;<_( DR. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 



\V .lenotes the atomic weight, w = W/100. 

 8, denotes the "oun" = 90-47^. 

 S, n&i, but S is used for & 4 = 361 89w*. 



- C is used for the difference in wave-length between an observed line and its calculated value. 

 O denotes the maximum possible error of observation. 



In gtnrrnl, figures in brackets before lines denote intensities, and in brackets after, possible errors of 

 observation. 



THE doublet and triplet separations in the spectra of elements are, as has long been 

 known, roughly proportional to the squares of their atomic weights, at least when 

 elements of the same group of the periodic table are compared. In the formulae 

 which give the series lines these separations arise by certain terms being deducted 

 from the denominator of the typical sequences. For instance, in the alkalies if the 

 ja-sequence be written N/D ra 2 , where D m = m + n + a/m, the ^-sequence for the second 

 principal series has denominator D A, and we get converging doublets; whereas 

 the constant separations for the S and D series are formed by taking 

 S, ( oo ) = D, ( oo ) = N/D, 2 and S 2 ( oo ) = D 2 ( oo ) = N/(D, - A) 2 . It is clear that the 

 values of A for the various elements will also be roughly proportional to the squares 

 of the atomic weights. For this reason it is convenient to refer to them as the 

 atomic weight terms. We shall denote them by A in the case of doublets and A, 

 and A 2 in the case of triplets, using v as before to denote the separations. Two 

 questions naturally arise. On the one hand what is the real relation between them 

 and the atomic weights, and on the other what relation have they to the constitution 

 of the spectra themselves ? The present communication is an attempt to throw some 

 light on both these problems. 



The Dependence of the Atomic Weight Term on the Atomic Weight. 



The values of the A can be obtained with very considerable accuracy, especially in 

 the case of elements of large separations, i.e., of large atomic weight. If, therefore, 

 the definite relation between these quantities can be obtained, not only may it be 

 expected to give some insight into the constitution of the vibrating systems which 

 give the lines, but it may afford another avenue whereby the actual atomic weights 

 of elements may be obtained, and the solution of the problem is therefore of importance 

 to the chemist as well as to the physicist. 



t may be interesting to note the steps which first led the author to the solution 



vhich follows, and incidentally may add some weight to the formal evidence in its 



has long been known that in the case of triplets the ratio of A, : A 2 is 



slightly larger than 2. It was natural, therefore, in an attempt to discover 



ion to the atomic weight to consider the values of A,-2A 2 . These were 



for several cases, A, and A 3 being expressed in terms of the squares of the 



weights. It was at once noticed that in several cases these differences were 



s of the same number, in the neighbourhood of 360, e.g., Ca 1, Sr 3, Ba 8, 



