DR. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 355 



(2<T,)P(<), the mantissa of m = 8 being at the same time subject to the fall of 

 multiples of S which would scarcely stop at 14<J. In the table, however, the errors 

 are inserted on the supposition that the mantissa? remain constant. 



Cs. 



The mantissre appear to run down by equal intervals from m = 4 to 6, are equal for 

 6, 7, 8, then a large drop of alxmt US to the same value for 9, 10, and return to the 

 value at m = 8 for m = 11. The possible errors are so large that the regularity is 

 curious. It is possible that they might run down at equal intervals of 3(5, to the last 

 one for m = 10. Or, if there are very small observational errors, the drop for 9, 10 

 may be due to a lateral displacement, about ( + 7<J,) D ( oo). It should l)e noticed that 

 with Cs all the order differences but one are multiples of 3*,, or the group multiple. 



Cu. 



The two first doublets of CuD are strong. The third is much weaker than would 

 be expected. Moreover, it gives a separation between D n and D 21 of 252*14, whereas 

 it should be somewhat less than v = 248'28. This (X = 3688 '6) can therefore scarcely 

 be the normal chief line of this doublet. Now EDER and VALENTA give a spark line 

 at 368775 which gives a separation with D 2 , of 245'91, leaving a satellite separation 

 of 2 '37, which is within limits in fair order with the corresponding separations in the 

 two previous doublets, viz., 6'60 and 3'39. Moreover, the satellite separation of 2'37 

 gives a satellite difference of 1317 and 9S = 1315, so that the normal satellite 

 differences would run 22e?,, 27<5,, 36<$,. This, then, would seem to be the wanting 

 normal chief line, and it is then interesting to note that the line usually accepted as 

 D u (4) is a collateral of this. The denominator difference of the two is 2474 and 

 17* = 2484 (S = 146). Hence the K.R line 3688 is the collateral D,,(4)(-17J), and 

 apparently the small intensity is due to the usual decrease produced by a negative 

 lateral displacement. The modified table is taken on = '08. It is remarkable 

 how close the observed differences come to multiples, but little reliance must be 

 placed on deductions from them both on account of the large possible errors and the 

 smallness of <V 



Ag. ' / 



Unfortunately the D series in Silver is poorly developed only the first satellite 

 has been observed, and the three chief lines after the first have very large possible 

 observation errors. Nothing, therefore, can be learnt as to the march of the satellite 

 differences beyond the fact that the observed 2436 is very close to 23<S, = 2421. 

 In the modified table = '1, the differences are very close as is seen to multiples of 

 J,, but there can be no certainty with such large possible errors. 



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