Series Spectrum of Mercury. 639 



the ultra-red gave the following as probably forming the 



series * : — 



m. (air). 



f 1207132 



~ 1 1128816 



~ f 7082-72 



** 1 6907 93 



f 589005 



4 { 5859-59 



[ 5804-18 



n (vac). 



8281-937 



8856-527 



14115-05 



1447220 



1697317 

 17061-38 

 17224-28 



Another peculiar feature which is brought out by these 



photographs with long exposures may also be remarked on. 



It is the extraordinary complexity of the strong lines which 



form the earlier members of the diffuse series. Kayser and 



Runge observed these to be composite and to consist of 



several components, but with these long exposures in some 



cases over a score of faint satellites show on each side of the 



o 

 main line. Thus in \ 3132 a space of 50 A. units on each 



side of the main line is closely filled with them. 



This development of the series spectrum makes the series 

 of mercury in one respect more complete than those of other 

 elements. In other elements, single series may be more 

 extensively developed it is true : thus in hydrogen the diffuse 

 series has been observed down to 771 = 31, but the principal 

 series is unknown except for the first line. In sodium, Wood 

 has recently observed in the absorption spectrum the principal 

 series down to practically the theoretical limit, but only 

 seven terms of the sharp and diffuse series are knownf. 



* Ann. d. Physik, xxix. p. 662 (1909). The choice for m = 4 does 

 not fit in well with the higher lines of the series, as judged by the 

 frequency differences of their components. Below are given the wave- 

 lengths of all the linos observed in this region of the photographs which 

 are not sriven by Kavser and Runge : — 



Wave-length. 



Intensity. Wave-length. 



Intensity. 



69079 



6705-0 



6234-55 



612362 



6072-71 



3 

 2 

 6 

 2 

 1 



5872-24 

 585963 

 567614 

 5025-80 

 4995-91 



1 

 2 

 2 

 3 

 1 



t Zickendraht has, however, recently extended the number to 12. 

 Ann. d. Phys. xxxi. p. 249 (1910). 



