34 



NA TURE 



[May 10, 1888 



ture such that fluting absorption mainly takes place, 

 although of course there must be some continuous ab- 

 sorption in the blue. This is perhaps the most highly- 

 developed normal spectrum-giving condition ; 44, 45, 55, 

 60, 65, 86, 92, 278 are examples. 



77ie Paling of the Flutings. 



Subsequently, the spectra are in all cases far from being 

 discontinuous, and the flutings, instead of being black, 

 are pale. Thus, while the bands are dark in the stars we 

 have named, they are not so dark in a Orionis. Here, 

 in short, we have a great distinction between this star 

 and a Herculis, o Ceti, R Lyrae, and p Persei. 



Obviously this arises from the fact that the average 

 distances between the meteorites have been reduced ; 

 their temperature being thereby increased as more col- 

 lisions are possible, the vapours are nearly as brilliant 

 as the meteorites, and radiation from the interspaces 

 cloaks the evidences of absorption. Nor is this all : 

 as the meteorites are nearer together, the area producing 

 the bright flutings of the carbon is relatively reduced, and 

 the bands 10 and 9 will fade for lack of contrast, while 8 

 and 7 will fade owing to the increased temperature of the 

 system generally carrying the magnesium absorption into 

 the line stage ; b is now predominant (see 102, 157, 163, 

 114,125,135). 



Under these conditions the outer absorbing metallic 

 atmosphere round each meteorite will in all probability 

 consist of Mn and Fe vapours, and in this position the 

 masking effect will least apply to them. This is so 

 (114, 116) ; they remain dark, while the others are pale. 



Here we have the indication of one of the penultimate 

 stages already referred to. 



Phenomena of Condensation. 



Dealing specially with the question of condensation, — 

 I have already referred to possibly the first condition of 

 all, recorded by Dundr in the observations now discussed 

 — I may say that the first real and obvious approach to it 

 perhaps is observed when all, or nearly all, except 9 and 

 10 of the flutings are wide and dark. The reasons will be 

 obvious from what has been previously stated. Still 

 more condensation will give all, or nearly all, the bands 

 wide and pale, while the final stage of condensation of 

 the swarm will be reached when all the bands fade and 

 give place to lines. We have then reached Class II. (107, 

 139, 168, 264) ; 2 and 3 should be and are perhaps the 

 last to go (203). 



The Bands 9 and 10. 



With regard specially to the bands 9 and 10, which 

 include between them a bright space which I contend is the 

 second fluting of carbon, I may add that if this view is 

 sound, the absence of 10 should mean a broad carbon 

 band, and this is the condition of non-condensation, 

 though not the initial condition. The red flutings should 

 therefore be well marked—whether broad or not does not 

 matter ; but they should be dark and not pale. Similarly 

 the absence of band 9 means non-condensation. 



Therefore 9 and 10 should vary together, and as a 

 matter of fact we find that their complete absence from 

 the spectrum, while the metallic absorption is strong, is a 

 very common condition (1, 2, 6, 16, 26, 32, 39, 40, 46, 

 54, 60). 



That this explanation is probably the true one is shown 

 by further consideration of what should happen to the 

 red flutings when 9 and 10 are present. As the strong 

 red flutings indicate condensation, according to my view 

 this condensation (see ante) should pale the other 

 flutings. This happens (3, 8, 13, 28, 35, 45, 30 ; and last, 

 not least, among the examples, I give 50, a Orionis). 



III. Results of the Discussion. 



The Line of Evolution. 



I have gone over all the individual observations 

 recorded by Duner, and, dealing with them all to the 

 best of my ability in the light afforded by the alloca- 

 tion of the bands to the various chemical substances, 

 the history of the swarms he has observed seems to be 

 as follows : — 



(1) The swarm has arrived at the stage at which, owing 

 to the gradual nearing of the meteorites, the hydrogen 

 lines, which appeared at first in consequence of the great 

 tenuity of the gases in the interspaces, give way to carbon. 

 At first the fluting at 473 appears (as in many bright-line 

 stars), and afterwards the one at 517. This is very 

 nearly, but, as I shall show subsequently, not quite, the real 

 beginning of Class 1 1 1. a, and the radiation is now accom- 

 panied by the fluting absorption of Mg, Fe, and Mn — 

 bands 7, 2, 3. This is the absorption produced at the 

 temperature of the oxy-coal gas flame, while the stars 

 above referred to give us the bright line of Mn seen at 

 the temperature of the bun sen. 



(2) The bright band of carbon at 517 narrows and un- 

 veils the Mg absorption at band 8. We have 8 now as 

 well as 7 (both representing Mg), added to the bands 2 

 and 3, representing Fe and Mn, and these latter now 

 intensify. 



(3) The spacing gets smaller ; the carbon, though re- 

 duced in relative quantity, gets more intense. The second 

 band at 473 in the blue gets brighter as well as 

 the one at 517. We have now bands 9 and 10 

 added. This reduced spacing increases the number of 

 collisions, so that Pb and Ba are added to Mg, Fe, and 

 Mn. We have the bands 2, 3, 4, 5, 6, 7, 8, 9, and 10. 

 This is the condition which gives, so to speak, the normal 

 spectrum 



(4) This increased action will give us a bright atmo- 

 sphere round each meteorite, only the light of the 

 meteorite in the line of sight will be absorbed : we shall 

 now have much continuous spectrum from the interspaces 

 as well as the vapour of carbon. The absorption flutings 

 will pale, and the Mg flutings will disappear on account 

 of the higher temperature, while new ones will make their 

 appearance. 



(5) Greater nearness still will be followed by the 

 further dimming of the bright carbon flutings including 

 the one at 517. The blue end of the spectrum will 

 shorten as the bands fade, narrow, and increase in 

 number. If the star be bright, it will now put on the 

 appearance of a Orionis ; if dim, only the flutings of 

 Fe and Mn(i), bands 2 and 3, will remain prominent. 



(6) All the flutings and bands gradually thin, fade, and 

 disappear. A star of the third group is the result. 



In the latter higher-temperature stages we must 

 expect hydrogen to be present, but it need not necessarily 

 be visible, as the bright lines from the interspaces may 

 cancel or mask the absorption in the line of sight of the 

 light of the meteorites ; but in case of any violent action, 

 such as that produced by another swarm moving with 

 great velocity, we must expect to see them bright, and 

 they are shown bright in a magnificent photograph of 

 o Ceti, taken for the Draper Memorial, which I owe to 

 the kindness of Prof. Pickering. I shall return to this 

 question. 



Stages antecedent to those recorded by Duner. 



So far I have referred to the swarms observed by 

 DuneV. The result of the discussion has been to show 

 that all the phenomena are included in the hypothesis 

 that the final stages we have considered are antecedent 

 to the formation of stars of Group III., bodies which give 

 an almost exclusively line absorption, though these bodies 

 are probably not yet stars, if we use the term star to 



