2 B. E. Moore 



entanglements are usually unraveled by studying the photographs 

 of two field intensities. Such a method I have pursued, but un- 

 fortunately the field strengths differed by only 20 per cent, 

 where 40 per cent difference was desirable. Sometimes the 

 overlaps are so sharp that one falls into no particular error in 

 assuming them to be the centers of two overlapping components. 

 But one can not regard this procedure as accurate as measure- 

 ments of isolated components. Neither have I regarded the meas- 

 urements upon the weaker field plates alone as accurate as the 

 other measurements. Further, they would be less accurate than 

 lines measured for both field strengths and in both first and second 

 order. All the less accurate measurements have been enclosed 

 in parentheses. 



A characteristic of the thorium spectrum is that the components 

 which vibrate perpendicular to the lines of force, the ^-components, 

 are usually narrower and sharper than those which vibrate par- 

 allel thereto, the /'-components. This was helpful in isolating the 

 j-components. The thorium lines with no magnetic field were 

 usually very sharp, but there were exceptions, and these were 

 lines which behaved peculiarly (see later). This sharpness of 

 the no-field lines led to the following method of identifying the 

 lines and components thereof for both kinds of vibrations — a 

 method which saved a great amount of labor and led to some im- 

 portant discoveries. Each set of plates was cut in two longi- 

 tudinally through the center, and the edges of the lines of either 

 the />- or ^-components brought into juxtaposition with the ends 

 of the lines upon the no-field plates in the center of the field of 

 view of the microscope. One-half of the field of view of the 

 microscope had a fixed cross wire (a diamond mark on glass) ; 

 and upon the other half of the field of view there was a movable 

 system of lines in pairs of various separations. A sharp no-field 

 line was brought under the single fixed line and the corresponding 

 s- or />-line placed as nearly symmetrical as possible therewith, 

 by hand adjustment, under the other cross-wire system, and the 

 final adjustment made by a micrometer which controlled this 

 cross-wire system. By means of another micrometer the whole 

 microscope could be moved, and by means of this motion one 



QO 



