December ii, 1919] 



NATURE 



n^ 



The first two lectures, on the solar system and 

 on comets, are by the director of the Lick 

 Observatory. Surely the time is at hand for an 

 advance in our knowledge of the physics of 

 comets. Dr. Aitken, who has acted as editor of 

 the volume, is responsible for three lectures — on 

 solar eclipses, on the moon, and on recent results 

 from stars and nebula. Dr. H. D. Curtis dis- 

 courses on nebulae and on some aspects of astro- 

 nomical discovery. Four single lectures are by 

 Dr. Crawford on epochs in astronomical history, 

 by Dr. St. John on the sun, by Dr. Leuschner on 

 motions in the solar system, dealing mainly with 

 recent computing work at Berkeley, and by Mr. 

 Scares on the brightness, colours, distribution, 

 and motions of the stars. These last three are 

 very useful summaries of current work. The final 

 lecture, on the Mount Wilson loo-in. reflector, 

 was delivered by 13r. Ritchey, but not reduced to 

 writing, and, owing to the lecturer's preoccupa- 

 tion with war work, it has been necessary to 

 substitute an account compiled from other sources. 



The book deserved an index. The photograph 

 of the Pleiades (plate xliv.) was not by Sir Isaac 

 Roberts. Did space not forbid, one would be 

 tempted to dispute some of Dr. Crawford's views 

 of history. Both he and Dr. Leuschner disparage 

 Kepler's achievements by calling them guesswork. 

 If to be fertile in hypotheses and to submit them 

 instantly to the test of comparison with good 

 observations be guesswork, then a good part of 

 the truest scientific method is guesswork. Of 

 this part Kepler is the supreme and unrivalled 

 example. 



(2) A reviewer would be quite justified in declin- 

 ing to take Mr. Black's little book seriously. It 

 is a dreary collection of petty calculations, made 

 with 7-figure logarithms when 4-figure would 

 have been ample and printed in extenso. As there 

 is no clear and intelligible summary, it takes no 

 little trouble to find out what is the precise object 

 aimed at, or how successfully that object is at- 

 tained. But the effect is to set up an empirical 

 relation between the rotation periods of the planets 

 and their masses and radii, which may be ex- 

 pressed by the formula (p. 56) 



T,_/R,U /£,\4_/M,\4 f^A' 



tf = M/R2 being the surface gravity; the corre- 

 sponding suffix notation is not Mr. Black's. Now 

 among the eight planets the rotation periods of 

 four are practically unknown. Obviously, three 

 assumed periods can be satisfied rigorously by a 

 proper choice of the two exponents. Hence a con- 

 -lent result for the liarth. Mars, and Jupiter, 

 vith a 20 per cent, error for .Saturn, has nothing 

 impressive about it. The author then goes on to 

 'implicate his formula further by introducing 

 imaginary satellites skimming over the surface of 

 imaginary planets, and the effect (p. 59) can be 

 I xprcssed in the form 



■\\-\nJ \\i.J \\)\K.->) \M^H./J ~\mJ \\<J ■ 



So the results are naturally the same. In fact, Mr. 

 NO. 2615, VOL. 104] 



Black plays on himself a variant of the old game 

 beginning "Think of a number" with a porten- 

 tous elaboration which may amuse some readers. 

 On p. 59 the Sun should be substituted for the 

 first planet mentioned in the definitions of both 

 M and m. 



The foundation of a second essay rests on the 

 approximate equality of the mass ratios 



Jupiter Saturn Uranus Neptune 

 Mart ~ Mercury' Venus ~ Earth 

 Of course, the mass of Mercury is really unknown, 

 but it is rather remarkable that Newcomb's 

 masses for Uranus and Neptune only require an 

 adjustment each within 2 per cent, to make the 

 second relation exact. With this slender material 

 the author again builds up elaborate arithmetical 

 combinations and finds an evident delight in 

 results which are nothing more than simple 

 numerical verifications of the laws of proportion. 



H. C. P. 



THE DOMINION OF MAN. 



The Outline of History : Being a Plain History of 

 Life and Mankind. ' By H. G. Wells. With the 

 editorial help of Mr. Ernest Barker, Sir H. H. 

 Johnston, Sir E. Ray Lankester, and Prof. 

 Gilbert Murray. To be completed in about 

 twenty fortnightly parts. Part i. Pp. 32. (Lon- 

 don : George Newnes, Ltd.) Price is. 2d. net. 



T N this first part of his " Outline of History " Mr. 

 ^ H. G. Wells has surpassed the old author who 

 carried the Trojan war back to Leda's eggs, for 

 he begins with our solar system as a nebula con- 

 densing into sun and planets, and our earth as a 

 mass of glowing matter. He tells how, in the 

 course of cooling, an ocean gathered on its 

 surface, on the margin of which the first struc- 

 tureless organic matter at last appeared, from 

 which, in the course of ages, the earth's living 

 tenants were developed. He describes in graphic 

 terms not a few characteristic members in their 

 succession, some of which are well depicted by 

 Mr. J. F. Horrabin. Once or twice a phrase occurs 

 "to which we may demur : for instance, the nautilus 

 is not a genus of ammonite ; volcanic eruptions 

 are more often a consequence than a cause of 

 mountain upheaval ; and we doubt whether the 

 changes between the Mesozoic and the Kainozoic 

 were so "catastrophic" as he implies. But these 

 are trifles, and we find, after a discussion of the 

 estimates of geological time, a good sketch of 

 natural selection and the changes of species. As 

 these changes in life depend not only on altera- 

 tions in the world's physical geography, but also 

 on its climate, the causes of the latter are briefly 

 explained. 



Next, Mr. Wells, after sketching the strange 

 living tenants of the earth in ages when no crea- 

 ture with a backbone existed in sea or on land, 

 brings before his readers the strange aspects of 

 the earlier vertebrates, such as Pareiosaurus, 

 which, low down as it is among the reptiles, 

 seems as if striving to be a mammal. This leads 



