352 Wave-lengths of Metallic Spectra in the Ultra-Violet, 

 Table (continued). 



1. 



2. 



Wave- 

 lengths of 

 copper lines. 

 Spark. 



3. 



Hartley 



4. 



5. 



Liveing and 



6. 



7. 



Intensity. 



and 

 Adeney. 



Corrections. 



Dewar 

 Arc. 



Corrections. 



Intensity. 

 B.A. 



2 



2037-3 













2 



2036-0 













1 



2030-9 













2 



2025-7 













1 



2016-9 













1 



2015-8 













1 



20132 













2 



1999-9 













2 



19894 













2 



1979-4 













1 



1970-4 













1 



19441 













Conclusions. 



It will be observed that the corrections to be applied to 

 the wave-lengths obtained by Liveing and Dewar are pro- 

 gressive in their nature when compared with those which 

 must be applied to the results of Hartley and Adeney. The 

 difficulty in identifying lines and determining coincidences 

 by employing the tables of metallic spectra in the ultra- 

 violet, published by the British Association, is illustrated by 

 our work ; for certain lines measured by Liveing and Dewar, 

 which are identified by the committee with lines given by 

 Hartley and Adeney, are in reality removed from each other, 

 one or two lines intervening. In certain cases the lines of 

 Liveing and Dewar are wholly beyond identification with 

 those given by Hartley and Adeney. 



The results of our inquiry into the accuracy of the results 

 of previous observers in measuring wave-lengths of metallic 

 spectra in the ultra-violet can be summed up as follows : — 



1. We believe that the method of photographing images 

 of the slit upon the photographic plate, due to Cornu, in 

 order to determine positions, leads to unavoidable errors. 



2. The best method of determining wave-lengths of metallic 

 spectra is by the use of concave gratings ; for linear measure- 

 ments are substituted for angular ones, underlying spectra 

 are brought to the same focus as overlying spectra, and, 

 since a great number of lines are in focus on the same plate, 



