April 11, 1902.] 



SCIENCE. 



585 



represented in, the long chain of facts now at 

 our disposal touching the spectral changes 

 observed in the hottest stars.' 



The separate 'books' into which the small 

 volume is divided are entitled as follows : I., 

 'The Basis of the Inquiry'; II., 'Application 

 of the Inquiry to the Sun and Stars'; III., 

 'The Dissociation Hypothesis'; IV., 'Objec- 

 tions to the Dissociation Hypothesis'; V., 

 'Inorganic Evolution.' The work therefore 

 deals with a chemical problem by the methods 

 and with the results of astronomy. It does not 

 primarily treat of the theory of stellar evolu- 

 tion, which is now being gradually built up 

 on the foundation of the new facts of astron- 

 omy and astrophysics. The author presents his 

 evidence in his usual brilliant manner, and it 

 is easy to see how one may be carried along to 

 his conclusions, if the evidence is not carefully 

 examined. The dissociation hypothesis is un- 

 doubtedly a particularly alluring one to the 

 astronomer, as presenting a comparatively easy 

 escape from some of the difficulties of solar and 

 stellar physics. But the validity of the evi- 

 dence upon which any such theory is based 

 should be beyond question, and this cannot be 

 said of some of the evidence here presented. It 

 is also very doubtful if other workers in these 

 lines can share Sir Norman's optimistic view 

 expressed on page 29: "I propose to pass over 

 the history of nearly twenty years' work, with 

 all its attendant doubts and difficulties, and 

 deal with what that work has brought us, a 

 perfect harmony between laboratory, solar and 

 stellar phenomena." To many it may appear 

 that the discoveries of facts in spectroscopy 

 in recent years have tended to temporarily 

 diminish rather than increase the harmony 

 between the phenomena observed in the labo- 

 ratory and the heavens. 



The reviewer's copy of the book contains 

 many marginal queries as to the correctness of 

 the evidence brought forward as representing 

 the facts. Thus, for instance, we read on page 

 34 of "the simplification of the spectrum of a 

 substance at the temperature of the chromo- 

 sphere. To take an example, in the visible 

 region of the spectrum, iron is represented by 

 nearly a thousand Fraunhofer lines; in the 

 chromosphere it has only two representatives." 



Now recent photographs of eclipse spectra — 

 and first of these that obtained in 1896 by Sir 

 Norman's assistant, Mr. Shackleton — actually 

 show the presence of a great number of iron 

 lines at the base of the chromosphere, matching 

 almost every one of the strong dark lines 

 ascribed to iron in the solar spectrum. In sev- 

 eral places the assertion is made that the lower 

 chromosphere is certainly not the origin of the 

 Fraunliofer lines, although the author's own 

 photographs of the 'flash spectrum' at the 

 Indian eclipse of 1898 clearly contradict this. 

 We are surely much indebted to Sir Nor- 

 man for his valuable researches on the lines 

 having greater intensity in the spark than in 

 the arc spectrum, to which he has applied the 

 term 'enhanced lines.' But it is diificult to 

 avoid the impression that he attaches an 

 exaggerated importance to their significance in 

 solar and stellar spectra. To the vapors pro- 

 ducing the enhanced lines he prefixes 'proto,' 

 as proto-magnesium, proto-iron, suggesting 

 that at high spark temperatures a finer form of 

 the element is developed. The spectrum of a 

 Cygni is considered to contain chiefly the 

 enhanced lines; numerically, 120 enhanced 

 metallic lines were found in approximate coin- 

 cidence with some of the 307 lines measured in 

 the spectrum of a Cygni ; or, dealing only with 

 the strongest lines, 'the coincidences with 

 enhanced metallic lines with the dispersion 

 employed amount to 38' out of 40. The re- 

 viewer has not been able to fully confirm this 

 resemblance on comparing the wave-lengths 

 found in a Cygni by other observers with Sir 

 Norman's lists of enhanced lines of metallic 

 spectra, and had hoped to make the comparison 

 on recent plates taken at the Yerkes Observa- 

 tory ; but this would have too long deferred this 

 review. However, one of the points especially 

 emphasized by Sir Norman is the superior 

 temperature of the reversing layer of a Cygni 

 to that of the sun. As his reasoning is based 

 on the incorrect premise that the reversing 

 layer lies outside the chromosphere, the con- 

 elusions are not convincing. On this and simi- 

 lar evidence is constructed the author's elabo- 

 rate and ingenious classification of stars into 

 genera depending upon their density and tem- 

 perature, divided into ascending and descend- 



