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



a. Vapours produced at the lowest temperatures will be the first 

 to appear. 



/3. The spectrum of each substance must vary with the quantity of 

 vapour produced as the temperature increases, and the new 

 absorptions produced must be the same and must follow in the 

 same order as those observed in laboratory experiments. 



II. The carbon spectrum must first get more intense and then 

 diminish afterwards as the spaces, now smaller, are occupied by 

 vapours of other substances. 



ac. The longest spectrum will be that produced by mean spacing. 

 /3. The masking of the dark bands by the bright ones must vary, 

 and must be reduced as the mean spacing is reduced. 



III. The continuous spectrum of the meteorites must increase. 



a. There will be a gradually increasing dimming of the absorption 



bands from this cause. 

 /3. This dimming will be entirely independent of the width of the 



band. 



IV. The spectrum must gradually get richer in absorption bands. ^ 



a. Those produced at the lowest temperatures will be relatively 

 widest first. 



p. Those produced at the highest temperatures will be relatively 



widest last. 

 7. They must all finally thin. 



These necessary conditions, then, having to be fulfilled, I now 

 proceed to discuss M. Duner's individual observations. I shall show 

 subsequently that there are, in all probability, other bodies besides 

 those he has observed which really belong to this group. 



II. Discussion of Duner's Individual Observations. 

 Consideration of the Extreme Conditions of Spacing. 



Caiteris paribus, when the interspaces are largest we should have a 

 preponderance of the radiation of carbon, so far as quantity goes. The 

 bands will be wide and pale, the complete radiation will not yet be 

 developed ; a minimum of metallic absorption phenomena — that is, 

 only the flirtings of magnesium (8 and 7), the first fluting of manga- 

 nese (3), and the first fluting of iron (2) ; but the great width of the 

 bright band at 517 will mask band 8. 



When the interspaces are least, the radiation of carbon should give 

 place to the absorption phenomena due to the presence of those 

 metallic vapours produced at the highest temperature at which a 

 swarm can exist as such; the bright flutings of carbon should be 



