of the Lines of the Solar Spectrum. 259 



increases his value by about 1 in 7700 ; thirdly, on a result 

 obtained in my laboratory with two of my gratings by Mr. 

 Bell, which is published with this paper. Mr. C. S. Peirce 

 has kindly placed his grating at our disposal ; and we have 

 detected an error of ruling which affects his result and makes 

 it nearly coincide with our own. The wave-length of the 

 mean of the two E lines is — 



Angstrom (Atlas) 5269-12 ±"05 



(Corrected by Thalen) . . 5269-80* 



Peirce 5270-16 



„ (Corrected by Rowland and Bell) 5270*00 



Bell 5270-04 



These results are for air at ordinary pressures and tempera- 

 tures. The last is reduced to 20° C. and 760 millim. pressure. 

 To reduce to a vacuum, multiply by the following : — 



Fraunhofer line A. C. E. Gk H. 



Correction-factor .. 1-000291 1-000292 1-000294 1-000297 1*000298 



The relation between my wave-lengths and those of 

 Angstrom are given by the following, Angstrom's values 

 being from p. 31 of his memoir : — 



o 



Angstrom 



Eowland 



A (edge). 

 .... 7597-5 

 .... 7593-97 



.... -35 



D 2 . 



.... 5895-13 

 .... 5896-08 



B (edge). 

 6867-10 

 6867-38 



6717-16 

 6717-83 



0. 



6562-10 

 6562-96 



6264-31 

 6265-27 



Difference 



o 



Angstrom 



Eowland 



•28 



D v 



5889-12 

 589012 



•67 



570845 

 570956 



•86 



Peirce's line 

 5623-36 

 562470 



•96 



i. 

 5454-84 

 5455-68 



Difference 



o 



Angstrom 



Eowland 



•95 



Tjl 



.... 5269-59 

 .... 527043 



1-00 



E 

 5268-67 

 526965 



111 



K 



518310 

 5183-73 



1-34 



5138-78 

 5139 47 



•84 



F. 

 4860-74 

 4861-43 



Difference 



o 



Angstrom 



Eowland 



•84 



.... 4702-44 

 .... 470311 



•98 



G. 



4307-25 

 4307-96 



•63 



•69 



•69 









Difference 



•67 



•71 





The greatest variation in these differences is evidently due 

 to the poor definition of Angstrom's grating, by which the 

 numbers refer to groups of lines rather than to single 

 ones. Selecting the best figures, we find that Angstrom's 

 wave-lengths must be multiplied by 1*00016 to agree with 

 Bell's, while the correction for Angstrom's error of scale 

 would be 1-000110. 



* Sur le Spectre du Fer, Thalen. 

 T2 



