288 PROCEEDINGS OP THE AMERICAN ACADEMY 



XVIII. 



CONTRIBUTIONS FROM THE JEFFERSON PHYSICAL 



LABORATORY. 



WAVE-LENGTHS OF METALLIC SPECTRA IN THE 



ULTRA VIOLET. 



By John Trowbridge and W. C. Sabine. 



Presented March 14, 1888. 



PART I. 



Introduction! 



The Catalogue of Metallic Spectra, revised by a Committee of the 

 British Association, and published in its volumes for 1885 and 1887, is 

 an extremely valuable contribution to the subject of spectrum analy- 

 sis ; it contains the material for future generalization in regard to the 

 molecular structure of so-called elements, or in regard to the harmonic 

 relations which may exist between their wave-lengths. Here can be 

 found in juxtaposition the results of various observers upon the metal- 

 lic spectra of the same metal, and the student can judge of the relative 

 accuracy of the results. A superficial inspection of this Catalogue will 

 show that even distinguished observers, like Thalen and Kirch hoff, 

 often differ in their results by one part in 4,000, or one part in 2,500. 

 No observer of metallic spectra gives results to more than one tenth 

 of Angstrom's unit, or to more than one tenth of one wave-length. 

 Physical science, however, now demands a greater degree of accuracy. 

 Various hypotheses in regard to the apparent coincidences between 

 lines of metallic spectra and lines in the solar spectrum have been pro- 

 pounded, and can only be settled by more accurate measurements of 

 wave-lengths. There are also questions constantly arising in regard 

 to the displacement of lines of spectra due to the motion of the stars 

 and to changes of temperature, which require a greater degree of accu- 

 racy in the measurement of wave-lengths of gaseous and metallic spec- 

 tra than the results of previous observers afford. It may be remarked, 

 that observations upon the metallic spectra of metals from the limits 

 of the visible red to the limits of the visible violet have become com- 



