Investigation of Superficial Resonance of Sodium Vapour, 1033 



The law of the partition 'of energy in spectrum lines 

 furnished by the kinetic theory of gases is 



!/=Ce- L '% (1) 



in which y is the intensity at a distance equal to x from the 

 centre of the line (at which point the intensity is C), and 

 h gives us the rate at which the intensity falls off as we 

 depart from the centre. 



Fiar. 4. 



The width 2e of a spectrum line, as defined by Fabry and 

 Buisson, is the distance between two ordinates at distances e 







from the centre, of value equal to ^ 9 u e. an intensity one- 

 half as great as that at the centre of the lin 



This gives us 



Ce 



<J 



and 



-fee 



= 2 



e. 



or 



v //:e= v /log2. 



.... (2) 



The total intensity of the line being the area comprised 

 between the curve and the axis of abscissa?, we have 



-I 



cv 



^\1 X J ] ^ 



x/k 



(3) 



If we assume that the portion of the exciting line effective 

 in exciting the resonance is comprised between the ordinates 

 situated at — #j and -\-x v (which is of course an approxi- 

 mation since in reality the exciting portion of the line is- 

 as shown by the dotted curve of fig. 4), we have, for the 



