NA TURE 



505 



THURSDAY, MARCH 29, 1906. 



STARS AND NEBULA. 



The System of the Stars. By Agnes M. Clerke. 

 Second edition. Pp. xvi + 403. (London: A. and 

 C. Black, 1905.) Price 20s. net. 



THERE is much excellent sense in the French 

 proverb, " Prends le premier conseil d'une 

 femme, et non le second," which expresses the view- 

 that the intuitive instinct of a woman is a safer 

 guide to follow than her reasoning faculties; and 

 although in these days it is considered ungracious to 

 make this suggestion, evidence of its truth is not 

 difficult to discover in most literary products of the 

 feminine mind. It is no disparagement to Miss 

 Clerke to say that even she shares this characteristic 

 of her sex, so that sometimes she lets her sympathies 

 limit her range of vision in the field of stellar re- 

 search. No doubt this disposition is exercised un- 

 consciously, but what is an attractive instinct when 

 applied to ordinary affairs of life is derogatory when 

 it influences the historiographic consideration of con- 

 tributions to natural knowledge. 



There are many students of science who follow the 

 trend of a writer like Miss Clerke with lamb-like 

 sequacity, and consider it almost a presumption to 

 express any dissatisfaction with her presentment or 

 interpretation of scientific fact. It is a sign of weak- 

 ness to occupv a position of this kind; and particu 

 larly so when the author whose views are accepted 

 is not actively engaged in the investigation of the 

 field surveyed. Science is not a persuasion in which 

 personal opinion has to be respected whatever the 

 value of the material evidence in its support. We 

 may admire Miss Clerke's literary skill and be im- 

 pressed by the brilliant periods in which she frequently 

 encloses simple matters of fact, but, at the same 

 time, we may be permitted to recollect that she is a 

 bibliographer rather than an observer, and therefore 

 her works, be they never so distinguished as litera- 

 ture, need only be regarded as narratives by a spec- 

 tator, when the weights of the results and conclusions 

 recorded in them are being decided. There is, as 

 Francis Bacon knew, a vast difference between 

 opinions based upon the study of books and papers 

 and those derived from individual observation and 

 experience. " Studies themselves doe give forth 

 Directions too much at Large, except they be bounded 

 in by experience. Crafty Men Contemme Studies; 

 Simple Men admire them; And Wise Men Use them. 

 For they teach not their own Use ; But that is a 

 Wisdome without them and above them, won by 

 Observation. " 



This statement of Miss Clerke's position is neces- 

 sary by way of excuse for the temerity of a reviewer 

 who ventures to criticise some points in a work of 

 such a substantial character as the present one. The 

 book has been revised so completely that scarcely a 

 page of it remains the same as in the original edition 

 published fifteen years ago. In this period much new 

 work has been accomplished, and from it Miss Clerke 

 has selected what she considers to mark essential 

 NO. 1900, VOL. 73 J 



steps in the progress of sidereal science, to incorporate 

 with the results previously described. The task of 

 sidereal astronomy was formerly stated to be the in- 

 vestigation of " the nature, origin and relationships of 

 sixty million stars and upwards of eight thousand' 

 nebula;," but the numbers are now " 30,000,000 stars 

 and 120,000 nebulae." The discovery of terrestrial 

 helium has led to the recognition of a new stellar 

 type having helium rays prominent in their spectra, 

 while oxygen, silicon, and titanium are among other 

 substances the rays of which have been identified in 

 celestial bodies in recent years. Numerous stars have 

 been proved by the spectroscope to be close couples ; 

 and " Prof. Campbell showed in 1902 that, among the 

 entire multitude of stars, one in six or seven is so 

 constituted." From spectroscopic observations, it has 

 also been possible to determine that the solar system is 

 moving toward an apex in right ascension 277 30' 

 and declination +20 at the rate of 125 miles a second, 

 the probable error of the result being less than one 

 mile a second. The demonstration of the motion of 

 nebula? in the line of sight has shown that then- is 

 no difference in this respect between nebula; and stars, 

 and has thus removed a difficulty formerly offered to 

 the view that stars arise from a condensation of 

 nebulous matter. Finally, the large number of vari- 

 able stars found in certain globular clusters, the 

 phenomena presented by such temporary stars as Nova 

 Auriga; and Nova Persei, and the structure and dis- 

 tribution of nebulae in relation to the Milky Way, can 

 only be simply and sufficiently explained by the exist- 

 ence in space of clouds of obscure particles alone or 

 associated with luminous matter. The most note- 

 worthy discoveries of astronomical science in recent 

 years are, indeed, those which demonstrate or suggest 

 that space may include as much dark material as 

 bright. 



Until a few years ago it was believed that nebulae 

 are masses of glowing gas at a high temperature; 

 but Miss Clerke is now able to write, " experience 

 is wholly contradictory of the notion that nebula; are 

 excessively hot bodies." It is scarcely too much to 

 say that the evidence brought forward by Sir Norman 

 Lockyer in connection with his meteoritic hypothesis 

 of celestial evolution is chiefly responsible for the 

 change of view that has taken place. An astronomer 

 unfamiliar with the literature of astrophysics would 

 not, however, derive this impression from the study 

 of any parts of this book in which nebulas are dealt 

 with. Again, it is stated that a consensus of opinion 

 regards gaseous nebulae as being " luminous through 

 electrical excitement"; but though this is frequently 

 mentioned, there is no record of the suggestion made 

 in 1888, as the result of spectroscopic examinations 

 of meteorites, that in the Orion nebula " the hydrogen 

 is electrically excited"; yet this observation was re- 

 corded in the original edition of Miss Clerke's book. 



The low temperature of nebulae, electrical excitation 

 as a cause of luminosity, and the suggestion that the- 

 apparently continuous spectrum of white nebulae, like 

 the nebula of Andromeda, would prove to be an inter- 

 rupted band of colour, are all functions of the- 

 meteoritic hypothesis. These three points have been, 



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