26 



Mr. J. N. Lockyer. On the Classification [Apr. 12, 



The passage from the second group to the third brings us to those 

 bodies which are increasing their temperature, in which radiation and 

 fluting absorption have given place to line absorption. 



At present, the observations already accumulated have not been 

 discussed in such a way as to enable us to state very definitely the 

 exact retreat of the absorption — by which I mean the exact order in 

 which the absorption lines fade out from the first members to the last 

 in the group. We know generally that the earlier bodies will contain 

 the line absorption of those substances of which we get a paramount 

 fluting absorption in the prior group. We also know generally 

 that the absorption of hydrogen will increase while the other 

 diminishes. 



The next group — the fourth, brings us to the stage of highest 

 temperature, to stars like a. Lyrse ; and the division between this 

 group and the prior one must be more or less arbitrary, and cannot at 

 present be defined. One thing, however, is quite clear, that no 

 celestial body without all the ultra-violet lines of hydrogen discovered 

 by Dr. Huggins can claim to belong to it. 



We have now arrived at the culminating poiut of temperature, and 

 now pass to the descending arm of the curve. The fifth group, there- 

 fore, will contain those bodies in which the hydrogen lines begin to 

 decrease in intensity, and other absorptions to take place in conse- 

 quence of reduction of temperature. 



One of the most interesting problems of the future will be to watch 

 what happens in bodies along the descending scale, as compared with 

 what happens to the bodies in Group III, on the ascending one. But 

 it seems fair to assume that physical and chemical combinations will 

 now have an opportunity of taking place, thereby changing the con- 

 stituents of the atmosphere ; that at first with every decrease of tem- 

 perature an increase in the absorption lines may be expected, but it 

 will be unlikely that the coolest bodies in this group will resemble the 

 first one in Group III. 



The next group, the sixth, is Secchi's type IV, and Vogel's Class III6, 

 its distinct characteristics being the absorption flutings of carbon. 

 The species of which it will ultimately be composed are already appa- 

 rently shadowed forth in the map which accompanies Duner's volume, 

 and they will evidently be subsequently differentiated by the gradual 

 addition of other absorptions to that of carbon, while at the same 

 time the absorption of carbon gets less and less distinct. 



To sum up, then, the classification I propose consists of the follow- 

 ing groups : — 



Group I. — Radiation lines and flutings predominant. Absorption 



beginning in the last species. 

 Group II. — Mixed radiation and absorption predominant. 

 Group III. — Line absorption predominant, with increasing tern- 



