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



taking SAUNDEBS' values, except for the last but one, where LENARD'S is taken, 

 SAUNDEBS' reading would give a difference about 2 '5 greater, or 3 '5. 



When we consider the remainder, considerable difficulty arises owing to the 

 number of ill-defined lines so close together. In some cases K.H. and S. give very 

 discordant readings for doublets, which yet are so close that they look as if the 

 measurements might refer to the same lines, whilst in other cases the same observers 

 agree much more closely. It is to be remembered that apparently the method of 

 illumination has a great deal to do with the development of some of these lines in 

 the spectra in fact, they appear to come from different sheaths of the flame or arc, as 

 if it were a question of temperature. The doublet at 5675 was observed by K.R., 

 and was the only observation of theirs which did not fit in with the ordinary series. 

 It is peculiar in being diffuse towards the violet. Diffuseness to the red is a general 

 peculiarity of the diffuse series. If we look for the seat of this diffuseness in the 

 formula, it would appear to lie in the VD part of the formula through diminishing 

 denominator. If a series were such that the VD came to the limit as, for instance, 

 in many of the new series the VD would be additive instead of subtractive, and 

 the change in the denominator would now produce a diminishing wave-length or 

 diffuseness towards the violet. RYDBERG'S tables show that this doublet 5675, the 

 doublet at 4976 K.H., and 4660 range near his formula. They give, if K.H.'s value 

 for the second is taken 



n 



= 24558-0 ( + z>) - N/(m + 89484 + T 1 x '2369) 2 (i/ = 147, 12'1), 

 m being respectively 3, 4, 5. 



On the contrary, if we take 7418 S., 5675 K.R., and 5100 LE., we get a series 

 including in addition 4820 LE., 4660 S. As LENARD'S readings were very rough, we 

 may take the first and the last. There results 



+ l-33977-m- 1 x-06153) 2 , 

 giving for obs. calc. : 



5'3 2'6 0, 



which is sufficiently good agreement. The lines 5100 and 4660, however, have been 

 observed by LENARD alone, and neither by S. or K.H. It does not look as if such 

 lines, if really Na, would come next to so marked a line as 5675 K.R. The allocation of 

 these lines to one series is therefore very doubtful. It is against the former that no 

 other lines come in (a preceding line should be about 8025, and not likely to have 

 been observed if existent) ; but, on the contrary, the nature of the lines is more 

 correspondent, and it should be noted that the limit is within the limits of error of 

 the LENARD series. If the apparent agreement is real, the limit would be very close 



