128 MR. F. McCLEAN ON THE COMPARATIVE PHOTOGRAPHIC 



The areas A, B, C, D, and AA are included in the present series of photographs. 

 Of these the first four constitute a complete hemisphere, symmetrically divided by 

 the galactic plane, and the deductions as to distribution have been made from them. 



The stellar spectra have been arranged in series, and classed separately for the 

 respective areas to which they belong. It appears at once that SECCHI'S Type I. 

 requires further subdivision into distinct classes. To effect this, a series of divisions 

 in parallel to SECCHI'S types have been adopted, in which Divisions I., II., and III. 

 correspond to Type I., and Divisions IV., V., and VI. to Types II., III., and IV. 

 respectively. 



The classified tables of the stellar spectra are given at the end of the paper, and 

 previous classifications by SECCHI in 1866-1868, by VOGEL in 1883, by PICKERING in 

 1890, and by LOCKYER in 1892 are indicated in separate columns. 



Division I. includes all stars whose spectra are characterised by the lines of 

 hydrogen and of cleveite gas. 



Subdivision I. (a) shows other special lines in addition. I have made a close com- 

 parison with the spectra of nearly all the elements, for the purpose of identifying 

 these extra lines, but without definite result. The only suggestion that presents 

 itself to me is the possibility of their being due to oxygen. 



I have placed below the scale attached to these spectra RUNGE and PASCHEN'S 

 spectrum of cleveite gas, which forms the characteristic spectrum of the division. 

 Also THALEN'S spark spectrum of oxygen. Although there is not a perfect agreement 

 between the spectrum of oxygen and the special lines referred to, there is a very 

 remarkable correspondence. 



I have further placed below the scale CAMPBELL'S bright-line spectrum of the 

 nebula in Orion. The general coincidence with the stellar line leaves little doubt as 

 to the close connexion between this class of stars and the gaseous nebulae. 



Evidence to the same effect is afforded by the wonderful photographs taken in 

 recent years, showing the physical connexion of many of these stars with the nebulae. 

 Such are Dr. EOBERTS'S photographs of the Pleiades and of the great nebula in 

 Orion. Alongside copies of these I have shown the corresponding groups of the 

 spectra of the involved stars ; the respective stars and their spectra are easily 

 identified on inspection. All six stars of the Pleiades show the cleveite gas 

 spectrum, but the presence of the special extra lines is doubtful. The Orion stars, 

 which include i and 6 Orionis, all show the cleveite spectrum, but in these the special 

 lines are also recognised. 



We have thus evidence of both physical and chemical connexion between these stars 

 and the nebulse. 



[Note added 8th April, 1897. There are two other instances of the connexion of 

 stars of Subdivision I. (a) with nebulse. 



BARNARD, in 1895, photographed an extended nebula in the vicinity of a Scorpii 

 (Antares). He mentions <r Scorpii as connected with the nebulosity. The photo- 



