July 30, 



1 908 J 



NA TURE 



291 



published works : — " If the interferometer is not in ad- 

 justment, see instructor," for example. On the other 

 hand, there ars few slips, though Joule's experiment 

 is credited to Thomson and Joule, and few typo- 

 graphical errors, though proper names are badlv 

 mangled. 



The great defect of the book as a book for students 

 is due to the fact that its aim is low. As hard think- 

 ing and independent thinking are essential features 

 of any college discipline worthy of the name, a book 

 the chief aim of which is to enable students to acquire 

 skill in making measurements, though it may be 

 useful for certain classes of technical students, could 

 not be made a good book either for students generally 

 or for the higher grades of technical students. 



The chief merit of the book is the excellence of the 

 advice it embodies as to the details of laboratory prac- 

 tice. From the authors' point of view procedure is of 

 prime importance ; and as a reference book on points 

 of procedure their manual will be found useful even 

 in old-fashioned laboratories which still aim at 

 Pickering's ideal. 



A STUDY OF THE MOON. 

 La Terre et la Lune : Forme extirieure et Structure 

 interne. By P. Puiseux. Pp. 176. (Paris : 

 Gauthier-Villars, 1908.) Price 9 francs. 

 A BOOK which seeks to throw light on terrestrial 

 xV evolution from a study of the moon must possess 

 considerable interest to both geologists and astro- 

 nomers. But we may prophesy that this book will 

 be more welcomed by geologists than by astro- 

 nomers, or, at any rate, by mathematicians. For 

 M. Puiseux, disregarding somewhat lightly the 

 weighty dynamical reasons which have been brought 

 forward by Kelvin and Sir George Darwin, among 

 others, in favour of a solid interior to the earth, 

 throws in his lot with those geologists who support 

 the theory of a thin crust surrounding a liquid interior. 

 He bases his argument partly upon purely terrestrial 

 phenomena — and here we must frankly admit that we 

 do not find his reasons convincing — and partly upon 

 analogy from the moon. M. Puiseu.\ points out many 

 interesting points of resemblance between the general 

 configuration of the earth and some of the principal 

 features of the moon's surface; and his argument 

 that the moon's surface, having sufTered but slightly 

 from the action of water, can throw light on a stage 

 of development through which the earth has passed 

 has much to recommend it. But we fail to follow him 

 in the further arguments that he brings forward to 

 prove that it is only the reaction of a liquid interior 

 on a gradually thickening crust which can have pro- 

 duced the effects which are now to be seen on the 

 moon's surface. 



M. Puiseux is on less controversial ground when he 

 discusses the order of development of the various 

 types of marking on the lunar surface. The careful 

 study which he has made of the face of the moon 

 compels special attention to be paid to his views on 

 this subject, and many of his conclusions command 

 the reader's assent. The probable origin of the lunar 

 craters is particularly well discussed, a strong presenta- 



NO. 2022. \"OL. zZL 



tion of the case for volcanic origin being given. In 

 this connection we cannot forbear to quote the delight, 

 ful sentence with which M. Puiseux closes his discus- 

 sion of the question. Speaking of two humps, sur- 

 vivors of what in his view was the primitive form of 

 the crater, he says : — 



" II semble que Ton doive regarder ces rares temoins 

 d'image disparu avec un peu de cette veneration que 

 Ics archcologues ressentent en face des m^dailles 

 antiques." 



The discussion of the past history of the moon's 

 surface and of the relations between the different types 

 of markings is illustrated by a fine selection of en- 

 largements of the Paris photographs of the moon ; 

 these help materially to emphasise M. Puiseux's con- 

 tention that the photographic method is markedly 

 superior to the older methods of studying the moon's 

 surface. Perhaps we may suggest that it would 

 render the photographs more useful to the general 

 reader if the special features of interest which they 

 present, and to which attention is directed in the text, 

 were more clearly marked. 



Each of the subjects dealt with in the book contains 

 an interesting historical account of the theories and 

 speculations that have from time to time been put 

 forward. The older speculations are fully discussed, 

 but there are several notable omissions of recent work. 

 For instance, the discussions on the pear-shaped earth 

 by Profs. Jeans and Sollas surely deserve consideration 

 quite as much as Lowthian Green's tetrahedron, 

 .^gain, Prof. Love's spherical harmonic analysis of the 

 earth's surface should also be considered in any com- 

 plete account of speculations on the figure of the 

 earth, while some reference surely ought to have been 

 made in the book to the planetesimal hypothesis of 

 Profs. Moulton and Chamberlin. 



There are one or two further omissions that must be 

 noted. For instance, there is no reference to the need 

 for revision of the present method of naming objects 

 on the moon's surface, such as one not unnaturally 

 looked for from a member of the international com- 

 mittee engaged in considering such a revision. Again, 

 the earlier illustrations of the book would be brought 

 into closer contact with the text if a more detailed 

 account of modern geodetical methods were added. 

 This could be done without overweighting the book. 



There remains the never grateful task of pointing 

 out some errors that have slipped into the work. Thus 

 the statement on p. 88 that the physical libration and 

 the elongation of the moon along the axis pointing to 

 the earth have never been determined by observation 

 is inaccurate; it shows neglect of the results obtained 

 bv Dr. Hayn. A further statement on p. gi about 

 libration suggests that the author is confusing the 

 forced physical libration with the free or unforced libra- 

 tion, which has not been surely determined. Again, on 

 p. 100, .Sir George Darwin's earlier estimate of the 

 rate of rotation of the earth when the moon separated 

 from it is given instead of his later estimate, 2h. 24m. 

 But these errors can easily be remedied in the second 

 edition, for which the interest of the subjects dealt 

 with in the book must inevitably call. 



F. Str,\tton. 



