1902.] 



some Lines in the Spectrum of Lithium. 



167 



Some photographs were also taken of the spectrum of the trans- 

 parent flame which issued from the arc, the bar magnet being used as 

 above. With a short exposure one narrow bright line was obtained of 

 wave-length 4603*06 ; with a longer exposure this bright line was 

 much stronger, and there was the appearance of a weak line on its 

 more refrangible side, exactly as Professors Liveing and Dewar described. 

 The wave-lengths of these two were 4603*18 and 4601-89 respectively 

 on one photograph (5 in figure), and 4603*12 and 4601*65 on another. 

 The last line was fairly sharp on the less refrangible side, whilst it faded 

 gradually on the other side (6 in figure). With still longer exposures 

 the weaker line could not be distinguished from the wing of the much 

 expanded bright line. This wing when weak always resembles a line, 

 and it was thought that a line might be nearly coincident with its less 

 refrangible edge. Measurements showed that this edge varied in 

 position on different photographs, but Professor Liveing suggested 

 that the tip might be formed by a line, and if so, the tip should 

 always have the same wave-length. The following table gives the 

 wave-lengths of the two tips on different photographs : — 



Spectrum. 



Tip of weaker 

 side. 



Tip of stronger 

 side. 



206 :i 



4601 *68 





213 4 



•83 



4603 -11 



213 r> 



■66 



•11 



214 1 



•72 



•03 



222 6 



•78 



•10 



222' 



•82 



•11 



224° 



•82 





226 5 



•83 





226' 



•95 



4603 -21 



232 fi 



•79 





This evidence is not conclusive ; both tips appear to vary, but 

 the weaker one varies more than the other. The arc, in these ex- 

 periments, was formed with a Gulcher lamp with the carbons vertical, 

 the positive being uppermost, and the image of the arc projected 

 on to the slit of the collimator by a lens. It was observed that the 

 less refrangible point, wave-length 4603*1, was, in many photographs, 

 higher on the plate than the weaker point ; it was given out by 

 vapour quite near to the positive pole. It was observed also in 

 some photographs that the line extending from it faded away lower 

 down; the vapour near the negative pole did not emit this line 

 but gave the broad bright line with the broad dark line down its 

 middle. This broad bright line fades away as the positive pole is 

 approached ; the more refrangible wing ends in a point, but the less 



vol. lxxi. o 



