I 



Table 322. 

 SPECTRUM SERIES. 



275 



The flame spectrutr. lines of the elements are comparatively few. These remain prominent in the arc with the appear- 

 ance of many more. In the spark the typical arc lines tend to disappear with the appearance of entirely new lines. 

 Those thus intensified or only appearing in the violent action of the condensed spark have been called "enlianced " lines. 

 This order of development may be taken as one due to increasing temperatures. The spectra of compounds are invaria- 

 bly banded; different sets of bands indicate oxides, chlorides, etc. Banded spectra of the elements are generally assumed 

 to be due to molecules, the simpler spectra to atoms, and the enhanced spectra to atoms with one electron lost (ionized.) 

 The enhanced spectrum of He is similar to that of H except that the wave-lengths are shortened because of the increased 

 attraction of the heavier nucleus, 2e in place of e. 



In the spectra of many elements and compounds certain lines or groups of lines (doublets, triplets, etc.) occur in or- 

 derly sequence, each series with definite order of intensity (generally decreasing with decreasing wave-length), pressure 

 effect, Zeeman effect, etc. Such series generally obey approximately a law of the form 



where v is the wave-number in vacuo (reciprocal of the wave-length \) generally expressed in waves per cm; m is a varia- 

 ble integer, each integer giving aline of the series; L is the wave number of the limit of the series im = oo); A^, the "Uni- 

 versal Series Constant"; and i? is a function of m, or a constant in some simple cases. 



Balmer's formula (1885) results if L = N/n-, where n is another variable integer and R= o. Rydberg's formula (1S89) 

 makes R a constant, and L is not known to be connected with A''. Other formulae have been used with more success. 

 Mogendorff (1906) requires R = constant/wt, while Ritz (1903) has R = constant/m^. Often no simple formula fits 

 the case; either R must be a more complex function of m, or the shape of the formula is incorrect. 



Bohr's theory (see also Table 515) gives for Hydrogen. 



N= {2nime'{Sf+m)j /Mh\ 



where e and m are the charge and mass of an electron, M the atomic weight, and h, Planck's constant. The best value 

 for N is 109678.7 international units (Curtis, Birge, Astrophys. J. 32, igio). The theory has been elaborated by Som- 

 merfeld (Ann. der Phys. 1916), and the present indications are that Af is a complex function varying somewhat from 

 element to element. 



Among the series (of singles, doublets, etc.), there is apt to be one more prominent, its lines easily reversible, called 

 the principal series, P(m). With certain relationships to this there may be two subordinate series, the first generally 

 diffuse. Dim), and another, Sim). Related to these there is at times another, the Bergmann or fundamental series, Bim). 

 or Fim). m is the variable integer first used above and indicates the order of the line. 



The following laws are in general true among these series: (i) In the P(f») the components of the lines, if double, 

 triple, etc., are closer with increasing order; in the subordinate series the distance of the components (in vibration 

 number) remains constant. (2) Further, in two related Dim) and Sim), Av (vibration number difference) remains 

 the same. <3) The limits (i) of the subordinate series, D(»«) and 5(f«), are the same. (4) Af of the subordinate series 

 is the same Ac as for the first pair of the corresponding P(m). (5) The limits iL) of the components of the doublets 

 (triplets, etc.) of the Pirn) are the same. (6) The difference between the vibration numbers of the end of the P{m) 

 and of the two corresponding subordinate series gives the vibration number of the first term of the Pirn). The first 

 line of the Sim) coincides with the first line of the Pirn) (Rydberg-Schuster law). The limit of the Bergmann or funda- 

 mental series is the first term of the diffuse series (Runge law). 



In the spectrum of an element several of these families of series Pirn), Dim), Sim), Bim) may be found. For further 

 information see Baly's Spectroscopy and Konen's Das Leuchten der Gasen, 1916, from the latter of which is taken the 

 j following tables, based greatly upon Dunz's Die Seriengesetze der Linienspektra, Diss., Tubingen, 191 1, which has 

 also appeared in book form, Hirzel, Leipzig. 



The "complexity" of the lines of a series is constant throughout a column in the periodic table, varying from one col- 

 umn to another. The displacement law of Kossel and Sommerfeld states that when an element is ionized (losing an elec- 

 tron) the enhanced spectrum takes on the same type of "complexity" as the arc spectrum belonging to the element of 

 the preceding column (to the left) but with lines shifted to a higher frequency. If two electrons are lost, the displace- 

 ment is two columns to the left. If the outer ring has an odd number of electrons the spectrum will consist of: doublets; 

 if even, of triplets and singlets. 



(discussion continued on page 441) 



Series Spectra of the Elements. — The ordinary spectrum of // contains 3 series of the same kind: one in the ultra- 

 violet region; Schumann region, v = ATC/i- — '/"'). «> 2. 3 ■ • •; one in the visible, c = Ni^/i''- — '/"")> ''. 3, 4, 5 ■ • •; 

 and one in the infra-red, v = Ni'/i- — '/»"). n, 4, $, 6 . . . He has three systems of series, one 'enhanced," including 

 the Pickering series formerly supposed to be due to H. The next two tables give some of the data for other elements. 



Sesjes Sysi£M or Poxassiuu. 



Smithsonian Tables. 



