576 



Stoney — Cause of Double Lines in Spectra. 



with the intensities 



2J^ cos* ^, intensity of (9 a) 

 • -(10) 



W sin^ ^, 



4a^sin-jr cos'^j;, 



(12) 



of which (when a is small) the first is strong, the third faint, and the second 

 excessively faint. 



Hence when one of the elliptic partials of the dominant motion of P is affected 

 by both apsidal motion and precession, we shall have an appearance in the spectrum 

 which may be represented diagrammatically by the following figures : where (a) 

 in each figure represents the spectrum of the original elliptic partial if undisturbed, 

 {b) what it becomes when there is apsidal motion, and (c) what it becomes when 

 there are both apsidal motion and precession. 



All the figures are drawn to represent the state of affairs which is probably 

 what prevails in the monad elements, viz. apsidal and processional motions, which 

 are slow in comparison with the revolution of P in the elliptic partials of its 

 dominant motion. In this case n and k are small in comparison with m. The 

 three motions may be in the same direction, or one of them in the opposite 

 direction to the other two. Hence arise four varieties. 



Variety 1. — The elliptic, apsidal, and processional motions in the same 

 direction. Here m, n, and k are all positive, and the resulting spectrum may 

 be represented diagrammatically by fig. 7 (c), and consists of a pair of lines with 

 satellites inside, the more refrangible group being the brighter. 



Variety 2. — The processional motion in the opposite direction to the other 

 two : in and n are positive, and k negative. 



737. 



(^) 



(i) 



(c) 



+ + + 



+ I 



i I I 



+ I 



+ ++ 



I + 



I I I 



I 



+ 



Fig. 7. 



Fig. 8. 



Fig. 8 (c) represents the spectrum : a pair, of which the more refrangible is 

 the brighter, with satellites outside. 



