February 1, 1898.] 



KNOWLEDGE 



41 



curve, with ascending and descending branches. Miss 

 Maury's investigation goes further still. Her classification 

 lies not in one dimension but in two, and she finds it 

 necessary to divide the spectra she has examined, not only 

 into "groups," forming a nearly continuous series, from 

 spectra bearing a close resemblance to those of the bright- 

 line nebul.B, on to the long-period variables at the extreme 

 end of the series, but also into " divisions. " in which the 

 leading idea is not the substances producing the lines but 

 the character of the lines themselves. 



It is, of course, extremely unlikely that in this new 

 classification we have arrived at finality, any more than in 

 the classifications which preceded it. But this new factor 

 which Miss Maury has brought to light in the course of 

 her most patient study will certainly have to be reckoned 

 with in the future. 



The first division in Miss Maury's scheme — Division " — 

 is by far the largest, including three hundred and fifty- 

 five stars out of the total six hundred and eighty one. 

 In these spectra none of the single lines are relatively wide 

 except those of hydrogen and calcium, and all the lines 

 are " clear" — that is, they stand in distinct contrast to the 

 bright portions of the spectrum. Division '' comprises 

 stars in the spectra of which all the lines are relatively 

 wide and hazy. The fainter hnes therefore tend to 

 disappear, and in consequence those observed arc relatively 

 few ; but their relative intensity remains much the same as 

 in Division 'i, so that there does not appear to be a radical 

 difference of constitution between the two divisions. 



Division c is in general distinguished by the strongly 

 defined character of its lines, by the presence of certain 

 lines apparently not found in the solar spectrum, by a 

 difference in the relative intensities of the lines as com- 

 pared with the solar spectrum ; and, further, the lines of 

 hydrogen are narrow and well defined but less intense 

 than in the other divisions, whilst the calcium lines are 

 more intense. Stars of this division, therefore, would 

 seem to differ more in constitution from those of Division a 

 than do those of Division '■. 



Besides these three great divisions there are a large 

 number of intermediate forms, whilst quite one-sixth of 

 the total number of spectra cannot be assigned with 

 certainty to any of these divisions, either on account of 

 the faintness of the star or of the imperfection of the 

 photograph. 



The cross division into " groups " is less novel than the 

 one just noted into "divisions." Miss Maury's scheme 

 makes the " groups " twenty-four in number. Of these, 

 the first five are those in which the Orion lines are specially 

 prominent — a large number of the Orion lines being now, 

 of course, known to be those of helium. The sixth group 

 is intermediate between the Orion type and Secchi's first 

 type. The full members of this Secchi's first type are 

 divided into five groups according to the intensity of the 

 hydrogen lines, which are at their maximum in Group VII. 

 and decrease later, and to that of the solar and calcium 

 lines, which increase from group to group. The twelfth 

 gi-oup comprises spectra between the first and second types, 

 and the full members of Secchi's second type are divided 

 into four groups with respect to the increase of the solar and 

 calcium Lines. The third type is distributed over the next 

 four groups, bands and flutings replacing lines. As a neces- 

 sary consequence the divisional differences are no longer 

 noted ; indeed, no spectra of Division b are noted later than 

 Group Xn., or of l)ivision c later than (iroup XIV. The 

 twenty-first and twenty-second groups correspond to 

 Secchi's fourth type and Pickering's fifth type respectively. 

 There remain, then, two classes unnumbered : the " com- 

 posite " stars, which are probably doubles of difi'erent 



spectra apparently single from their extreme closeness, 

 and bright-line stars of the Orion type. 



The annexed little table, the eighth in Miss Maury's 

 Memoir, brings out in a singularly clear fashion the 

 continuity of the series into which she has thus arranged 

 the spectra in her hand. It will be observed that it is no 

 theoretic succession ; it is based upon the actual character 

 of the spectra as the photographs present them, and is 

 perfectly independent of any explanation which may be 

 offered as to the cause of the differences thus scheduled. 

 The succession may be one of temperature, of stage of 

 development, or of actual chemical constitution, and it 

 might be supposed to run in either direction without in the 

 slightest degree invahdating the classification here given. 

 On the subject of theory Miss Maury touches lightly, but 

 points out the close resemblance between Group I. and 

 that of Pickering's fifth type stars. Group XXII., and that 

 the latter connect us with the bright-line nebulw. This 

 consideration, taken in connection with the fact of the 

 obvious connection of the Orion type stars with the 

 nebular regions of Orion and the Pleiades, strongly supports 

 the view that the groups are numbered from I. to XX. in 

 their true evolutionary order. 



Group XXL, however, stands apart from this evolution. 



Table VUI. — Relative Ihikssities of Lines. 



Intensity 

 of 



Inteusity 



Intensity 



Inteusity 



Hydrogen. Orion Lines. | Solar Lines. 



For Miss Maury finds the difficulty of including the fourth 

 type stars in any regular progression which others have 

 found before her, and which Vogel and Lockyer have tried 

 to meet by such difi'erent expedients : the former placing 

 the third and fourth type stars as alternative forms for a 

 late stage in stellar life history, the latter regarding Type 

 III. as indicating an early stage in a star of rising 

 temperature, and Type IV. as a late stage in a star of 

 falling temperature. 



It is sufiiciently clear from these very difl'erent classifica- 

 tions that no very sure foundation for determining the 

 course of a star's evolution has yet been laid down : 

 but it seems to me that in placing the long-period 

 variables at the end of her series Miss Maury has been 

 guided by a true appreciation of the facts before her, and 

 that her scheme therein is a vital improvement on that of 

 Lockyer. And to leave the carbon stars, the fourth type, 

 unplaced, is probably, in the present state of our know- 

 ledge, to exercise a wise discretion, though Mr. McClean's 

 photographs of 1.52 Schjellerup appear to confirm Vogel's 

 suggestion that both Types III. and IV. succeed Type XL, 

 but as alternatives to each other. 



The connection between the divisions is a more difficult 

 matter, and except possibly in one point it has to stand 



