102 E. E. Lawton — Bands in the Spectrum, of Nitrogen. 



arc! spectrum. The solar spectrum, with Rowland's values, was 

 used as the standard, and the unknown wave-lengths were 

 obtained by interpolation. The nitrogen tube had been ex- 

 hausted to about l mm . Many photographs were obtained with 

 exposures varying from forty-five to ninety minutes, the longer 

 time always giving the best results. These photographs* show 

 for this spectrum a complicated structure. The heads of bands 

 lie toward the red, with the tails extending up the spectrum, 

 and the lines of the bands are degraded on the side toward the 

 head. Each band offers at the head an intense triplet. In the 

 bands measured, the second and third lines of this triplet are 

 clearly doubles, and it is quite probable that the head of the 

 band which forms the first line of the triplet is a double also. 



Considering a single band — near the head there is a confu- 

 sion of lines showing no regularity of intensity ; but as the 

 lines become more and more remote from the head, the lines 

 are seen to be grouped in series of threes, or triplets, and while 

 the distance between the lines of a single triplet diminishes 

 the distance between triplets increases. The lines of each trip- 

 let show the same intensity, which gradually diminishes with 

 an increase of distance from the head until they finally dis- 

 appear, or, as is sometimes the case, become hidden in the next 

 band. The irregularity of intensity shown by the lines near 

 the head has been pointed ont by .Deslandres,f using the band 

 X 3577, as due to several secondary series, if I may be per- 

 mitted to call them such, which are quite distinct from those 

 series of lines which form the triplets of the tail. To these 

 secondary series belongs the strong triplet seen in the head of 

 each band. In the same paper Deslandres considers that the 

 third line of the triplets in the tail is a double, but I have seen 

 no indications that this is so, and neither do Hermesdorf's^: 

 measurements indicate this to be the case. 



The second group of this spectrum extends from A 5000 to 

 A. 3000 and is made up of five series of bands.§ All except 

 the lower part of this group has been photographed during 

 this investigation. The first attempt to secure a photograph of 

 the lower part showed some faint lines at about A. 4600, but a 

 later attempt proved unsuccessful, owing to the weakening of 

 the tube. Eye observations, however, showed some strong 

 lines in this lower region. Using the photographic method, 

 some good jjlates of the region X4200 to X3000 have been 



*It niay be worthy of remark here, as a matter of interest, that there are 

 no telluric lines in the solar spectrum corresponding to the lines of this 

 nitrogen spectrum. Nothing more than what might be termed accidental 

 coincidences were observed. 



f Comptes Rendus, cxxxviii, p. 317, 1904. 



% Loc. cit. 



§ Comptes Rendus, ciii, p. 375, 1886. 



