:70 



KNOWLEDGE. 



[December, 1903. 



for supposing,' " tliat the moon was once inhabited, and 

 that Jupitev will be inhabited in some remote future.' This 

 has always liccu myown opinion, and I think that his method 

 of treating this particular question is very forcible. Up 

 to the present time geologists have Ijeeu disposed to claim 

 a much longer duration for the maintenance of the present 

 solar radiation than astronomers have been inclined to 

 allow. Without endeavouring to adjust this difference 

 between the two sciences, the inference is but reasonable 

 and fair that no planet in the system differing very greatly 

 in size from our earth, and therefore differing greatly 

 from it in rate of cooling, could have passed through the 

 same geological and biological epochs. There- are two 

 small points in this chapter which are stated too positively ; 

 these are : " The small size and mass of Mars being such 

 that it cannot retain aqueous vapour ; and the fact that- 

 Venus rotates on its axis in the same time as it takes to 

 rv>volve round the sun." These two statements ought not 

 to have been made without some caution to the reader 

 that these " stated facts .... are by no means 

 demonstrated, because founded upon assumptions which 

 may be quite erroneous." 



The promptitude with which the book has been brought 

 out has had its drawbacks, for there are several indications 

 of undue haste. Some of these are misprints, as " W. W. 

 Turner," on page 142, for "H. H. Turner," and "Barnham" 

 for "Burnham" on page 123, and again in the index. 

 Some seem to be due to misapprehension of the authorities 

 -quoted, or more probably to carelessness in expression due 

 to hasty writing. Thus, for example, on pages 59 and 60, 

 our author says that to the naked eye no extensive region 

 of the heavens is very cons])icuously deficient or superior 

 in the number of the stars which it displays; on page 123, 

 that all the variable stars are to be found among the 

 spectroscopic binaries ; and on page 106, that " sunspots 

 are of such enormous size that, when present, they can 

 easily be seen with the naked eye." as if this were always 

 the case. More curious are his inconsistencies. On 

 pages 91-93 he gives a brief account of the determination 

 of the sun's movement through space. This is in one of 

 the first six chapters written specially "for the general 

 educated body of readers," .... who are not " fairlv 

 acquainted -with modern astronomical literature." He 

 states there that the motion of the sun is probably about 

 12i miles a second. Later on, in chapter VIII., he 

 devotes some pages to showing that Prof. Tiu-ner and 

 myself "made demonstrably baseless statements," when 

 we sim]>ly called attention to this very solar motion. On 

 page 143 he objects to my quoting Sir Eobert Ball on the 

 existence of dark stars, but on page 172 he quotes an exactly 

 parallel passage from Sir Eobert Ball to support himself 

 when he finds it convenient to assume that dark stars 

 are immensely numerous. On page 50 he quotes Sir John 

 Hersehel's description of the Milky Way " because he, of 

 all the astronomers of the last century, had studied it 

 most thoroughly." On page 162 he contemptuouslv jmts 

 on one side Sir John Hersehel's remark " that the greater 

 brightness of the southern Milky Way conveys strongly 

 the imjjression of greater proximity"; this on the ground 

 of a feature of the beautiful charts by the late Mr. Sidney 

 Waters. It escaped Dr. Wallace's notice that the feature 

 in question was a necessary result of the projection 

 emploved. Whilst it siu-ely was a great mistake to argue 

 as if the Milky Way shone in the same manner as an 

 illuminated surface (see page 162). These are but a few 

 of many similar oversights or inconsistencies. 



Still, with all its drawbacks, the book is a wonderful 

 one to have been produced in so short a time by a man 

 who has devoted his foiu-score years to a science which is 

 not the one which forms the major part of the book. 



With all its want of precision, it is full of interest and 

 charm, es])ecially when we come to the chapters dealing 

 with the biological side of the question. 



Upon that question as a whole —the question whether 

 life-bearing planets can exist in other solar systems than 

 our own — the answer of science is clear and distinct. It is 

 precisely the same which Prof. Newcomb recently gave 

 concerning the possible inhabitants of Mars : '• The reader 

 knows just as much of the subject as I do, and that is 

 nothing at all." Within our solar system we can indeed 

 form some crude estimate of probabilities ; Ijeyond it, 

 nothing. All the amazing progress of modern science, all 

 the revelations made by the spectroscope or by photography, 

 all the advance in biology, have not brought us one step 

 nearer an answer to the question, " Is this the only 

 inhabited world?" We stand essentially where Whewell 

 and Brewster did half a century ago; or we might, indeed, 

 say where Galileo and Capoauo were three hundred years 

 ago. W^e can, indeed, spin out the discussion at greater 

 length than our predecessors, and can introduce a far 

 larger number of more or less irrelevant facts, but of 

 serious ai'gument, either for or against, we are entirely 

 destitute. 



THE MARKINGS AND ROTATION PERIOD 

 OF SATURN. 



By W^. F. Denning, f.r.a.s. 



The conspicuous markings observed in the northern 

 hemisphere of Saturn during the present opposition have 

 greatly encouraged observation of, and interest in, a 

 beautiful object. The complaint has sometimes been 

 made that this j)lanet, though forming an unique picture, 

 attractive in the highest degree, yet lacks variety and the 

 evidence of similarly great and abundant changes which 

 render the study of Jupiter so entertaining. But the 

 aspect of Saturn during the past summer has led to a 

 modification of opinion on this point, and has proved that 

 "the ringed orb" is occasionally the scene of extensive 

 disturbances, and that the vapours surrounding him are 

 travelling in parallel currents, diffei'ing in their relative 

 velocities even more widely than those on the surface of 

 Jupiter. In future years it is fair to assume, therefore, 

 that Saturn will be more closely studied than hitherto. 

 Apparently he has been somewhat neglected in the past ; 

 his ring-system has usually occupied chief notice, and 

 perhaps diverted attention from more important pheno- 

 mena displayed on the ball. In viewing this planet the 

 observer's principal aim has been to obtain glimpses of the 

 crape ring, Encke's division in the outer ring, or certain 

 of the satellites, and thus the configuration in detail of the 

 globe has escaped critical survey. 



Astronomical records furnish comparatively few in- 

 stances of irregular markings on Saturn, and when 

 objects of this kind have been detected they do not appear 

 to have always been followed with the necessary per- 

 sistency. Sir W. Herschel was the first to discover 

 evidences of rotation, and to determine a value for it. He 

 narrowly watched certain inequalities in a quintuple belt, 

 visible in the planet's southern hemisphere in 1793, 

 December, and 1794, .January, and wrote in the Philo- 

 sophical Transactions for the latter year, "I can at 

 present announce the reality of the quick rotation by 

 means of 154 revolutions of the planet," and " We may- 

 conclude that the period is exact to ± 2 min., and we need 

 not hesitate to fix the rotation of Saturn upon its axis as 

 lOh. 16m. 0-44s." 



Schroeter, of LiUenthal, made many observations of this 

 planet more than a cmtury ago, and derived rotation 



