October i i, 1906] 



NA TURE 



58: 



in which in eloquent words Abbe traces the debt of 

 <)[)liiians to that great man. 



At some future day a pupil of Abbe's will carry 

 <>n the story and show how the next great advance in 

 j)ractical optics was the work of Abbe himself. His 

 friends have done well to collect with loving care these 

 writings of their master, and we who know him 

 chiefly through his works are grateful to them for 

 ihe manner in which they have discharged their task. 



OVR BOOK SHELF, 

 ilagnetische Kraftfelder. By H. Ebert. Secona 

 edition. Pp. .\ii + 4is. (Leipzig: J. A. Barth, 



1905.) Price 7 marks. 

 This is a second edition of Prof. Ebert's well known 

 treatise on magnetic fields of force, which first 

 appeared in 1902. The author handles his subject as 

 before with a wealth of illustration, and with a 

 theoretical grasp, which make the book valuable alike 

 to student and teacher. Indeed, the teacher will find 

 in its pages many useful suggestions. Of these is 

 the magnetic vane of Jaumann, depicted on p. 23, 

 A'hich recalls the appliance of Petruscheffsky, in which 

 rt small bar magnet was suspended through one pole, 

 with a counterpoise to make it lie horizontally, and 

 act as a one-pole magnet. Again, the little frame 

 depicted on p. 29 for holding bar magnets during the 

 operation of manufacturing their filing figures on a 

 ■sheet of glass above them is worthy of notice. The 

 .author adopts as a brief synonym for " a point in a 

 (nagnetic field to which we direct our attention " 

 Boltzmann's term " Aufpunkt," for which we have 

 110 English equivalent. On p. 206 he uses the term 

 ■" Billiontel " for 10-', which is surely a slip, since 

 in German, as in English, a billion is 10'", not 10'. 

 On p. 54 his definition of unit pole is that it is such 

 as to repel with a force of i dyne a similar pole when 

 at a distance of i centimetre apart in vacuo, whereas 

 hitherto the accepted definition has been when in air. 

 The difference may be unimportant, but it should not 

 pass without challenge. In this edition the author 

 has cut out most of the section upon cyclical systems, 

 and certain deductions of the Maxwell-Hertz equations 

 which were formerly included. On the other hand, 

 he has introduced new matter relating to the electronic 

 view of electricity in its relation to magnetism and 

 to the Zeeman phenomenon. While this part of the 

 book has been shortened, there have been added at 

 the end fresh sections on induction, on the magnetic 

 circuit — a distinctly valuable chapter — and another 

 of lesser merit on dynamo-machines. The author 

 erroneously attributes to Pixii, on p. 359, the inven- 

 tion of the split-tube commutator. What Pixii used 

 in 1832, on the suggestion of Ampere, was the 

 divided mercury-cup familiar to electricians in the 

 (jrimitive motors of Ritchie. 



It is distinctly interesting to find a summary of 

 recent work on kathode rays, Becquerel rays, and the 

 rays emitted by radium, appearing as an integral part 

 of a chapter which opens with the action of the 

 magnetic field upon a movable conductor carrying a 

 current. The doctrine of the electron appears to be 

 thoroughly accepted as an essential part of electro- 

 magnetism. But the definitions which the author 

 gives on pp. 157 and 158 of an electron apparently 

 exclude anything and everything that is not actually 

 moving with a high velocity : — " Unter Elektron hat 

 man die sich mit grosser Geschvvindigkeit bewegende 

 negative Elementarladung zu verstehen." Is an 

 electron not an electron when it is at rest? 



S. P. T. 



NO. 1928, VOL. 74"! 



Inheritance in Poultry. By C. B. Davenport. Pp. 

 V+134. (Washington, D.C. : The Carnegie Institu- 

 tion, igo6.) 

 This is a valuable addition to the rapidly-increasing 

 literature dealing with the subject of inheritance. It 

 affords a good example of the growing complexity 

 of the theories which have been founded on the 

 famous discovery of Mendel. The simplicity of the 

 original Mendelian .system has now to be supple- 

 mented by such conceptions as those of " imperfect 

 dominance," " incomplete segregation," " compound 

 allelomorphs," and the like. The author of the pre- 

 sent treatise, well known as the director of the 

 station for experimental evolution at Cold Spring 

 Harbour, New York, deserves much credit for the 

 care with which his experiments have been devised 

 and their results recorded. Each e.xperiment is 

 methodically described under the heads of " Statement 

 of Problem," "Material," "Results," "Con- 

 clusions," and the general bearing of the whole series 

 on evolutionary theory receives full and candid dis- 

 cussion in a final section. The author's standpoint, 

 as was to be expected, is in the main Mendelian, but 

 he recognises the facts that both dominance and re- 

 cPssiveness are frequently incomplete, and that " an 

 adequate theorv of gametic purity has not only to 

 explain the simple Mendelian formula, but also the 

 facts of imperfect dominance, impurity of extracted 

 forms, latency and atavism, and occasional particulate 

 inheritance." Prepotency (in Bateson's sense) he 

 holds to be as truly important in inheritance as 

 dominance. It is worth noting that de Vries's dictum 

 as to the sharp separation of the constituent units 

 which make up the characteristics of organisms, 

 between which units transitions exist " as little as 

 between the molecules of chemistry," is, in the 

 author's opinion, not borne out by the present experi- 

 ments; nor does he find confirmation of the same 

 biologist's assertion as to the different modes of in- 

 heritance of " specific " and " varietal " character- 

 istics. 



There are a few marks of carelessness in the text, 

 as where the birds represented by Figs, i and 2 are 

 spoken of as " black -crested white Polish." The 

 plates are generallv admirable, but in the absence of 

 colour it isdifficult to distinguish between true white 

 and reflected high lights — a point which in some cases 

 is of great importance. F. A. D. 



German Scientific and Technological Reader. Book 

 i., pp. ix+105; Book ii., pp. viii+115. By E. 

 Classen and J. Lustgarten. (London and New 

 York : Harper and Brothers, igo6.) Price 2S. net 

 each. 

 These two books should serve a useful purpose in 

 familiarising students of science who are anxious to 

 read scientific works in the German language with 

 expressions and terms common in such works, but 

 not to be found in school-books. Both volumes con- 

 sist of descriptive accounts of principles and proper- 

 ties relating to various departments of science, and 

 of technological processes, plainly printed in Roman 

 characters, and suitable for reading by students who 

 know the rudiments of German grammar. 



The descriptions in the first volume deal with the 

 propaedeutics of physical and chemical science, dye- 

 ing, metallurgy, electrotechnics, and engineering; 

 and those in the second volume are concerned, in 

 addition, with some special points in physics, chem- 

 istrv and chemical technology, spinning and weaving, 

 and brewing. There is a vocabulary in the first 

 volume, but not in the second, which is somewhat 

 more advanced, and requires the use of a dictionary. 



