PREFATORY NOTE 



Originally it was intended to issue the report on "Absorption 

 Spectra" and that on "Emission Spectra" separately. The publication 

 of the former was unavoidably delayed, and, in the meantime, the latter 

 being ready, the two are now combined into one volume, as Parts I and 

 II. The arrangement of the separate parts has not been altered, how- 

 ever, and the appendices, which one would naturally find at the end of 

 the volume, occur at the end of Part I, to which they belong. 



