148 



Ëence 



ƒ• 



by whicli we can calculate tlie maximum absorption index /*„ . 



For this purpose we develop e~-''^ in a series and integrate 

 between the limits v = — oo and r = -|- go, after having substituted 

 tor ]i the value (24) and replaced cU by ).„ dr. Putting 



we find 



V 2n u 



Widi the values « = 1,88.10^ cm/sec and ;i„ = 5893 A. U. the 

 quantity on the right hand side of this equation becomes 1,50 and 

 we tind 



.r = 2/*„(f=4,l 

 approximately, showing that the absorption at tlie middle of the line 

 must have been niore than 98°/„. As rf=2 cm., the index of 

 absorption itself is found to be about 



;i„ = l,02Ve™. 



^ 11. Now this value is widely diiferent from the one that follows 

 from (26). At 89° C. the pres.sure of iodine vapour is about 24 mm. 



Using this value and |.ut1ing ;„ = 5893 A.U., 7*= 362, J/ = 254, 

 we get from (26) 



h, = 1,9 . 10- 7,n,. 



Tlie great difference between tliis number and the former one 

 may be accounted for by supposing that a very small part (about 

 one twenty millionth) only of the molecules are active in producing 

 the absorption, so far as one line is concerned, a conclusion agreeing 

 with that to which one has been led by other lines of research. 



It must however be remarked that perhaps the fundamental sup- 

 position expressed in equation (1) does not correspond to reality and 

 must be replaced by a more general one. Instead of thinking of a 

 vibrating negative electron we may simply suppose that imder the 

 influence of the incident light an alternating electric moment p is 

 induced in a particle. Equation (1) then takes the form 



p + «p 4- /Jp = yE 



in which «, /?, and y are certain constants, the first of which deter- 

 mines the resistance, while /? has the value ?i/. We ore again led 

 to equation (24), but instead of (25) we get an expression which 



