4IO 



NATURE 



[March 2, 1905 



Maxwell and to adopt this definition at the outset, 

 lor it is from the value of the energy that the co- 

 efficient is always calculated. 



The methods of vector analysis are so useful in 

 electromagnetic theory and present so little difficulty 

 that the reader naturally expects to find them used in 

 a book which is intended_ to present a " thoroughly 

 modern introduction " to that theory. The author 

 makes a slight use of this analysis in his later 

 chapters, but in the case of vector products adopts 

 a hybrid notation. In the true vector analysis, as 

 used by Heaviside, if the vector product of the two 

 vectors A and B, which make an angle 9 with each 

 other, be the vector C, the result is denoted by 



c=Vab, 

 wliile the magnitude (C) of the product is given by 



C = AB sin e. 

 In the author's notation the relation between C, A 

 and B is expressed by 



C = vAB sin 9, 

 the letter v serving to indicate that c Is at right 

 angles to the plane of a and b. It is difficult to see 

 that this hybrid notation has any advantage over 

 Heaviside's. 



A few misprints have been noticed in a list sent 

 out by the author; only a few others have been 

 detected. 



The reader has probably already gathered from 

 this review that the treatise can hardly be described 

 as that " good text-book " for which the student 

 searches. Yet it is undoubtedly a useful book, and 

 with a little modification and revision would be one 

 of the best books of its class. The student who is 

 fortunate enough to have it at hand will often turn 

 to it with profit. G. F. C. Se,4rle. 



ASTRONOMICAL LECTURES AT CHICAGO. 

 Astronomical Discovery. By Herbert Hall Turner, 

 D.Sc, F.R.S., Savilian Professor of Astronomy in 

 the University of Oxford. Pp. xi + 225. With 

 plates. (London : Edward Arnold, 1904.) Price 

 los. 6d. net. 



^"'HE object of this book and the reason for its 

 appearance are e.xplained in a short preface. The 

 purpose is " to illustrate by the study of a few 

 examples, chosen almost at random, the variety in 

 character of astronomical discoveries." The words 

 " almost at random " seem a little out of place, for 

 we learn that the book comprises the matter that 

 was originally delivered in a series of lectures to the 

 University students of Chicago, at the hospitable 

 invitation of President Harper. The expression is 

 probably not to be taken too seriously. It is not 

 likely that a distinguished astronomer, enjoying what 

 may be regarded as a cathedral position, would be 

 careless in the preparation of his material. He 

 would be anxious to give his best, both for the credit 

 of English astronomy and for his own reputation. 

 There is ample internal evidence, not only that the 

 lectures were carefully prepared, but also of judicious 

 selection. 



NO. 1844, VOL. 71] 



The subjects chosen are about equally distributed 

 between those that are made at the telescope and 

 those that have resulted from the discussion of the 

 observations so made. This will be seen from a list 

 of the several chapters or lectures — (i) Uranus and 

 Eros, (2) discovery of Neptune, (3) Bradley's dis- 

 coveries of aberration and nutation, (4) accidental 

 discoveries, (5) the sun-spot period, and (6) the 

 variation of latitude. Some subjects which might 

 have been e.xpected to find a place, such as the dis- 

 coveries resulting from the application of the spectro- 

 scope, have been omitted, but the list is sufficiently 

 varied, and we gratefully acknowledge having received 

 a considerable amount of pleasure from reading the 

 well-known and familiar tales, treated, as they are, 

 with the brightness and acuteness characteristic of 

 the author. 



The choice of the discovery of Uranus permits a 

 well-deserved tribute to be paid to the memory of 

 the elder Herschel for the keenness, assiduity and 

 patience which mark the work of that astronomer ; 

 while the mention of Eros allows something to be 

 said of the problem of the sun's distance and of the 

 history of those times when the discovery of a small 

 planet added something to the reputation of the lucky 

 discoverer. The Savilian professor has some amus- 

 ing remarks on the subject of naming the host of 

 small planets that diligence has added to our cata- 

 logues. He quotes the case of Victoria as giving 

 rise to an outcry by foreign astronomers, who objected 

 to the name of a reigning sovereign being found in 

 the list. But the real struggle of the purists was, 

 we believe, over the christening of Fortuna, which 

 Airy happily settled in favour of the discoverer's 

 choice, by aptly quoting the well known lines of 

 Juvenal : — 



" Nullum nunien habes si sit prudentia 

 Sed nos te facimus fortuna deam, caeloque locamus. " 



The second chapter or lecture is probably the least 

 satisfactory in the book. The tale might have been 

 told without parading the old scandal of sixty years 

 ago to such wearisome length. Controversy seems 

 out of place in lectures of this character. Prof. Turner 

 in reopening the old sore has apparently two objects, 

 the one, the whitewashing of ."Mry, and the other, 

 the besmirching of Challis' reputation. Very hard 

 things are said of tlie latter to which we do not wish 

 to give further currency by repeating, but on the 

 subject of Challis' lectures we doubt whether the 

 words given in Airy's " Life " will bear the construc- 

 tion put upon them by Prof. Turner. Tliere is no 

 evidence to show, or at least the author has not 

 produced it, that Airy's opinion was different in 1844 

 from what it was in 1834, when he wrote to the Rev. 

 T. J. Hussey : " I am sure it could not be done (pre- 

 dict the place of the disturbing planet) till the nature 

 of the irregularity was well determined from several 

 successive revolutions " (of Uranus), p. 43. Airy, it 

 may be suggested, did not believe the problem soluble 

 until he received Le Verrier's memoir in 1S46. 



The account of Bradley's discoveries is excellent, 

 and the feature in it which will be especially valued 

 is the brief history given of the Rev. James Pound, 



