Separation of the Spectral Lines of Thorium 15 



solved types, which would probably separate with stronger field. 

 The unresolved lines of thorium have generally a different ap- 

 pearance, and most of them are probably of an inseparable type. 

 There are a few of these lines distributed throughout the spec- 

 trum, but the most of them are found in the small region of Table 

 XIX. 



Comparison of the intensities of the s- and ^-components with 

 the corresponding no-field lines showed that there was no uni- 

 formity in their ratio to the intensities of no-field lines, and there- 

 fore no uniformity in their ratio to each other. It is a well-known 

 fact that the exposure of the plates must be many times longer 

 when the spark is in the magnetic field. Possibly, it is equally 

 well known that the relative intensities of the lines change in the 

 magnetic field. This is attributed to- the change in the character 

 of the spark. In the simplest theory of the triplet the ^-compo- 

 nent is supposed to be half the intensity of the /"-component. Ob- 

 servation shows cases where the intensities are the reverse. When 

 one considers an unseparated line, the simplest assumption would 

 be that the field would change p- and ^-components relatively the 

 same, and that the intensity of the vibrations parallel and per- 

 pendicular to the lines of force would be the same. However, in 

 comparing the p- and ^-components with the no-field line inten- 

 sities and with each other, the ratio of their intensities was found 

 to vary in the same way as observed in the triplets. From a com- 

 parison of many lines one might infer that the /'-exposures are 

 at least 25 per cent stronger than the ^-exposures. But here, one 

 may assume any value less than twofold, for the relative expo- 

 sure of the p- and ^-plates, and then will find only a small num- 

 ber of the lines to have equal intensity for both j- and p-expo- 

 sures. The inference seemed to be that the lines were not 

 vibrating with equal intensity parallel and perpendicular to the 

 lines of force. I soon found there was a tendency for some of 

 these lines to group themselves into pairs, i. e. for one line there 

 was a greater luminosity perpendicular to the lines of force than 

 parallel thereto, and for an adjacent line or close companion the 

 phenomenon was reversed. This reminds one of the close com- 

 panionship of many of the triplets. There are cases where sev- 



103 



