1888.] 



of the various Species of Heavenly Bodies. 



17 



experiments may be repeated, with greater precision, by means of an 

 object-glass of greater dimensions."* 



He did not attempt to classify his observations on stellar spectra, 

 but, as pointed out by Professor Duner (" Sur les Etoiles a Spectres de 

 la Troisieme Classe," p. 3), those that he most particularly mentions 

 are really remarkably diverse in their characteristics. 



In these researches Fraunhofer was followed by Rutherfurd, who, 

 in the year 1863, was the first to indicate that the various stellar 

 spectra which he had then observed were susceptible of being 

 arranged into different groups. His paper was published in ' Silliman's 

 Journal' (vol. 35, p. 71), and, after giving an account of the observa- 

 tions actually made, continues as follows : — 



" The star spectra present such varieties that it is difficult to point 

 out any mode of classification. For the present, I divide them into 

 three groups : — First, those having many lines and bands, and mostly 

 resembling the sun, viz., Capella, Geminorum, a Orionis, Aldebaran, 

 7 Leonis, Arcturus, and /3 Pegasi. These are all reddish or golden 

 stars. The second group, of which Sirius is the type, presents spectra 

 wholly unlike that of the sun, and are white stars. The third group, 

 comprising a, Yirginis, Rigel, &c, are also white stars, but show no 

 lines ; perhaps they contain no mineral substance, or are incandescent 

 without flame." 



Soon afterwards Secchi carried on the inquiry, and began in 1865 

 by dividing the objects he had then observed into two types. These 

 two types were subsequently expanded in 1867 into three (' Catalogo 

 delle Stelle di cui si e determinato lo Spettro Luminoso,' Secchi, 

 Parigi, 1867) : first, white stars, like a Lyrae; secondly, yellow stars, 

 like Arcturus ; and thirdly, deeply coloured stars, like a. Herculis 

 and a. Orionis. The order of these types was not always as stated, 

 but I have not been able to find the exact date at which the order 

 was changed (Duner, "Sur les Etoiles," p. 128). Secchi subsequently 

 added a fourth type, in which the flutings were less numerous. 

 There is little doubt that Secchi was led to these types not so much 

 by any considerations relating to the chemical constitution of the 

 atmospheres of these bodies, as in relation to their colours. His first 

 plassifi cations, in fact, simply separated the white stars from the 

 coloured ones (see on this point 1 Le Scopirte Spettroscopiche,' A. 

 Secchi, Roma, 1865). 



The fourth type included, therefore, stars of a deeper red colour 

 than those of the third, and Secchi pointed out that this change of 

 colour was accompanied by a remarkable change in the spectrum ; in 

 fact, of Secchi's four types thus established, the first and second had 



* " On the Kefractive and Dispersive Power of Different Species of Glass, with an 

 Account of the Lines which cross the Spectrum." — Fraunhofer, translated in 1 Edin- 

 burgh Philosophical Journal,' vol. 10, October to April, 1823-24, p. 39. 



VOL XLIV. C 



