[ 49 ] 



IV. A New Table of Standard Wave-lengths. 

 By Prof. Heney A. Kowland *. 



DURING- the last ten years I have made many observa- 

 tions of wave-lengths, and have published a preliminary 

 and a final table of the wave-lengths of several hundred lines 

 in the solar spectrum. 



For the purpose of a new table I have worked over all my 

 old observations, besides many thousand new ones, principally 

 made on photographs, and have added measurements of 

 metallic lines so as to make the number of standards nearly 

 one thousand. 



Nearly all the new measurements have been made on a 

 new measuring-machine whose screw was specially made by 

 my process f to correspond with the plates and to measure 

 wave-lengths direct with only a small correction. 



The new measures were made by Mr. L. E. Jewell, who 

 has now become so expert as to have the probable error of 

 one setting about Yoi~o division of Angstrom, or 1 part in 

 5,000,000 of the wave-length. Many of these observations, 

 however, being made with different measuring-instruments, 

 and before such experience had been obtained, have a greater 

 probable error. This is especially true of those measure- 

 ments made with eye-observations on the spectrum direct. 

 The reductions of the readings were made by myself. 



Many gratings of 6 in. diameter and 21J ft. radius were 

 used ; and the observations were extended over about ten years. 



The standard wave-length was obtained as follows : — 

 Dr. Bell's value of D 1 was first slightly corrected and became 

 5896*20. C. S. Peirce's value of the same line was corrected 

 as the result of some measurements made on his grating 

 and became 5896*20. The values of the wave-length then 

 become : — 



Weight. 



Observer. 



D. 



1. 



2. 

 2. 



5. 

 10. 





5895-81 

 5896-25 

 5895-90 

 5896-20 

 5896-20 



Miiller & Kempf 



Kurlbaum 



Peirce 



Bell 







Mean 



5896-156 





* Reprinted from a separate copy from the ' Astronom. and Astero- 

 Physics ' communicated by the Author. 



t See JEncyc. Brit., art. Screw. 

 Phil. Mag. S. 5. Yol. 36. No. 218. July 1893. E 



