Algust 5, 1909] 



NA TURE 



157 



The subject-matter treated includes such applications 

 as the instantaneous centre of a connectinfj rod, two- 

 speed gears, and the elements of dynamics of rotation. 

 There are many reasons why the latter subject should 

 be included in an elementary treatise; indeed, the 

 authors claim that, " frankly, unless a student means 

 to know, in broad outline, about as much of the 

 principles of mechanics as we have given, he may 

 with advantage allot more time to some other 

 subject." 



In certain details the book leaves something to be 

 desired. It would surely be better, for example, to 

 give the rule for composition of relative velocities 

 after, instead of before, the construction for the rela- 

 tive displacement and velocity of two moving bodies. 

 The present order is a survival of the old idea that 

 because the parallelogram of forces is the fundamental 

 proposition in statics, the parallelogram of velocities 

 ought to be the fundamental proposition in kine- 

 matics. In the proof of the relations between angular 

 1 and linear velocity, a 60 is introduced unnecessarily 

 and then cancelled by considering the space described 

 in a minute instead of in the unit of time (a second) 

 assumed in the definitions. In several places where 

 uncertainty exists as to how much should be included 

 in the text and what should be omitted, the final result 

 suggests that the authors were not given sufficient 

 facilities for making alterations when the proofs were 

 in type. The paragraphs are unnumbered, and this 

 is a great drawback, but the worst feature is the 

 illustrations, which are badly reproduced, with coarse, 

 unsightly lettering. In one of them, on p. 177, a 

 capital V looks like a Greek 7. If books of this 

 class are to hold their own in the field of competition, 

 not only should the figures be above reproach, but a 

 large amount of time and thought must be devoted 

 to minor alterations and emendations such as only 

 suggest themselves when the text has been seen in 

 print. 



(2) If novelty and originality is one of Mr. Jackson's 

 strong points, this cannot be said of Prof. Jessop and 

 Dr. Havelock's book. It brings back to memory days 

 of long ago, with its " forces of i, \l 2, and *'j lbs.," 

 its Roman and Danish steelyard, its three classes of 

 lever, the oar being included in the second regard- 

 less of the man's thrust on the rowlock, its mechanical 

 advantage instead of the more modern velocity ratio 

 and efficiency, its systems of pulleys which only 

 lift a weight a small fraction of the height of the 

 supporting beam — and perhaps do not lift it at all 

 if the ropes are extensible, and its Attwood's machine 

 neglecting inertia of pulley, in the first instance, 

 although this is now taken into account at the end 

 of the book. But Jessop's " Elements of Applied 

 Mathematics " was an excellent book when it was 

 written, and it is not the book which has gone back- 

 ward in its present revised edition, only other people 

 have moved forward. Moreover, the present reviewer 

 can ill afford to find fault with an author who is pre- 

 vented by his professorial duties from completely re- 

 writing his text-books when his opinions on certain 

 points have changed. At the same time, in view of 

 the fact that revision has been undertaken by Prof. 

 Jessop's lecturer, we think something more might 

 NO. 2075, VOL. Si] 



have been done. The separate formulae for the re- 

 sultant at angles of 30°, 45°, and 60° might surely 

 be struck out now, although the present reviewer 

 pleads guilty of having perpetrated the same bar- 

 barisms (under protest] when he was younger and 

 was informed that certain classes of students required 

 them. On the other hand, the addition of sections 

 on harmonic motion, bending moment, and shearing 

 force (under graphical statics), and the chapter on 

 energy of rotating bodies are valuable additions. In 

 the latter chapter the moments of inertia of simple 

 figures are stated without proof. Perhaps this is the 

 best way, in view of the fact that integral calculus is 

 now usually taught at an early stage ; had this not 

 been the case, the use of the geometric progression 

 formula for making the necessary summations w'ould 

 have been recommended. 



A student might do worse than use Prof. Jessop's 

 book for algebraical drill, supplementing it by a course 

 of experimental mechanics, or by Mr. Jackson's book; 

 and whatever else may be said, no exception can be 

 taken to the general appearance of the book, or the 

 diagrams, which fully maintain the high standard 

 that characterises Messrs. Bell's text-books. 



OVU BOOK SHELF. 



The State and the Farmer. By Prof. L. H. Bailey. 

 Pp. xii-l-177. (New York: The Macmillan Co.; 

 London : Macmillan and Co., Ltd., 1908.) Price 



Less than a generation ago farming and farmers 

 made verv small figures in the public eye ; men of 

 affairs, when they gave the subject a thought, regarded 

 I3ritish agriculture as a dying craft, something that 

 had ceased to pay and miglit be left to extinguish 

 itself quietly, leaving the country for the recreation 

 of the town-dweller, to provide sport for the rich in. 

 dustrial, health and the gratification of his jesthetic 

 tastes for the employee. Business men paused some- 

 times to make pharisaical remarks about the wasteful- 

 ness of the farmer; men of science scolded him for 

 sticking to his old ways, not adventuring his substance 

 on the crude generalisations which were put forward 

 to represent the infinitely complex life of animals and 

 plants ; the politician had no use for the agriculturist, 

 whose vote he knew was safe in the landlords' pockets; 

 and the journalist saw little but comic copy to be got 

 out of Hodge and its ways. As Sir Horace Plunkett 

 said in his British Association address, modern 

 civilisation has joined the rural exodus. 



But latterly there have been signs of change; the 

 triumphal march of industrial progress, with its con- 

 comitants of vaster factories and ever extending 

 suburbs of mean streets, has proved less satisfying 

 than its prophets had promised; the nation has begun 

 to awake to the essential instability of such a system, 

 and to the need of keeping up agriculture as the 

 soundest basis of the State and the only means of 

 creating wealth, whether of men or things. 



To some men the necessity of drawing men back 

 to country life seems little less than a holy cause 

 into the service of which they are ready to put their 

 whole strength, and among such men Prof. L. H. 

 Bailev, of Cornell, is perhaps most prominent on 

 the other side of the Atlantic. In the little book before 

 us Prof. Bailey pleads for the better organisation of 

 rural life with eloquence and conviction; rural life, not 

 merely because it pays, but because it is the life best 

 worth living, most calculated to raise a sober and 



