4^- 



NATURE 



[August 29, 1S95 



THE SUN'S PLACE IN NATURES 

 X. 



The New Classification of the Stars. 



T NOW pais to the new classification of stars which has been 

 suggested by the totalitj- of the facts which I have so far 

 brought before you. 



Although the first obser\-ations of stellar spectra were made by 

 Fraunhofer, we owe to Rutherfurd the first attempt at clarifi- 

 cation. In December 1862 he wrote as follows :- 



" The star s)>ectra present such varieties that it is difficult to 

 point out any motle of classification. For the present I divide 

 them into three groups. First, th<ise ha\-ing many lines and 

 hands and most nearly resembling the Sun, viz. Capella, 

 R Geminorum, a Ononis, Aldcbaran, 7 Leonis, Arcturus, and 

 a Pegasi. These are all reddish or golden stars. The second 

 group, of which Sirius is the type, presents spectra wholly un- 

 like that of the Sun, and are white stars. The third group, 

 comprising a \'irginis, Rigel, &c., are also white stars, but 

 show no lines ; perhaps they contain no mineral substance, or 

 are incandescent without flame. 



" It is not my intention to hazard any conjecture based upon 

 the foregoing . pteervations ; this is more properly the province 



stars lie along one line of temperature, the highest temperature 

 being at one end, and the lowest at the other. Such, at all events, 

 is VogeKs view. Now we have to conclude that nebul.v are 

 stars to be, and that some apixirent stars are really nebula ; 

 and I think I h.ive shown ymi sufficient justification for the idea 

 that the undisturbed nebul.v are of relatively low temperature ; 

 hence we have boilies getting hotter as well as bodies getting 

 cooler, .and both must be provided for. 



In 1873 I^f- Vogel brought out a new and much more detaile<l 

 classification considerably extending the number of groupings 

 employed by Rutl-.erfurd and Secchi. This classification is bas«l 

 on the assumption that all stars began by t>eing ver)- hot, and 

 that the various changes observed in the spectra are due to> 

 cooling,' and the presence of bright lines is considered .as ai 1 

 matter of secondar)' importance only, and gives rise to suh 

 groupings only. 



Dr. Scheiner has quite recently accepted this statement. _ 

 appeals to his new observations of the s|ieclrum of magnesium as 

 a " direct proof of the correctness of the physical interpretation 

 of \"ogers spectral . classes, according to which Class II. is 

 developed by cooling from I., and III. by a further process of 

 cooling from II.'' (Astroiwiiiy and .-Islro-P/iysus, 1S94, p. 571.) 

 Pechiile was the first to object to Vogel's classification, mainly 



Group IT 



Group III f-^y 



iroup V 



Group II 



Group I 



Fig. 38. — Temperature cur\-c. 



^( -\ Group VI 



Groii). \1I 



of the chemist, and a great accumulation of accurate data should 

 be obtained Ii^-fore making the daring attempt to proclaim any of 

 the c : I -menls of the stars." 



Thi in was followed up by Secchi, who practically 



adopit.i iM. I.. nurd's three grou()s, changing, however, the word 

 group to tyfx;. and adding a fourth. On lhis|xjint Dr. (iould, 

 in his memoir ' of Rutherfurd, writes as follows : 



"I cannot forbear calling attention to the cl.assification, 



»^«entislly the same, .subsequently published by Secchi without 



■ this or to .any of the other laliours of Rutherfurd, 



is generally cited under Secchi's name." (See 



ir II.. r, ' p. 25S, and "Translation," pp. 235-236.) 



In these and other subsetjucnt cltissificalions— and of course 



wc must classify our stars if we are to sjieak about then with 



intelligence, and to understand the relations of one b.idy or 



<y«"m nf tKwlif, I0 nnnlher— it has been taken for granted that 



■ hatcver to do with stars, and that all the 



. .1'-.. of a countc of lectures to Workinn Men 

 lofjy (luring November and £>cccmber, ( 



> Kead before ihi 



NO. 13.1. 



vul. JIKIIV. p, 71, 



my, April 1B95. 



'"•• 52] 



on the ground that Secchi's ty|x.-s 3 and 4 had been improperly 

 brought together.'- Xow the views I have brought before you cut 

 at the root of such a cla.ssification ;is this. 



It is perhaps worth while in p;issing to point out that in the 

 course of lectures I gave here in 1S86 I stated, taking the then 

 classification as a basis ^ : — 



" On the nebular h)|>othesis, supmsing .... thai we 

 started with ordinary comelary materials, then, on the l)?- 

 ginning of a central condens.ation which in lime is to becomes 

 star, as Kant and Lapl?.ce suggested, such central condens^ilion 

 should then give us a star of the fiuirlh class. As the energy of 

 condensation increased and the temper.iture gol higher, the 

 .spectra would change llirough the third and second il.isscs, till 

 ultimately, 7v/i(ii llic Icmpcralurc -u-JS /lig/ust, the first i!;iss 

 spectrum would \k reache<l. On Ihe slnckcniiii; down oj Iht 

 tcmperaliirc of the now formed star, the spectra of the second, 

 third, and fourth classes would then be reproduced, but, of 

 course, now in the direct order." 



lil> " .Mctcuollc ilxx.tliot^, pp. 34^-0. 



» Ixickyer, Natlku, vol. xxxiv. 1BB6, p. mS. 



ill- l.s pre- 



lliiiicr. 



re i;ivci1 ill 



I 



