lL. E. Lawton — Bands in the Spectrum of Nitrogen. 105 



3958870 3954-017 3949'259 



3957-392 3952-254 3948'826 



3956-932 3951-866 3946'972 



•482 -457 '562 



3954-892 3949*694 -173 



•419 



To Deslandres* we owe most of our knowledge of the laws 

 governing the bands in the nitrogen spectrum, and the lines 

 in a band. These laws, three in number, are briefly as follows : 



1. In a given band the interval from one line to the follow- 

 ing in any series, calculated in vibration numbers, are in arith- 

 metical progression, i. e., the lines are connected by a relation 

 of the form, 



— — =T$=a + bn? 



A 



where a and b are constants, and n is a series of positive 

 integers. 



2. When two or more series arise from the edge of a band, 

 they are similar in all respects, and all bands belonging to the 

 same substance have the same number of series. 



3. In a series of bands the vibration numbers of the edges 

 form a series similar to that of the line in a single band. 



"With these laws as a basis, Deslandresf has, quite recently, 

 investigated the band at \ 3577 in the second group of the 

 negative spectrum. He finds that there are seven series of 

 lines and all can be expressed by the formula 



= A ('«+£> 



where A, c, p, q, are constants, and m a series of integers. 

 The application of the formula to the wave numbers of a band is 

 not given by Deslandres, hence the above measurements furnish 

 an opportunity for the application of the formula. Taking 

 the band beginning A 3998, the formula has been applied to the 

 triplets of the tail. The constants have been determined by 

 the method of trial and error giving the following formulae : 



1st line of triplet. 



N = 2501 -457 + 0-0251257(m + 0-85) 2 



. 2d line of triplet. 



N = 2502-145 + 0*025296(m + 0-5) 2 



3d line of triplet. 



N = 2502-786 + 0-02490(m + 0'5) 2 



* Comptes Eendus, ciii, p. 375, 1886. Annales de Chemie et de Physique, 

 xv, p. 5, 1888. 

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



