July 4. 1895J 



NA TURE 



219 



Chapters xxiv. to xxxiv. may be said to contain descrip- 

 tions of the construction and design of the principal parts 

 of steam enjjines. Some formuhc are given, as well as a 

 few maximum pressures allowable on the different parts. 

 On page 428, the author says that the pressure of 80 lbs. 

 per square inch of bearing surface is allowed in locomo- 

 tive practice between the slide blocks and bars, when both 

 surfaces are of hardened steel. It is not the usual practice 

 to make the slide block surfaces of hardened steel, and in 

 engines built years ago, the pressure per square inch very 

 much e.xceeded this limit. In most recent practice with 

 cast-iron bars and slide blocks, this limit may be safely 

 used. The taking of indicator diagrams is always one of 

 mterest. Chapter .\xv. deals very thoroughly with this 

 subject. Trials in connection with the power and 

 efficiency of engines and boilers naturally follow the 

 indicator, and ver)' complete instructions are given for 

 carrying these out, including precautions in advance of 

 the trial. The concluding chapters of this work deal 

 principally with mill work in its many branches. Friction 

 and lubrication are explained, and many valuaole hints 

 are given. This book should prove of assistance to the 

 steam user. The information given is of such a nature 

 which will appeal to his partial knowledge of the subject, 

 and render him more capable of understanding machinery 

 generally. N J. L. 



LECTURES ON DARWINISM. 

 Lectures on the Darwinian Theory. Delivered by the 



late Arthur Milnes Marshall, M..A., M.D., D.Sc, F.R.S., 



Edited by C. F. Marshall, M.B., B.Sc, F.R.C.S. 



(London : David Nutt, 1894.) 



A LL the characteristics of the late Prof. Milnes 

 -'^ Marshall are strikingly apparent in these lectures. 

 In dealing with the many aspects of a subject which is 

 often imperfectly understood, these lectures are clear and 

 forcible, and the metaphors apt and convincing. 



The first lecture deals with the history of the theorj' 

 of evolution, and contains a concise and interesting 

 epitome of the growth of this great conception, together 

 with a brief account of the chief writers on the subject. 

 The relationship between the process of evolution and 

 the causes upon which it depends are perhaps liable to 

 misinterpretation, the want of any feasible suggestion as 

 to the latter being spoken of as a " fatal flaw " in, or a 

 " fatal objection " to the former. Undoubtedly the want 

 of some efficient cause at first prevented a wide belief 

 in evolution, but logically the two questions are entirely 

 distinct, and the evidence for evolution itself would stand 

 undisputed, even if every one of the causes which now 

 find acceptance were to be abandoned for ever. We know 

 that Darwin himself was a convinced evolutionist long 

 before his discover)- of the principle of natural selection. 



The second lecture treats of artificial and natural 

 selection, and is accompanied by useful figures showing 

 some of the changes which man has been able to 

 accomplish in the creation of his domestic breeds. The 

 whole lecture is clear and telling, the last paragraph 

 being alone liable to possible misconception. In stating 

 that "every species is for itself and for itself alone," it 

 would have been advisable to bring forward instances in 

 NO. 1340, VOL. 52] 



which a species benefits itself by benefiting others. It 

 is most probable that such cases were described in the 

 actual delivery of the lecture. 



Then follow the arguments in favour of evolution, 

 palaeontology being first considered. We here meet, 

 as in many of the other lectures, with exceedingly apt 

 quotations from Darwin, Wallace, and others. It is an 

 unfortunate omission that references are not given. In 

 the deliver^' of the lectures to a general audience they 

 may have been out of place, but there could have been 

 no difficulty in their insertion in the present volume. Here, 

 too, we find many useful figures of some of the extinct 

 forms which are of the highest interest to the student 

 of evolution. The reasons for the imperfection of the 

 geological record are ver)' excellently, and yet briefly, 

 surveyed ; and the same may be said of the sketch of 

 the argument from geographical distribution, in which, 

 however, by an obvious slip, the forest region of Brazil 

 is spoken of as "south of the river La Plata ''(p. 75). 



The argument from embrj-ology was probably the most 

 congenial to the lecturer. This chapter is well illustrated, 

 and contains more detail than the others. The term 

 "acquired or lar^'al characters" (p. 103) is open to ex- 

 ception, and the statement that rudimentary organs must 

 be " inherited, for in no other way can their presence 

 be explained" {loc. cit.), is too brief to be clear. It is 

 probable that this sentence served as a note to be ex- 

 panded by the lecturer ; but it also required expansion 

 by the editor. The chapter will be found extremely 

 interesting and instructive by those who wish to read a 

 popular account of the bearing of embr)'ological facts 

 upon the Darwinian theory. 



The chapter on the colours of animals and plants, 

 although containing much information in a little space, 

 is not worked out in so complete and balanced a fomi 

 as the other chapters, and in large part consists, appar- 

 ently, of notes for the lecturer's use. It is erroneously 

 stated that the colours of certain lepidopterous lar\ae 

 are due to their food, and some of the supposed examples 

 of the direct action of environment are by no means 

 proved to be caused in this way. 



Then follows an interesting lecture on the " objections 

 to the Darwinian theory." The figures of Pteropus on 

 p. 165, although sufficient in themselves, are clumsily 

 arranged. Here, too, many aspects of the subject are 

 only treated in brief lecturers notes, although these 

 frequently contain trenchant remarks. 



The "origin of vcrtebrated animals" is next con- 

 sidered, and the series concludes with an excellent epitome 

 of " the life and work of Darwin." 



It will be seen that the sequence of subjects is a 

 very natural one, and well calculated to lead a general 

 audience to follow and understand the most prominent 

 and important aspects of the Darwinian theory. 



E. B. P. 



OUR BOOK SHELF. 



My Climbs in the Alps and Caucasus. By .A.. F. 



Mummer)'. Illustrated. (London : T. Fisher Unwin, 



1895.) 

 Mr. Mummery is a bold man. Not only has he 

 dared greatly among peaks and glaciers, but also 

 he does not scruple to declare that he enjoys mountain 



