1906.] on Recent Progress in Magneto-Optics. 299 



My first measurements already made it evident that lines of 

 different series behaved entirely unlike each other. * Hence the 

 ratio of charge to mass could not be the same for all vibrating 

 electrons. 



Runge and Paschen have proved in a most beautiful and system- 

 atic investigation f that all the lines of a trunk or of a branch behave 

 in the same manner. This result was first announced by Thomas 

 Preston,! but it is not stated to what degree of accuracy and for how 

 many lines he investigated the subject. 



AH lines of the same series are split up in the same manner, e.g. 

 all lines are resolved into triplets or all into nonets. Moreover, not 

 only the general type of sub-division is the same, but even the 

 amount of separation, when measured in oscillation frequency. 



The second law discovered by these physicists is this : That 

 corresponding series of different elements show the same type of reso- 

 lution, and the amount of separation is the same when measured on 

 the frequency scale. 



In the alkalies, each line of the trunk series is double, and we 

 may speak of a twin trunk. The yellow sodium lines are a typical 

 example. The type of resolution of the two lines is shown in the 

 diagram. (Fig. 20.) Here we have again our old sodium lines in the 

 field. The same division occurs in all cases when twin trunks exist. 

 Substances so different in chemical behaviour as sodium, copper, 

 silver, and calcium (e.g. the well known lines H and K), split up 

 in the same manner. And I think that even Sir William Orookes 

 will be surprised to hear that his thallium lines are in the magnetic 

 field only counterfeit sodium lines. I can show you the splitting 

 up of these beautiful thalUum lines in the slide. (Figs. 21 and 22.) 



With zinc, cadmium, mercury, calcium, there are three main bran- 

 ches associated with each other. The amount of separation is the 

 same in each of these branches. The type of resolution is shown in 

 the diagram. (Fig. '2'd.) I can show you further lines of mercury, 

 the triplet, the sextet, the nonet. Another example of the same 

 sextet is given by a zinc line. The next slide refers to some beauti- 

 ful magnesium lines, exhibiting the same three types of resolution. 

 (Fig. 24.) 



We see that in these cases the simple image of an oscillating elect- 

 ron does not apply. I regret to say that the electronic theory cannot 

 yet give us the explanation of the more complicated resolutions, even 

 for the quartet, we are yet in want of a model. 



* Zeeman. Verslagen Ak. v. Wetenschappen, Amsterdam, December, 

 1897. Phil. Mag., February, 1898. 



t Runge and Paschen. Berl. Akad. Abhandlungen, Anhang, 1902. Sitzbe- 

 richte, Berlin, p. 380, p. 720, 1902. Runge. Physik Zeitschr., 3. Jahrgang, S. 

 441. Kayser. Spektroscopie. Band 2. Kapitel IX., 1902. 



; Preston. Dublin Trans. (2) 7. p. 7-22, 1899. 



