Feb. 17, 1882.] 



KNOWLEDGE 



337 



accuracy the present views of astronomers in relation to 

 the subject matter. This remark is not intended to include 

 expressions of opinion on the one hand, or, on the other, 

 such statements as are subsidiary to explanations or illus- 

 trations, but only deHnite statements respecting astrono- 

 mical matters. With regard to all, or very nearly all of 

 these, the reader may trust our author with perfect con- 

 fidence. In this sense the work deserves the high praise 

 accorded to it, of being thoroughly trustworthy. 



Tlie arrangement of the work throughout is admirable, 

 and the treatment of individual subjects is at once lucid 

 and attractive. Here and there the style is rather common- 

 place, but it is never confused. Every sentence has one 

 meaning and one only. Moreover, the meaning of every 

 sentence lies on the surface. In these respects, too, many 

 who write on scientific subjects have failed to consider the 

 requirements of the general reader. To the mental etibrt 

 which the study of such subjects requires, they add the 

 effort required to determine the meaning of ambiguous 

 phrases. Moreover, Professor Newcomb commonly avoids 

 the mistake of using technical terms where ordinary terms 

 would serve equally well. 



The treatment of the subject is simple in another sense, 

 perhaps not quite so satisfactory. Professor Newcomb 

 leaves many matters unexplained which are commonly 

 explained with more or less fulness in treatises on general 

 astronomy. For instance, in nearly all such treatises we 

 find some explanation of those disturbances of Uranus by 

 Neptune which led to the discovery of the latter planet. 

 The explanation is usually incorrect, but that is a detail. 

 It always requires more or less mental effort either to follow 

 the explanation, or to discover that the e.xplanation is, as 

 usual, all wrong. No such effort is required in reading what 

 ProfessorNewcombsays respecting thediscoveryof Neptune, 

 simply because he contents himself with a mere statement 

 of facts. Possibly this was the wisest course in the case of 

 a treatise intended for general reading. It may be doubted 

 whether the true e.xplanation given by Sir J. Herschel, for 

 instance, has been followed by a tenth of his readers, or 

 whether one-tenth of the readers of Lardner's, Chambers's, 

 and other such works, detect the error underlying incorrect 

 explanations of this subject It is necessary, however, to 

 remind the reader of the work before us that the ease with 

 with which he follows the author here and elsewhere is 

 due to the circumstance that difficulties are avoided — they 

 are not overcome. This is even the case with Professor 

 Newcomb's treatment of the subject of the sun's distance, 

 which few have mastered more thoroughly than he has. 

 His statements respecting the various methods available 

 for determining the distance of the sun are thoroughly 

 trustworthy, and his opinion respecting the result to which 

 observations point may be accepted as the one which 

 accords best with the evidence. But the matter is not 

 explained. We are able, indeed, without making too long 

 an extract, to quote all that he says in the way of explana- 

 tion, which is simply this : — 



" In consequence of the parallax of Venus, two observers 

 at distant points of the earth's surface, watching her course 

 over the solar disc, will see her describe a slightly different 

 path, as shown in Fig. 50. It is by the distance between 

 these paths that tlie parallax has hitherto been deter- 

 mined." 



The general nature of parallax has been already ex- 

 plained, and the distinction between Halley's and Delisle's 

 methods for determining this distance is briefly indicated 

 further on. But the principle underlying both those 

 methods, as well as the photographic and heliometric 

 methods, is explained no further than in the sentence quoted 



above. It is not too much to say that it is not explained 

 at alL 



An important and, in our opinion, a valuable feature of 

 this work is the discussion of ideas more or less speculative 

 with regard to the heavenly bodies. There are some 

 astronomers who object strongly to the introduction of 

 ideas of this sort into treatises on astronomy. But the 

 objection seems unwise, not to say peevish. The chief 

 charm of the study of astronomy lies in reality in the 

 mystery which enshrouds the orbs of space. What we 

 know respecting these bodies is little ; the unknown is 

 infinite. Now, uncjuestionably, mere idle speculations, 

 not even suggested by observation, are profitless. But 

 speculations based on the results of observation and phy- 

 sical research are not only interesting, but fruitful. In 

 such speculations have originat<;d nearly all the hypo 

 theses from among which the established theories of 

 the science have been evolved. It is noteworthy that 

 the greatest astronomers have indulged freely in specula- 

 tions I'especting the unknown. Copernicus, Galileo, Kepler, 

 Newton, the Herschels, and a host of those to whom as- 

 tronomy owes the noblest of its ti-iumphs, have discussed 

 speculations and hypotheses, of which some have been for- 

 gotten, others are remembered only because of the theories 

 which they suggested, while some few have become them- 

 selves the theories of the science. It may, indeed, be truly 

 said that no astronomer who has been unwilling to allow 

 his thoughts to pass beyond the boundaries of the known 

 has ever made great discoveries. We are glad to see 

 that Professor Newcomb, while he has shown himself 

 an exact and careful observer, and while, in certain 

 departments of mathematical re.search, he has held 

 his own with the greatest mathematicians of our time, 

 is i-eady to consider subjects which belong as yet to 

 the region of speculation. He presents, for example, 

 the various theories respecting the sun's condition which 

 have been advanced by Secchi, Faye, Langley, and Young, 

 though three of these are certainly, and all four possibly, 

 erroneous. He adopts, with apparent approval, several 

 opinions respecting the condition of the larger planets whicli 

 have been advocated in recent years in this country. Ho 

 accepts the conclusions of the Bonds, Peirce, and Clerk 

 Maxwell respecting the condition of Saturn's rings. And 

 speaking generally, he presents astronomy, not as a subject 

 respecting which certain facts and statements have to be 

 committed to memory, but as a living science, full of 

 promise, though also full of mystery, presenting a grand 

 array of achievements in the past, but offering also a ^ast 

 number of noble problems for attack, and possibly for 

 solution, in the future. 



The present woik, it will be inferred, is a very valuable 

 contribution to astronomical literature. It is especially 

 characterised by originality of tone and treatment through- 

 out It is remarkable also for the care with which details 

 have been attended to, quotations verified, tables corrected, 

 and so forth — matters respecting which scientific writers 

 of eminence are not always so careful as they might be. 

 {To he continued.) 



TNTEl.r.iGEN'CE IX AxiMils. — J. H. sonds the following: — "An 

 amusinp; account of a pet baboon, in a letter from a friend at Zan- 

 zibar is communicated to Nature this week by Miss Julia VVedg-nood. 

 An interestin}^ statement (in relation to the contention that laughter 

 is one of the distinguishing attributes of man) is, that ' Judy,' the 

 baboon in question, nsed, when she romped with her mistress, ' to 

 open her mouth, show all her white teeth, and regularly laugh like 

 a child, especially when she was tickled.' She never laughed at a 

 joke, and nothing made her so savage as being langhod at." — 

 [Darwin gives similar instances in his work on the " Expression of 

 the Emotions."— Ed.] 



