and the Rotatory Dispersion Formula. 



423 



by side on the same plate. The plate showed over 60 lines 

 in the blue-green region, some of them so faint that they 

 could scarcely be seen under the microscope of the dividing 

 engine, while others were strong enough to yield prints 

 capable of reproduction. 



Another plate was exposed and a comparison iron spectrum 

 recorded by the side of the rotation spectrum. The wave- 

 lengths of the rotatory lines were measured on both plates, 

 using the iron lines and the sodium absorption lines as 

 standards. Some of the latter were redetermined, as it was 

 found that they were much sharper when the sodium was 

 heated in a high vacuum, than when heated in hydrogen, as 

 in the previous work by Dr. Moore and the writer. A print 

 obtained from the plate on which the rotatory spectrum 

 and absorption spectrum were recorded, is shown on Plate V. 

 fig. 5. The absorption spectrum is above. Many lines 

 are, of course, visible on the negative which do not show 

 on the print. The rotatory lines in many cases coincide 

 with the heads of the groups of absorption-lines, though the 

 centre of the line appears to be slightly displaced beyona 

 the head of the group of absorption-lines. The displacement 

 is, however, very slight, not more than half the width of the 

 line. A list of the wave-lengths of all the lines visible on the 

 negative follows. The approximate intensities are repre- 

 sented by numerals, 10 indicating the maximum intensity 

 and 1 the minimum. Lines marked with an interrogation 

 point were so faint as to be doubtful. 



Green Rotation Spectrum 



1 



5225-34 



1 



5033-54 



2 



4839-56 



1 



5218-49 



1 



5025-66 



9 



4837-49 



1 



5212-02 



1 



5003-12 broad 



2 



4819-43 



1 



5186-70 



10 



5001-57 



1 



4814-60 



1 



5179-71 



5 



4979-34 



1 



4812-68 



1 



517298 



1 



4970-85 



3 



4810-16 





5171-98 



1 



4967-10 



3 



4802-62 



1 



516904 



1 



4964-39 



5 



4792-67 





5165-85 



9 



4962-85 



3 



4782-89 



1 



5140-71 



1 



4958-62 



1 



4777-00 



2 



5133-73 



1 



4933-93 



1 



4766-94 



2 



5126-54 



3 



4932-64 



(> 



4756-69 



1 



5119-34 



o 



4924-32" 



1 



475204 



2 



5094-78 



4 



4912-10 



2 



4738-51 



7 



5087-31 



1 



4904-67 



4 



4727-52 



8 



5079-78 



1 



4903-38 



1 



4716-90 



1 



5071-58 



1 



4896-65 



1 



4715-63 



1 



5052-83 



1 



4894-58 



1 



4703-78 



1 



5049-56 



1 



4892-77 



2 



4692-54 



3 



5048-49 



2 



4883-81 



2 



4670-30 



7 



5040-65 



o 



4865-59 





- 



