E. E. Lawton — Bands in ihe Spectrum of Nitrogen. 101 



Art. X. — Wave-lengths and Structural Relation of Cer- 

 tain Bands in the Spectru?n of Nitrogen; by E. E. Lawton, 

 Ph.D. 



While engaged upon a study of the spectrum of nitrogen, 

 it became necessary to photograph in juxtaposition the solar 

 spectrum and the spectrum given by the capillary portion of 

 a nitrogen Pliicker tube, which had been exhausted to about 

 l mm . Upon investigating, it was found that so little has been 

 done on this spectrum in recent years that most of the measure- 

 ments of the wave-lengths of the lines in the spectrum are far 

 inferior in precision to the measurements which can be made 

 with the instruments now available. 



The measurements of Angstrom and Thalen,*Boisbaudran,f 

 and Hasselberg,^: expressed in Angstrom units, give only one 

 decimal place ; in general, the error varies from - 2 to 0*5 of 

 that unit. Deslandres§ has published a table of wave-lengths 

 of nearly the whole negative spectrum ; but these results give 

 only one decimal place. Ames|| and Hermesdorf^f have also 

 studied the same spectrum. Ames, however, measured only 

 the second line in each band, while Hermesdorf obtained the 

 wave-lengths of six bands, particularly those of the band with 

 its head at \ 3577. The other bands measured have their heads 

 at X 3805, 3755, 3710, 3536, and 3371. These measurements 

 have been obtained with a strong dispersion, and the accuracy 

 of measurement is given as 0*01 Angstrom unit. Hermesdorf's 

 accurate investigation of the wave-lengths of a part of the 

 spectrum is the only one that the writer has been able to find 

 in the literature that brings our knowledge of the wave-lengths 

 apace with the present instruments. Hence, the object of the 

 present work has been to extend, if possible, our knowledge in 

 this direction. 



My own results have been obtained from measurements 

 made on photographs taken with a large concave Rowland 

 grating, which is installed in Sloane Physical Laboratory. The 

 grating has 20,000 lines per inch, and a radius of 21*5 ft. By 

 means of an adjustable shutter the spectrum given by the 

 capillary part of a Pliicker tube, such as is ordinarily used in 

 spectroscopic analysis, was placed side by side with the stand- 



* Acta Soc. Upsala, iii, 1875. 

 f " Spectres Ltimineux." 

 % British Association Eeports, p. 188, 1886. 



§ Comptes Kendus, ci, p. 1256, 1885; ibid., ciii, p. 375, 18S6 ; Annates de 

 Chem. et de Phys., xv, p. 5, 1888. 

 \ Phil. Mag., p. 58, 1890. 

 IT Annalen der Physik, xi, p. 161, 1903. 



