April 28. 1910] 



NA TURE 



243 



this becomes an artificial science or a simple abstrac- 

 tion. Would it not, however, be equally correct to 

 describe dynamics as an "artificial science or simple 

 abstraction " because it deals only with what -would 

 happen if certain existing resistances were absent? 



The subject-matter extends up to and including 

 couples, circular motion, a little about properties of 

 matter, such as elasticity and ballistics, and a final 

 paragraph dealing with Jules Verne's hypothetical 

 voyage to the moon. 



It is not to be denied that "philosophy of science" 

 is much more studied in France than in this countrj-. 

 It also appears that the book is primarily written for 

 those who have to teach children rather than for the 

 children themselves. All we can say is that a course 

 of instruction based on this book would in all prob- 

 ability be far above the heads of English children of 

 the ages contemplated. 



(4) \\hile Prof. Tesar has " said his own say " in 

 his preface and metaphysical appendix, his object in 

 the rest of the book has been to present the principles 



jof mechanics in a clear and intelligent form, and to 

 : employ practical illustrations as far as possible. In 

 1 both these aims he appears to have been very success- 

 ful. He is careful to distinguish between forces 

 l(Krafte") and force effects (Kraftauszerungen), pointing 

 iout that the parallelogram law applies to the latter, 

 'and that its truth for any physical vector quantities 

 lis based on experience. His readers should learn to 

 ■ discriminate clearly between the formal rational 

 I dynamics and its applications to the practical study 

 jof mechanics. For want of this distinction the whole 

 jsubject in less careful hands often becomes more 

 I appropriately describable as dogmatics. The prac- 

 tical illustrations are very instructive and suggestive. 

 How many who have taught rigid dynamics have 

 thought of working out the condition whether a bell 

 iwill or will not ring when it is swung? The author 

 gives practical calculations for a bell in Cologne 

 iCathedral cast from the cannon captured in the 

 Franco-Prussian War, which failed to ring until its 

 jclapper was altered in length. 



(5) -As has been previously pointed out in reviews, 

 'Prof. Foppl's treatises on technical mechanics are of 

 ia far more advanced character than the mechanics 



taught commonly to technical students in this 

 .country. Vol. iii., which includes a large portion of 

 jthe mathematical theory of elasticity, now reaches us 

 iin its fourth edition. The new volume, "The Most 

 Important Studies of Higher Dynamics," deals with 

 irelative motion, systems with several degrees of 

 Ijfreedom, in particular compound pendulums, includ- 

 ing the bell and its clapper, the gyrostat, and an out- 

 jline of hydrodynamics. Under the gyrostat we have 

 ija detailed discussion of Schlick's ship governor, and 

 hfin a circular issued with the book we are asked to 

 point out that the Brennan mono-rail came too late to 

 be included in the book, a short note at the end being 

 all that was possible, as the whole of the. text was 

 already in print. It is, however, pointed out that the 

 theory of the Schlick gyroscope is applicable with 

 slight modifications to the mono-rail, some terms 

 occurring in the equations having merely to be re- 

 NO. 21 13, VOL. 83] 



versed in sign. Thus an interesting exercise is pro- 

 vided for those possessing the necessary mathematical 

 knowledge, to go over the work introducing the 

 necessary changes, and doubtless the next edition will 

 see them in the text. G. H. Bryan. 



HARDY TREES AND SHRUBS. 

 Trees and Shrubs of the British Isles, Native and 



Acclitnatised. By C. S. Cooper and W. P. Westell. 



Vol. i., pp. xxxii + lxxxiv+108; vol. ii., pp. viii + 261; 



78 full-page plates by C. F. Newall. (London : J. 



M. Dent and Co., 1909.) Price, two vols., 215. net. 

 A MID the torrent of books on gardening with 

 ■^ *■ which a patient public has been deluged during 

 recent vears, we have searched in vain for a really 

 comprehensive and authoritative work on hardy trees 

 and shrubs. Of mere book-making there has, of 

 course, been no end. It is so easy to sit at a desk and 

 boil down from Loudon, Sargent, &c., and from the 

 copious literature in horticultural journals, sufficient 

 to make a respectable-looking volume, without ever 

 taking the trouble to turn over a leaf or dissect a 

 flower on one's own account. But this method has 

 its disadvantages. The same stale old errors are 

 once again repeated, and to them our new author 

 must, perforce, add some of his own. There has been 

 too much of this kind of tree literature in the past, 

 and it was with a feeling of pleasant anticipation that 

 we turned to these two handsome volumes in the hope 

 that a work had at last been written worthy of the 

 subject. 



That it marks a considerable advance on much that 

 has app>eared is certain, but its scof>e is sorriewhat 

 limited, and the authors do not appear to us to have 

 done the best that could have been done within the 

 limits they set themselves. British trees and shrubs 

 are done thoroughly and well, and those portions 

 dealing with them constitute the most valuable part 

 of these volumes. When the authors deal with what 

 they term " acclimatised," as distinct from native, 

 species, their work often suggests the study and 

 the bookshelf, rather than the open air and the living 

 tree. For it is bv no means free from error, and at 

 times shows a lack of intimate knowledge of the 

 plants dealt with. 



The book op>ens with an introduction in which the 

 general subject is discussed pleasantly and sug- 

 gestiveh'. It is an attempt to interest the hitherto 

 uninterested reader, not only in the more evident 

 beauties of leaf and flower, but to get him also to 

 appreciate those profounder beauties of trunk and 

 branch and bud which we are afraid the average 

 reader often does not discern, but which make the 

 leafless woods in their season as full of delight to 

 the real tree-lover as the full leafage of June. This 

 part of the work was well worth doing and is well 

 done. 



Some fifty or sixty pages are then devoted to the 

 discussion of injurious and useful insects, galls, and 

 fungoid pests, with directions for the composition anH. 

 application of various remedies. This, although use- 

 ful, is too liberal an allowance for such subjects in a- 



