On the Arc Spectrum of Vanadium. 



189 



" On the Arc Spectrum of Vanadium." By Sir Norman Lockyer, 

 K.C.B., F.B.S., and F. E. Baxandall, A.B.C.S. Beceived 

 March 19 —Bead March 28, 1901. 



The spectrum of vanadium is so important, especially on account of 

 the prominent part which lines of that element play in the spectra 

 of sun-spots, and the existing records of vanadium lines differ so 

 considerably, that it has been thought desirable to publish a list of 

 the lines reduced some time ago from the Kensington photographs of 

 the arc spectrum. 



These photographs were obtained by Mr. C. P. Butler with a 6-inch 

 Bowland concave grating of 21J feet focal length and 14,438 lines to 

 the inch. The region of the spectrum investigated extends from 

 A 3887 to A 4932, and occupies on the plates a length of 16 J inches. 



The sources of the spectra were (1) vanadium chloride, and (2) a 

 pure sample of vanadium oxide supplied by Sir Henry Boscoe, to 

 whom we wish to express our thanks. In each case they were 

 volatilised in the arc between poles of the purest silver which could 

 he obtained, and which were kindly placed at our disposal by Sir 

 W. C. Roberts- Austen. These are used because the number of lines 

 due to the poles themselves is so small compared with that produced 

 when carbon poles are employed, that it is much easier to detect the 

 lines really due to the substance under consideration. 



Lists of lines in the arc spectrum of vanadium have been published 

 by Bowland and Harrison,* and by Hasselberg.f The former 

 investigators used some compound of vanadium (not stated in their 

 paper) volatilised on carbon poles ; the latter employed poles made of 

 the metal itself. 



The three records naturally contain a large number of lines in 

 common, but there are many differences between any two of them for 

 which it is difficult to account. To show these differences it has been 

 considered best to give side by side in tabular form the lines in the 

 three lists, and analyse the lines special to any one list, with the 

 object of either properly establishing their claim to be accepted as 

 true lines of vanadium, or possibly tracing them to their real origin. 

 It may be safely assumed that lines common to any two of the lists 

 really belong to vanadium. 



To eliminate lines due to impurities, the vanadium spectrum has been 

 directly compared with the arc spectra of all the other elements avail- 

 able at Kensington, photographed exactly on the same scale. If the 

 "strongest" lines of an element are not represented in the vanadium 

 spectrum, apparent coincidences with any of the " weaker " lines are 



* ' Astro.-Phys. Jour.,' vol. 7, p. 273, 1898. 



f ' Svenska Yetenskaps Akad. Handl.,' vol. 32, No. 2, 1899. 



