584 



NATURE 



[January 28, 191 5 



to describe individual occurrences, beginning; with 

 the most important of all, that of Sudbury, in 

 the northern portion of Ontario. Their descrip- 

 tion of the Sudbury mining; field is illustrated by 

 a g"eolog;ical map of the area and by a plan and 

 section of one of the important mines. A brief 

 history of mining- in the district is given, and the 

 account concludes with a table showing the total 

 production of the field and the average content 

 of nickel and copper in the ore smelted at Sud- 

 bury. Then follow briefer descriptions of similar 

 deposits in Norway, Sweden, and other countries. 

 A special feature of the work is the abundance 

 and excellence of the illustrations. Each section 

 is preceded by a bibliography, and the value of 

 the book as a work of reference is thus greatly 

 increased. Mr. Truscott has done his work so 

 well that in reading the book one is apt to forget 

 that it is a translation. 



THE SIDEREAL PROBLEM. 

 Stellar Movements and the Structure of the Uni- 

 verse. (Macmillan's Science Monographs.) By 

 Prof, A. S. Eddington. Pp. xii + 266. (London: 

 Macmillan and Co., Ltd., 1914.) Price 6s. net. 



THE history of astronomy is in some ways 

 exceptional among the sciences. It is the 

 most laborious of all, and from this fact arises a 

 certain apparent discontinuity. For years the 

 work goes on, and outwardly there is no very 

 conspicuous result beyond the piling up of records 

 the true value of which must often be far from 

 obvious at the time. Naturally, this part of the 

 burden falls largely on the professional astro- 

 nomer, though we do not forget men like Groom- 

 bridge, inspired by a faith not always easy to 

 analyse. Sometimes a line of work of evident 

 value, like the attempt to measure the radial 

 velocities of the stars, is prosecuted for years 

 without any positive result before a new way of 

 advance is opened by realising the correct prin- 

 ciples of an appropriate instrumental design. Then 

 the stream flows with astonishing rapidity, as the 

 reader of Dr. Campbell's recent work on "Stellar 

 Motions " may see. Even in the absence of a deci- 

 sive factor of this kind there come times when 

 different lines of inquiry are seen to converge, and 

 with their confluence new points of view and fresh 

 possibilities which affect the course of the science 

 are suddenly opened out. 



Such a time seems to have arrived about the 

 beginning of the twentieth century. A large 

 number of propj^r motions were known with in- 

 creasing accuracy, the distances of a few stars had 

 been fairly determined. Photometric studies were 

 well advanced, and some progress had been made 

 NO. 2361, VOL. 94] 



in the problem, apparently so simple but in reality 

 so difficult, of counting the stars. Some of the 

 cruder notions to be observed in Struve's "Etudes 

 d 'Astronomic Stellaire " had been generally dis- 

 carded. But the prospect of a synthetic treatment 

 of the sidereal problem seemed remote indeed. 

 Prof. Eddington 's review of the progress made in 

 the last few years, to which he has himself made 

 notable contributions, is exceedingly welcome. 

 Here the results are stated in the clearest possible 

 way, and the problems which have been solved or 

 which lie before us in the future are defined in 

 precise terms. It is a valuable work which will 

 enable those who have not followed the progress 

 made step by step to realise what has been accom- 

 plished, and from which those who have some 

 familiarity with the matters discussed will derive 

 much advantage by seeing the subject treated as a 

 whole. 



The scope of the book is in one respect rather 

 severely limited. It is in no sense an historical 

 account of the subject. The references to any 

 investigations made in the course of the last cen- 

 tury are merely incidental and exceedingly brief. 

 For this the author himself expresses regret in 

 the preface. To have traced the historic order by 

 which the present situation has been brought 

 about would have been beside the purpose of the 

 work, and might have expanded it unduly. But a 

 clear preliminary statement of what had already 

 been accomplished by the year 1900 in elucidating 

 the structure and tendencies of the stellar universe 

 would ha-\e been very valuable. It would have 

 made it possible to do a little more justice to the 

 work of astronomers like Kapteyn, Seeliger and 

 Kobold, and it would have furnished some 

 standard of comparison by which to appreciate the 

 present position. 



Of the twelve chapters into which the book is 

 divided the first two describe succinctly the data of 

 observation which constitute the resources for 

 attacking the problem and a general outline of the 

 universe as the author conceives it. A singularly 

 interesting chapter on the nearest stars follows, ii 

 which a most skilful use is made of the smal| 

 sample of information open to discussion. Thi 

 known examples of that simplest type of stellat 

 motion in which the stars are recognised as pos- 

 sessing a common, uniform movement are nexU 

 described. This conception originated '^^'^^Wl 

 Madler and Proctor, and, reinforced by a knowr 

 ledge of radial velocities, bids fair to give detailed 

 information, as opposied to merely statistical re- 

 sults, of the most illuminating kind. There is no 

 reason to think that what has been done in this 

 direction is more than a beginning. 



After a chapter on the solar motion a fuilj 



