University Studies 



Vol. IX APRIL iqo 9 No. 2 



I. — The Separation of the Spectral Lines of Thorium in the 

 Magnetic Field 



BY B. E. MOORE 



PART I. INTRODUCTION, EXPERIMENTAL METHOD, AND PECULIAR 

 FEATURES OF THE THORIUM SPECTRUM. 



The spectral photographs of this substance were taken during 

 the winter semester of 1907 at the physical institute of the Uni- 

 versity of Gottingen at the suggestion of the director, Prof. W. 

 Voigt, who courteously placed all the necessary equipment at my 

 disposal and enthusiastically promoted the investigation. This 

 was at the time I studied the spectra of barium, yttrium, zirco- 

 nium, and osmium (Univ. Studies, Jan. 1908). The thorium lines 

 were found to be too numerous and entangled to admit of ready 

 identification and were therefore laid away for study at a more 

 opportune time. A component or more of a line is frequently 

 found between the components of another line. Two components 

 of different lines may lie so close together that one can tell with 

 difficulty to which of the two lines they may belong; or two or 

 more components may overlap. These overlaps are of various 

 degrees, i. e. in one extreme they may be merely touching each 

 other and form one broad line ; or in the other extreme be accu- 

 rate duplicates in position, and produce an intensified sharp line. 

 How complicated this becomes may be illustrated by one small 

 region, six Aengstrom units wide, about the separation of D x and 

 D 2 , where there were found components of thirteen lines. These 



University Studies, Vol. IX, No. 2, April 1909. 



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