May 2, 1887.] 



KNO^ATLEDGE ♦ 



157 



telescopic work extant. To use an American expression, it 

 fills the bill, and it does not more than fill it. Other works 

 there are which contain either too much or too little — that 

 is, considered with reference to the wants of the astronomical 

 student. Here tliere is enough to occupy the attention of 

 the amateur a.stronomer, while there is not enough either to 

 deter him, by suggesting the idea that an immense number 

 of objects must be studied before he can be regarded as 

 having fairly entered on astronomical research, or to engage 

 him in the time-wasting work of studying multitudinous 

 objects of the same class with no special purpose in view. 

 We happen to know that quite a number of intending 

 students of a-stronom}' have been driven from the proposed 

 pursuit by the mere aspect of works in which multitudes of 

 insignificant lunar details, thousands of records of planetary 

 observations, and myriads of measurements of close double 

 stars are recorded as matters worth studying. JIany times 

 we have been told that astronomy cannot be worth studying 

 (outside ofKcial observatories for commercial astronomy) if 

 for proficiency it lequires its students to devote days, 

 mouths, and years to 



Collecting toys 

 And trities for choice matters, worth a sponge ; 

 Like children gathering pebbles on the shore. 



Now in Captain Noble's book just about as much atten- 

 tion is directed to each subject as it fairly deserves, and this 

 has been done in such a way as to attract instead of repelling 

 the student. A student who works through the series of 

 observations described or suggested here will have done 

 fully as much as is necessary to prepare him for serious 

 work if he is able or inclined to enter on it. On the other 

 hand, should he be content, as most men must be, to regard 

 astronomy merely as a department of scientific study, he 

 will not feel that he has given more attention to the subject 

 than it fully merits. He will have derived much pleasure 

 from the work of observation, his views will have been 

 enlai'ged, and a measurable addition will have been made to 

 the value of life. (We take it the chief value of scientific 

 research outside definite gains from nature, resides in the 

 answer which the study of truth gives to the vain yet 

 persistent question, " Is life worth living?") 



The introductory matter on the telescope is excellent, 

 though it might be usefully supplemented by certain 

 instructions which the beginner nearly always requiies 

 before he can get a telescope to work sjitisfactorily. In 

 particular, the telescopic study of the sun requires some 

 limits which Captain Noble has omitted to supply. His 

 suggestion that to diminish the risk of the dark glass crack- 

 ing, the apeiture of the telescope should be reduced from 

 three to two inches is sound enough so far as safety is 

 concerned ; but the plan involves a very serious diminution 

 of defining power. The chapter on the moon is admirable, 

 infinitely better calculated to attract students to the tele- 

 scopic study of our satellite than the big but dishearten- 

 ing treatises mentioned by our author. W^e are glad 

 to see by the way that he has put his foot down 

 very definitely in the matter of lunar nomenclature. 

 Four hundred names appear in the map and accompanying 

 ILst, and surelv four hundred are sufiicient. A study 

 of the moon in\ olving the examination of more and minuter 

 objects may he aptly compared in value to the enumeration 

 of individual hairs upon the tail of the conventional cow. 

 This we know would have seemed rank heresy to that dear 

 old lady Mr. Birt, and will be rejected scornfully by his 

 selenographical successors ; but we shall wait until their 

 elaborate work has added one single live fact to astronomical 

 knowledge before we admit that we have erred. 



We note only one point in the chapter on the moon 



which is open to question, and that does not belong to the 

 subject proper of Captain Noble's treatise. Ho mentions 

 as an inexplicable fact the notable darkening of the floor of 

 Plato towards and until shortly after the time of full moon. 

 We venture to deny that any such darkening takes place ; 

 and we are sure that if Captain Noble will follow our own 

 method of testing the matter, using a Dawe's eyepiece or 

 other device for getting rid of the effect of contiust, he will 

 be satisfied that his inexplicable fact is a very readily 

 explicable illusion. There is, however, a very simple proof 

 of this in lunar photographs. We possess a very fine series 

 of twelve photogi-aphs by Rutherfurd, showing the moon in 

 all her phases. A careful comparison of these shows un- 

 mistakably that the floor of Plato grows lighter, not darker, 

 as the sun's altitude above it incresises. 



The chapters on the planets are excellent. They are as 

 interesting as the corresponding chapters in the first edition 

 of Webb's " Celestial Objects : " before that work was over- 

 loaded with uninteresting details, and so deprived of much 

 of its effective value. We observe that Captain Noble gives 

 the rotation-period of Mars as 21h. 37m. 22"735s. We 

 doubt veiy much whether jNIr. Proctor ever attached any 

 real value to the second and third decimal digits. The only 

 thing proved about the rotation of Mars is that in which ^Ir. 

 Proctor and the late Professor Kaiser of Leyden iigreed — 

 after the correction of two clerical errors of Kaiser's. 

 Comparing the observations made by Hugbens and Hooke 

 with those made in the years 186-t to 1882, the rotation 

 period of Mars has been shown to be 21:h. 37m. 22'7s., 

 within certainly less than 0'05s. either way.* 



The treatment of double stars in the chapter on " Fixed 

 Stars and Nebul<E " is admirable. Fifty double stars or so, 

 including all the typical varieties, are described and pictured 

 — enough to interest and instruct, not enough to weary. 

 In fact, with so simple and attracti\e a way of presenting 

 the subject, as manj' more might have been introduced, and 

 no harm done. Yet we aieglad that Captain Noble resisted 

 the temptation ; for though the student might have gone on 

 unwearied, he has, as it is, been taught the useful Ics.son, 

 much needed in such matters— ne quid nimis. 



We do not care to note trifling con-itjenila or defects in a 

 work so excellent as a whole as this. We may mention, 

 however, that the method of drawing ellipses with pins and 

 a thread is not worthy of a place in Captain Noble's book. 

 With far less trouble than the student would have to take 

 in getting his pins rightly placed and the string of the right 

 length, a much better ellipse may be drawn. We speak 

 with some experience, having drawn many thousands of 

 ellipses. The construction for representing the gibbous 

 phase of Mars (see pp. 81, 82) is not quite correct: it is 

 better to give the true elliptical form to the terminator. 

 One other shght suggestion we would offer. It may seem 

 hypercritical, but we somewhat object to the description of 

 Mr. Ward's unusual keenness of sight as '•' almost super- 

 natural " and " quasi-miraculous." It is exceptional, pos- 

 sibly unique ; but the terms used by Captain Noble imply 

 that it is not merely marvellous in degree (as assuredly it is), 

 but in kind (which assuredly it is not). 



* Others have since pretended to correct this by combining later 

 observations with the mean of other estimates, including Kaiser's 

 two estimates before the clerical errors were detected. But this 

 last mistake is manifestly absurd; and though each succeeding 

 opposition of Mars must necessarily enable us to improve our esti- 

 mate of the planet's rotation period, half a century at least must 

 pass before any correction amounting to one-twentieth of a second 

 can be introduced in this way. The estimates of William Herschel, 

 Miidler, Stcchi, and Schmidt were less exact than Proctor's and 

 Kaiser's (which were practically identical), but they were inde- 

 pendent ; those prollertd by Messrs. Denning and Bakhuysen have 

 no independent value whatever. 



