another set of tables. Problem XII. is what is 

 called the new navigation, and is merely another, and in 

 our opinion less simple, way of arriving at the same result 

 as Sumner. Problem XIII., orPaget's method, is merely 

 to attain the position by calculation instead of by plotting 

 on a chart the two circles of altitude, and as this can be 

 done by two plane triangles we should hardly have thought 

 it required explanation. Problem XIV., to compute the 

 altitude of a heavenly body, will be found in all treatises 

 on navigation. 



The Tables A and B are useless, for they are merely a 

 complicated method of finding the error of longitude due 

 to an error of one mile of latitude, which can be readily 

 ascertained by the ordinary traverse-table. Table C, on 

 azimuths, may be, as before stated, as readily and more 

 accurately calculated at the same time as the hour angle. 

 Table D is a combination of two tables invariably given 

 in all treatises on navigation. 



Table I., or mean places of stars, is given in the 

 Nautical Almanac, which every navigator possesses ; 

 Table II. is given more elaborately in Jean's handbook 

 for the stars, which every navigator should possess ; and 

 Tables III. and IV. are given in the Nautical Almanac. 



THE STUDENTS MECHANICS 



The Student's Mechanics. By W. R. Browne. (London : 



C. Griffin and Co., 1883.) 



THIS work, we are told in the Preface, " differs from 

 the many previous works on the subject mainly in 

 the fulness and care with which the foundations" (of 

 mechanics) " have been considered," and it aims at such 

 a treatment of the subject that the student may apply its 

 principles " confidently in attacking questions of practical 

 importance." 



The book is characterised by a considerable amount of 

 original and independent thought, especially in the earlier 

 portion treating of First Principles. This is largely due 

 to the definition of matter which is given :— " Matter 

 consists of a collection of centres of force distributed in 

 space, &c." We are not aware of any writer who has 

 employed this hypothesis to deduce and explain the fun- 

 damental laws of mechanics in an elementary treatise. 

 Nor does it seem to us at all well adapted to elementary 

 students. It is so very important that they should see 

 that mechanics depends, at every stage, in the establish- 

 ment L of its fundamental laws, on experiment, and also 



that they should know what the experiments are and in 

 what way they serve to establish the laws, that the 

 deductive method adopted by Mr. Browne, which does 

 not sufficiently exhibit this connection, would seem to be 

 unsuitable for the purpose he has in view. For though 

 he explicitly states, once or twice, that the science of 

 mechanics rests on experimental evidence, he does not 

 point out the way in which it so rests, nor where the 

 necessity for experiments comes in. As a specimen of 

 his purely deductive method and, at the same time, of 

 poor logic, we have a proof given on p. 9 which reads 

 thus : — " We have defined a force as a cause of motion. 

 Hence we see that, if a force has produced motion, it will 

 be represented to us by the motion it has produced. . . . 

 But motion is measured in terms of velocity. Hence, 

 other things being equal, forces are measured by the 

 velocities which they cause or generate." By the 

 expression " other things being equal " must be under- 

 stood (Art. 30) that "the things they act upon must be 

 equal" (in what respect — of weight, volume, or mass — is 

 not stated, although, from an illustration previously given, 

 we are, presumably, to infer that their weights must be 

 equal). If we substitute (or force, amplitude of vibration, 

 and for motion generated, intensity of illumination, all 

 through the above proof, the reasoning will be equally 

 plausible, and the conclusion false. Of course all that 

 can be inferred from the fact of force having caused 

 motion, apart from experiment, would be that the velocity 

 might be expressed as a function of the force. 



A possible source of much confusion to the student 

 exists in the old-fashioned division of forces adopted in 

 this book into statical, moving, and accelerating forces. 

 The confusion will be increased by the introduction, in 

 addition, of the more modern word " acceleration." In 

 Art. 34S we havey called the acceleration in the formula 

 P = Mf, whilst g is called the accelerating force of 

 gravity ; whilst in Art. 422 the actual tractive force P 

 exerted by an engine on the following train is called an 

 accelerating force. 



The proof in Art. 359 is incomplete, owing to its not 

 recognising the fact that the sum of an infinite series of 

 vanishing quantities may be a finite quantity. 



A valuable feature of the book is the prominence that is 

 given to, and the early introduction of, the theory of the 

 conservation of energy. The friction of machines is de- 

 duced from this principle in a very simple manner. The 

 theorems of statics are very clearly put before the reader, 

 and much that is suggestive and valuable is contained 

 in the articles on elasticity and on the action of railway- 

 brakes. 



The book is one which may be read with profit by a 

 student who is already familiar with elementary mecha- 

 nics and is not liable to be confused by the peculiarities 

 alluded to above, but does not seem to be adapted to 

 students who approach the subject for the first time. 



OUR BOOK SHELF 



Manual of Taxidermy. A Complete Guide in Collecting 



and Preserving Birds and Mammals. By C. J. 



Maynard. Illustrated. (Boston: S. E. Cassino and 



Company, 1S83; London: Tiubner and Co.) 



This small volume of 100 pages of thick paper contains 



the ordinary instructions for skinning, preserving, and 



