Dec. lo, 1 885 J 



NA TURE 



features — the change of latitude in the locale of the 

 spots — is altogether unnoticed. Chapter III., on the 

 IVIoon, contains a little sketch-map of the moon and de- 

 scriptions of the most striking formations. The laws of 

 eclipses, the use of the moon in navigation, and Nasmyth 

 and Carpenter's theory of the volcanic origin of the lunar 

 craters are treated of with the author's usual clearness 

 and at considerable length. In the concluding para- 

 graphs Dr. Ball expresses his belief that forms of life 

 unknown to us may probably e.'cist on many of the 

 celestial bodies, and applies to the question of the 

 plurality of worlds the lines of Tennyson : — 

 " This truth within thy mind rehearse, 

 That in a boundless universe 

 Is boundless better, boundless worse." 



The fourth chapter deals with the solar system as a 

 whole, with the detection and identification of planets, 

 with the positions and dimensions of their orbits and 

 their own comparative sizes. It is followed by a chapter 

 on the Law of Gravitation, a most important one, and 

 admirably written. The law of gravitation is so important 

 in itself, and so little understood by the unscientific por- 

 tion of the public, that such an explanation as is here 

 supplied is much needed. 



The succeeding chapters deal with the planets one by 

 one, beginning with Vulcan, the " Planet of Romance,'' 

 which Dr. Ball is inclined to believe was really seen by 

 Prof. Watson during the total solar eclipse of 1878, on 

 the not unreasonable ground that an observer of his 

 experience and skill was not likely to have been mistaken. 

 In the chapters on the other planets the points to which 

 most attention has been paid are the descriptions of the 

 various modes of determining the sun's distance, and 

 the size, form, and weight of the earth. There is a 

 pleasing and somewhat full biography of the elder 

 Herschel in the chapter on Uranus, and the wonderful 

 story of the discovery of Neptune is told again in a fresh 

 and engaging style. Leaving the regular members of the 

 solar system, we come to the comets and shooting-stars, 

 and with these Dr. Ball begins to treat his subject in a 

 somewhat more original manner, and there is very 

 much to commend in these and the following chapters. 

 Encke's comet, the evidence it affords as to a resisting 

 medium, and its usefulness as a means of determining 

 the masses of Jupiter and Mercury and the distance of 

 the Sun, occupy a considerable space. Bredichin's theory 

 of comet's tails is clearly explained. Dr. Ball is, how- 

 ever, scarcely correct in authoritatively classing the great 

 comet of 1843 H-S a non-periodic one, and the similarity of 

 its orbit to those of the great comets of 18S0 and 1882 

 surely deserved a word of notice. In the chapter on 

 shooting-stars he draws a sharp distinction between 

 meteors and meteorites, and expresses his conviction that 

 Prof Newton was wrong when he spoke of a meteoric 

 stone as having probably been part of a comet. He also 

 broaches and supports by some ingenious reasoning the 

 idea that meteorites are largely of terrestrial origin, and 

 he points out that meteorites of iron are much less frequent 

 than those of stone. 



Chapter XVIII. is on "The Starry Heavens," and is 

 especially commendable for the series of little diagrams 

 in which the relative positions of the principal fixed stars 

 are shown with admirable distinctness. Nothing can be 



easier than for the reader with this portion of the book 

 in hand to make himself acquainted with the general con- 

 figuration of the northern constellations. Several in- 

 structive points are well brought out in the two following 

 chapters, but in Chapter XXI., on the Distances of the 

 Stars, we find Dr. Ball on ground which he has largely 

 made his own. Herschel's attempt to form a conception 

 of the distribution of the stars in space is clearly ex- 

 plained, and made the basis of a detailed description of 

 the method of determining the distance of a star by its 

 annual parallax, and the cases of 61 Cygni, a Centauri, 

 and Groombridge 1S30 are dealt with at considerable 

 length. The difficulties of parallax work are sympathetic- 

 ally described, and the drawback often experienced of a 

 long series of observations failing to show any parallax 

 at all is made the occasion for enlarging on a particular 

 instance of such a failure, viz. Nova Cygni, 1876. The 

 chapter concludes with an explanation of Herschel's dis- 

 covery of the motion of the solar system towards the 

 constellation Hercules. The spectroscope is much more 

 sparingly dealt with, and the entire range of astronomical 

 spectroscopy is despatched in one of the shortest chapters 

 in the book. It is not possible that so condensed an 

 account should be very thorough or complete, but, given 

 the necessity to confine the subject within these limits, it is 

 difficult to see how it could have been much better done. 



The three following chapters deal with Star Clusters, 

 and Nebula;, Precession and Nutation, and the Aberration 

 of Light. Each of these subjects is well handled; the 

 explanations of the three kinds of apparent motion shown 

 by the stars being clearly and carefully explained, without 

 going into any details which would be likely to prove too 

 abstruse or tedious for any ordinary reader. The chapter 

 on Nebula; is illustrated by three plates, one of which, 

 Trouvelot's drawing of the Great Nebula in Andromeda, 

 is very well executed. 



The two concluding chapters are of especial interest. 

 Chapter XXVI., on " The Astronomical Significance of 

 He.it," deals with the most important points in the history 

 and method of the evolution of the solar system ; the 

 presence of heat in the body of the earth, the law of cool- 

 ing, the heat of the sun and its possible sources, the 

 doctrine of energy, the nebular theory and the evidence 

 which supports it. With respect to this last it should be 

 observed that the old illustration of the trees in the forest 

 is by no means very apposite. Dr. Ball is, however, 

 careful to distinguish such a theory, however magnificent 

 and attractive, from the truths of astronomy properly so 

 called. 



From nebular evolution we pass naturally to tidal 

 evolution. It is but comparatively recently that Dr. 

 Ball's lecture upon this subject was reported in these 

 pages, so that it is only necessary to say that the romantic 

 story is well told this second time. The criticisms to 

 which the theory was subjected are not referred to here, 

 though some deserved greater consideration than to be 

 silently passed over. 



As we have already said, this is in no sense whatsoever 

 a student's book. Dr. Ball has already shown how well 

 qualified he is to produce such a work when he desires to 

 do so, but he has had an entirely different purpose here. It 

 may be doubted whether he has not in some instances 

 been too general and undefined in his mode of treating 



