PROF. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 69 



been found by correcting to constant v, also in P 2 , P 3 ( oo) has been taken to be ^he 

 same as P! ( oo). 



Remarks on Table I. NaP. It will be seen that agreement is perfect in NaP. 

 This is the only series in which the first three lines (from which the constants are 

 determined) are known with great accuracy. It has not been thought necessary to 

 give the comparison with all WOOD'S measurements, but after m = 10 they are given 

 for every interval of 5. The deviations from WOOD show that his observational work 

 (apart from instrumental) have mean errors of about +'05 A.U., and if his instrument 

 constants are comparable with K.R.'s, the constant P(o) in the formula should be 

 about '10 higher. RITZ has two outside, one 1'3 times and the other more than twice 

 the amount allowable. 



NaS is not a first-class set of measurements. Nevertheless, there is good agreement 

 except for S (6). For S (2) PASCHEN'S estimate of possible error is 1. For this a very 

 slight alteration in the value of a, or an error of '01 in S (3) (possible error = '10), 

 would bring both mine and RITZ' values within limits of error. The deviation in 

 S (6), however, is serious. It has the appearance of being chiefly due to a measure- 

 ment error, for successive deviations, as m increases from 4 to 8, are 0, 0, +'42, '12, 

 '32, and RITZ' formula suggests the same. If the observations are looked at more 

 closely S (6) gives v = 15 '89 instead of 17'2. LIVEING and DEWAR, in their early 

 measurements of this doublet, say : " The lines 4543'9, 4540'2 in the Normal Solar 

 spectrum probably represent this pair." These give v = 17'94. L. and D.'s measure- 

 ments are, of course, not to be compared with those of the later observers, but 

 apparently their method of producing the light had advantages over those of K.R. 

 Their observations generally give wave-lengths less than those of K.R., but in this 

 case they are much less, pointing to a suspicion that instead of X = 4546 "03 one 

 nearer 4544'8 would be more correct. X = 4545'Gl is that demanded by the formula. 

 Although, therefore, this case is a serious one against both formulae, there are yet 

 indications that it may be closer to the real value than the observations show. 

 S(7.8) are from L. and D.'s observations. The reading for S (8) is given by them 

 for the middle of a narrow band which they have not seen divided. For this 

 n = 23015'49. I have taken the readings for the two lines to be 23015'47|-(17'2), 

 and RITZ' result is also compared with this. 



NaD. The observation errors for all the NaD series are large. The deviation 

 from constant v has been referred to already, especially the excessive v of D (G), 

 which renders the readings for this very doubtful. The constants have been deter- 

 mined from L.'s readings for D (2) and K.R.'s for D (3.4). There is some uncertainty 

 as to whether ju, for the D series should be a fraction or 1 + fraction. The results here 

 are calculated for the form 1+f, but in all cases for D lines in this table the order of 

 a line is taken to be the integral part of the denominator whether we use p. = f or 

 1+f. The doublet at m = 6 is outside the limits, and it ought to be if v is to be 

 constant, also the reading for D 2 (5), but both D 2 (5) and D 2 (6) can be brought within 



