Dispersion in Relation to the Electron Theory. 247 



Taking w (5461) = 1*3345 and n (4359) = 1*3402, formula (9) gives 

 X 1 = *113/Lt, a value agreeing well with the above. 



A small but decided progression is apparent in the values 

 of X 1? which points to the existence of at least two free- 

 periods responsible for the dispersion in water. The smallness 

 of the progression is probably due to the value of X x being 

 small in comparison with the shortest X of the experiments, 

 and for the same reason the longer free-period cannot be 

 calculated with accuracy from equation (10). The mean 

 value obtained from observations acf and beh is approxi- 

 mately -1375/a, which gives ^ = *9499 and & 2 = *7012. Thus 



^Xl0 14 = -9499/ 7; j^- 2 y + *7012, V- '01891. 



The differences between the values of <£ calculated from this 

 formula and the observed values are given in the last 

 column. 



Fiatow * finds that the natural dispersion in water is very 

 accurately represented by an equation of the form (3) from 

 •589 to *214 iu ; the constants for 20° C. being : 



a = -37512 c = -013414 



a, = -38850 \ x = -12604. 



As \ x is here an effective mean value, this result agrees 

 well with the deduction made above, namely, that the 

 dispersion in liquid water is controlled by a period near 

 \ = -1375 and at least one other of smaller value. 



The following table gives the values of the magnetic 

 rotation (8) relative to the value for '4958/x for a number of 

 lines in the ultraviolet spectrum of iron. The only previously 

 obtained values — those of Landauf — obtained with an electro- 

 magnet of small power, and recorded to three significant 

 figures, are worked out as ratios for comparison. 



\xio-*. 



S (Landau). 



d (Author). 



•4958 



1000 



1-000 



•4529 



1-226 



1-221 



•4405 



1-301 



1-299 



•4308 



1-366 



1-365 



•4199 



1-4-16 



1-449 



•4046 



1-575 



1-576 



•3886 



1-737 



1-733 



•3609 



2065 



2060 



•3100 



3005 



3017 



* Ann. d. Phys. (12) p. 85 (1903). 

 f Phys. Zeits. (13) p. 417 (1908). 



