1888.] of the various Species of Heavenly Bodies. 29 



of the spectrum, in the red, or in other words the strengthening of 

 the spectrum in the green and blue, exactly where the carbon 

 bands lie. 



But in all the bodies of Group I which possess forms visible to us 

 in the telescope, it would seem proper that their classification should 

 depend mainly — at present at all events — upon their telescopic ap- 

 pearance, and there is very little doubt that a few years' labour with 

 the new point of view in the mind of observers armed with sufficient 

 optical power, will enable us to make a tremendous stride in this 

 direction ; but it seems already that this must not be done without 

 spectroscopic aid. For instance, if what I have previously suggested 

 as to the possible origin of the planetary nebulae be accepted, it is 

 clear that in those which give us the purest spectrum of lines — one in 

 which there is the minimum of continuous spectrum — we find the 

 starting point of the combined telescopic and spectroscopic classifica- 

 tion, and the line to be followed will be that in which, ceteris paribus, 

 we get proofs of more and more condensation and, therefore, more 

 and more collisions, and therefore higher and higher temperatures, 

 and therefore greater complexity in the spectrum until at length 

 " stars " are reached. 



When true stars are reached those in a cluster may appear nebulous 

 in the telescope in consequence of its distance ; the spectroscope must 

 give us indications of absorption. 



It is not necessary in this connexion, therefore, to refer to un- 

 doubted star clusters, as the presence of absorption will place them 

 in another group ; but the remark may be made that it is not likely 

 that future research will indicate that new groupings of stars, such 

 as Sir Wm. Herschel suggests in his paper on the breaking up of the 

 Milky Way, will differ in any essential particular from the successive 

 groupings of meteorites which are watched in the nebulae. Space 

 and gravitation being as they are, it is not necessary to assume 

 that any difference of kind need exist in the groupings formed by 

 stars and meteoric dust ; indeed there is much evidence to the con- 

 trary. 



II. Sub-Group. Bright-line Stars. 



It might appear at first sight that the distribution of bright- 

 line stars among various species should be very easy, since a constant 

 rise of temperature should bring out more and more lines, so that 

 species might be based upon complexity of spectrum merely. 



But this is not so, for the reason that the few observations already 

 recorded, although they point to the existence of carbon bands, do not 

 enable us to say exactly how far the masking process is valid. Hence 

 in the present communication I content myself by giving some details 

 relating to masking, and the results of the discussions, so far as they 



