PROF. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 93 



B = 24558 



N/-I m+ '89484-1 I (m = 3.4.5) 



II ml 



E 1 = S l (oo) + 2 v -VP I (m) 



(m = 4.5.6) 



E 2 EE h ( oo ) + 3v 



G = 27034-5-N/-Uz+-8358 + } (m = 2.3.4) 

 /I m J v 



C?= 23491'5-N/(m + 1-3398- - V*. 

 / L m J 



All the terms in a/m have little significance, as the lines are too- uncertain to 

 enable a. to be determined with any approximation. The only lines not allocated are 

 LENARD'S 4820, 4730, which have not been seen by any other observer. 



Comparison of the Different Elements. The first certain result is the appearance 

 of a strong well-developed series in the ultra-red, whose limit depends on the value of 

 VD (2), giving doublet series when VD has two values as in Cs. The limits, as 

 calculated from three observed lines, differ from the exact values of VD by amounts 

 increasing from Na to Cs in somewhat the same way as in the corresponding cases of 

 VP (1) and S ( oo ), and will probably be accounted for in a similar way. If the limits 

 are taken to be VD (2) exactly, the resulting formulae are of the D type, as found 

 from two lines. Na and K give the D type, Rb and Cs the S type. 



The observations are not sufficiently accurate to definitely settle this question. 

 Under the circumstances it may be best to use RYDBERG'S formulae, i.e., a = 0. In 

 this case the ju, is always not far from unity, and the limits are closer to VD (2). The 

 values of /JL for Na, K, Rb, Cs come out respectively '998(5, '9965, '9798, '968, the 

 first two only being reliable as deduced from PASCHEN'S observations. Taking 

 his estimates of observational errors, the values for Na and K are respectively 

 998610- -000343p+'002986<7 and '996648 -'0005 19/>+ '000735c/ where p, q are the 

 fractions of his possible error. 



It is seen that they may possibly be equal, and the possible errors for Rb and Cs do 

 not contradict, that they also may have the same p. say, about '997. Its possibility, 

 also, may be further illustrated by finding the difference of wave-numbers between 

 the lines of K, Rb, Cs for m = 3 and m 6, which have been measured for all three. 



K 11222'84l-26/>-6592'00'87 = 4630'8421, 



Rb 12087-17l-46&-7437'36-53& = 4649'8l32, 



Cs 14554'228 -9871'92'97& = 4682'3024, 



b denotes B.'s possible error. It has been taken about 16 his actual error 



as against PASCHEN in KF (4). 



