October i8, 1894J 



NA TURE 



593 



We will pass over the little incidents of the journey to 

 Jupiter. Suffice it to say that Mars and his moons were 

 observed, that a few asteroids were met and a comet 

 penetrated, and eventually the Callisto — that was the 

 name of the car— was landed on a hard part of the 

 planet's surface. Jupiter was found to be in the Palaeo- 

 zoic period ; and a smattering of geological knowledge 

 has enabled the author to conjure up multitudes of 

 "extinct monsters," which quite eclipse those in Mr. 

 Hutchinson's book. 



Having passed through Saturn's ring, and seen for 

 themselves that it was composed of meteoritic particles, 

 the party arrived safely on the planet. Our belted 

 brother was found to be an abode of spirits, upon the 

 characteristics of which we are not competent to e.\press 

 an opinion. The height of the ludicrous is reached at a 

 dinner given to the travellers by one of these airy 

 nothings, who, we are gravely told, " took only a slice of 

 meat and a glass of claret." The idea of a diaphanous 

 bishop consuming meat and claret is very rich. 



\ word or two on the general character of the book 

 may not be out of place. The author rightly terms his 

 production a romance— that is, a story hung upon seem- 

 ing impossibilities. There is no plot, and the characters 

 are merely mechanical puppets used to expound didactic 

 ideas, so the book cannot be called a novel. It is, in 

 fact, little more than a reading-book suitable for begin- 

 ners in astronomy. We doubt whether many people will 

 read it through without skipping the prosy parts, but 

 they who conscientiously do so will undoubtedly acquire 

 a certain amount of more or less useful knowledge. The 

 author is usually accurate in his astronomy ; and this, 

 considering that writers of romances generally play fast 

 and loose with astronomical phenomena, is saying a 

 good deal. We commend the book to readers who like 

 instructive tales. R. A. Gregory. 



OUR BOOK SHELF. 



Ueher die geometrischen Eigenschaften homogener stwrer 

 Structuren icnd Hire Anwendting attf KrystalU. Von 

 W. Harlow. (Leipzig : Engelmann, 1S94 ) 



rms paper, which was recently published in the twenty- 

 third volume of Groth's Zeitschri/I f. Kfystallograpliie, 

 IS an interesting contribution to the theory of crystal 

 structure. 



Mr. Barlow investigates the nature of a homogeneous 

 structure, by which he means an arrangement of any 

 material of constant form which is uniformly repeated 

 throughout its whole extent. To every point in such a 

 structure correspond other points homologous with it, 

 and these must constitute one of the sixty-five regular 

 assemblages of points as defined by Sohncke in his well- 

 known treatise on crystal-structure. But the symmetry 

 of the structure is not always i:!enlical with that of the 

 .issemblage of points derived from it, and it is sometimes 

 necessary to extend the latter by a geometrical process 

 of reflection or inversion in order to arrive at the 

 symmetry of the structure. This process results in the 

 addition of 164 possible homogeneous structures to the 

 sixty-five already established. Incidentally it is shown 

 that the assemblages of Sohncke are not in reality 

 independent, but can all be regarded as compounded of 

 one or other of ten assemblages belonging to the least 

 symmetrical types in the various systems of crystal- 

 lography. Fedorow and Schonflies have independently 



NO. 1303, VOL. 50] 



advanced a new theory, and agree in the result that there 

 are 230 possible types of homogeneous structure. Since 

 their methods are based upon Sohncke's definition 

 extended by the principle of reflection or inversion, .Mr. 

 Barlow's investigation should lead to the same result. 

 Now he finds 229 types, and expressly states that he is 

 unable to account for a certain one of Fedorow's 

 structures, so that his work is an absolute confirmation 

 of the general accuracy of their calculations. 



When this trifling question of 229 or 230 is settled, the 

 problem of homogeneous structures, which was approached 

 by Hauy 100 years ago, may be regarded as completely 

 soIved//77;« the purely geometrical point of view. 



Mr. Barlow's analysis of Sohncke's assemblages, and 

 his laborious synthesis of the 164 new types, make the 

 relations between the old and the new theory intelligible, 

 and enable the reader to form a mental picture of all 

 these complicated groupings: a task which is by no 

 means easy from the writings of Fedorow and Schonflies 

 without the aid of Mr. Barlow's tables. 



H. A. M. 



Theoretical Mechanics. — Solids. By Arthur Thornton 

 M.A. Longmans' .Advanced Science Manuals. (Lon- 

 don : Longmans, Green, and Co., 1894.) 



The manuals published in this series are written 

 specially to meet the requirements of the advanced stage 

 of science subjects, and the present book will be found a 

 very worthy addition. It is not surprising to hear, as the 

 author tells us in the preface, that in preparing this work 

 he was confronted by the syllabus of this department. The 

 range which these 400 odd pages then cover, can on this 

 account be at once gathered : and it can safelv be staled 

 that the book includes all that is generally necessary for 

 any school course. The order in which the subject has 

 been treated is first kinematics, in which the geomeirical 

 science of inotion is dealt with, then statics, and finally 

 kinetics, in which force is treated in its relation to motion. 

 In each part the author feels himself by no means b lund 

 up as regards the choice of proofs and definitions : and 

 he places before the reader, in a well-arranged series of 

 paragraphs, all the theorems and problems, illustrating 

 them when necessary with clear figures. The real essence 

 of the subject, that is, the " book-work," has had special 

 attention devoted to it, and each chapter contains a 

 special number of problems to be deduced directly from 

 it. Stress has been laid, too, on the importance of solving 

 problems from first principles, and not from a direct 

 substitution in formulae. FormuUu can easily slip the 

 memory, if not totally, then partially, and it is for this 

 reason that numerous methods and samples of solution 

 have been given. 



Examples of all kinds, and especially those introduc- 

 ing great diversity of style, are scattered throughout the 

 work, some being original, while others are obtained 

 from numerous well-known sources. A useful appendix, 

 containing a brief summary of trigonometrical formula;, 

 and a short index, brings the book to a conclusion. For 

 the convenience of those who are preparing the subject for 

 special examinations, a short list is given of the portions 

 which mav be omitted. 



The Earth : an Introduction to the Study of Inorganic 

 Nature. By Evan W. Small, M.A. University Ex- 

 tension Series. (London : Methuen and Co., 1894) 



In this very acceptable addition to the well known Uni- 

 versity Extension Series, we have a sat of chapters which 

 are not intended to form a text-book on physiography, 

 but to serve as a book containing a certain amount of 

 accurate and definite knowledge for the general reader. 

 Such being the case, the author has not dealt fully with 

 any of the various branches, but has treated, in a sketchy 



