May 19, 19 10] 



NATURE 



335 



knowledge of the fundamental facts has now become 

 sufficiently definite to justify the step, Dr, McClung 

 has arranged a series of experiments designed to give 

 a practical knowledge of the methods employed and 

 the results obtained in these newer developments of 

 electrical science. The description of the book as a 

 text-book with experiments indicates the plan on 

 which it is written. A connected account of the sub- 

 jects considered is given from an experimental point 

 of view-, with descriptions and diagrams of suitable 

 apparatus by means of which students may perform 

 the experiments and test the results stated, without 

 unnecessary complications. Thus the book provides a 

 convenient summary of the results of recent re- 

 searches, and is not a volume for the laboratorv onlv. 



The book is divided into two parts ; chapters i.-vii. 

 deal with electric discharges through gases, and 

 chapters viii.-xvi. with radio-activity. In part i. 

 accounts of kathode and Rontgen rays and a sketch 

 of the ionisation theory are given, while descriptions 

 of a few experiments on ionisation by ultra-violet 

 iight and by incandescent solids are added. We com- 

 mend to the notice of those beginning research in 

 this department the valuable chapter on the apparatus 

 and instruments used in the investigations. The 

 practical hints on the manipulation of electrometers 

 and electroscopes, given by an experienced worker, 

 cannot fail to be helpful. In part ii. experiments on 

 the radiations and emanations from radio-active sub- 

 stances, on induced activity, and on the radio-activity 

 of the atmosphere are described, and a sketch of the 

 disintegration theory is added. A list of 125 experi- 

 ments is given at the beginning of the book ; the 

 author suggests that the more difficult experiments, 

 of which twenty are indicated, may be reserved by the 

 student for a later stage. 



We think that students contemplating research in 

 these branches of physics would find the course a 

 valuable preparation for their work. From the nature 

 of the experiments, however, it will be evident that 

 most of them could be undertaken profitably only by 

 those who, as a result of their previous experience of 

 practical work in electricity, have acquired consider- 

 able skill in manipulation ; for it would be useless to 

 set a student who was unable to manage a galvano- 

 meter to struggle with the difficulties of an electro- 

 meter. To set up the apparatus and perform the 

 whole of the experiments would require a considerable 

 time ; but a student who worked through even a small 

 number of experiments selected from the list would 

 gain a valuable insight into the methods of investiga- 

 tion in use in this part of the subject. The provi- 

 sion, ]or purposes of instruction, of the apparatus 

 which is necessary would, we fear, form a difficulty 

 iR some physical laboratories, and, paradoxical as it 

 may seem, not least in those in which researches 

 dealing with the subjects of the book are in full pro- 

 g^ress. 



A few of the definitions in the theoretical sections 

 require more careful statement, and the remarks on 

 the law of decay at the end of chapter xii. need 

 revision. The book is also capable of considerable 

 improvement in literary style. 

 NO. 2 1 16, VOL. 83] 



TWO BIOLOGICAL TREATISES. 



(i) Die Selektionstheorie. Eine Untersuchung von 

 August Weismann. l*p. vi+69. (Jena: (iustav 

 Fischer, 1909.) Price 2 marks. 

 (2) Experimentelle Studien zur Soma- und Gesch- 

 lechts-Differenzierung. Erster Beitrag. Von Prof. 

 Johannes Meisenheimer. Pp. vii+149. (Jena: 

 Gustav Fischer, 1909.) Price 6.50 marks, 

 (i) A MONG the most welcome effects of the Dar- 

 l\ win commemoration held last year at Cam- 

 bridge has been the reappearance of Prof. Weismann 

 in the lists as a champion of the doctrine of natural 

 selection, a cause which for the last fifty years he 

 has never ceased to defend with the whole weight of 

 his authority and learning. But for the invitation 

 from Cambridge to contribute to the memorial volume 

 published on that occasion, the veteran professor, as 

 he informs us in the preface to his "Selektions- 

 theorie," would scarcely have undertaken to add any- 

 thing to his former writings on the subject. Now, 

 however, he has not only enriched the Cambridge 

 " Festschrift " with the English essay in which his 

 views are so admirably stated, but he has published 

 the same treatise in German, substantially unaltered, 

 but with the addition of certain passages in which 

 j his conclusions on the subject of the reality of the 

 selection-process are driven home with fresh force 

 and cogency. 



In this production Weismann 's dialectical ability 

 and literary skill shine out as conspicuously as ever; 

 and it would be difficult to find, within the same 

 compass, an equally convincing presentment of the 

 case for Darwin's conception of the action of natural 

 selection in the formation of species, or one more 

 aptly illustrated by examples drawn from many 

 departments of organic nature. While so much con- 

 tinues to be written which tends to overcloud and 

 confuse the simplicity of the Darwinian position, it is 

 refreshing to see how Weismann goes straight to 

 the point, brushing aside those objections that pro- 

 ceed from imperfect appreciation of the facts to be 

 explained, and quietly putting in their proper place, 

 as subordinate to the selection-theory, certain well- 

 attested phenomena which have in some quarters 

 been supposed to be hostile to Darwinian interpreta- 

 tions. All this is done with the utmost candour and 

 courtesy, and without the least trace of arrogance or 

 contempt for adverse opinion. In full agreement with 

 both Darwin and Wallace, Weismann here holds, as 

 he has always done, that adaptation is a universal 

 principle in the world of life, and that of this prin- 

 ciple selection affords the one and only possible 

 explanation. After reading the masterly defence of 

 the position to be found on pp. 48-69 of the pre- 

 sent treatise, those younger biologists who may have 

 allowed themselves to be troubled with doubts as to 

 whether, after all, the theon,- of adaptation by selec- 

 tion has not been overdone may well take fresh 

 courage and renew their confidence in Darwin's solu- 

 tion of the teleological problem. 



Sexual selection, to which Darwin attached much 

 importance, has been vigorously attacked from many 



