( 442 ) 



or 



(-) 



Let ;.,. be the wavelengtii of tlie outer oomj)oiient of the (ri|>let 

 towards the red then, if P,, ?/ ïind .tv liave a sij^iiifieaiice cori'e- 

 spoiidiiig U) I hat of J\, f„ and ./■„, 



Xr' 



We have however ;.„ (P, -\- f,) = ?.r{Pr + f,), whence 



In like manner, X,-, P,^ 'V detei'niinin.ii- the coniitonenl of Ihe 

 lri|)let lowai'ds tlie violet, we have 



.,. = ;.'• f i,--"'-^^'0 



" 7', V 8 8 y 



In the case of radiation in a niagiielic held this expression may 

 often still be siini)lilied. In many eases we may choose 



F, = rr=Pr (4) 



Looking at the system of rings corresponding \o /„, while the 

 magnetic force is slowly but gradually increased one sees at the 

 same time rings which proceed from the system ;.„ and are moving 

 outwards and others which are mo\ing inwards. The rings corre- 

 sponding to /, are conlracliug, those corresponding to P.,. are ex- 

 pan<ling. 



It depends upon the value of /; of the étalon and upon the 

 inlensitv of Ihe magnetic Held how great the expansion and contrac- 

 tion of the rings, in comparison with the distance of the rings P.^, 

 will be. 



The value of p and the maximum magnetic force will determine 

 whether in Ihe ceiiire new rings wUl api>ear or respectively will 

 disappear. 



In the case one <loes not select for measurement the smallest 

 rings but if the rings /,• and ?.,■, which orujlnatt' from the sume 

 riiKi /„, are suitable to be measured, t can become larger than unity. 



When we select the i-ings thu sspeci tied the equality (4) applies ajid 

 then we may determine ;.,. and ;.„ from the angular diameters of the 

 rings and Ihe \alue of /,, i-egai'ded as known ; (he result is then 



