1888.] of the various Species of Heavenly Bodies. 55 



4. Ba band 514* 



i 



I ( 



LinesJ 5 -'' 



1 a 



1st, 2nd, and 3rd Ba flutings J 634 



L649 



Band 1, which extends from wave-length 649'5 to 663'8, has not 

 yet been allocated. 



Tests at our Disposal. 



In order to prove that my explanation of the nature of these 

 celestial bodies is sufficient, a discussion of the individual observa- 

 tions of them, seeing that differences in the spectra are known to 

 exist, should show that all the differences can be accounted for in the 

 main by differences in the amount of interspace ; that is to say, by a 

 difference between the relative areas of space and meteorite in a 

 section of the swarm at right angles to the line of sight. I say in the 

 main, because subsequent inquiry may indicate that we should expect 

 to find minor differences brought about by the beginnings of conden- 

 sation in large as opposed to small swarms, and also by the actual or 

 apparent magnitudes of the swarms varying their brilliancy, thus 

 enabling a more minute study to be made of the same stage of heat 

 in one swarm than in another. 



How minor differences may arise will be at once seen when we con- 

 sider the conditions of observation. 



The apparent point of light generally seen is on my view produced 

 not by a mass of vapour of more or less regular outline and structure, 

 but by a swarm of meteorites perhaps with more than one point of 

 condensation. 



An equal amount of light received from the body may be produced 

 by any stage, or number of nuclei, of condensation ; and with any 

 differences of area between the more luminous centre and the outliers 

 of the swarm. 



All these conditions producing light of very different qualities are 

 integrated in the image on the slit of the spectroscope. 



I have said " generally seen," because it has been long known that 

 many of the objects I am now discussing are variable, as well as red, 

 and that at the minimum they are not always seen as sharp points of 

 lightf but have been described as hazy. 



The severe nature of the tests at our disposal will be recognised 

 when we inquire what must follow from the variation of the spacing. 

 Thus, as the spacing is reduced — 



I. The temperature must increase. 



* In the early stages this band is masked by the vivid light coming from the 

 carbon in the interspaces. 



f Hind first noticed this in 1851. Quoted by Arago, ' Astronomie Populaire.' 



