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



451 



The F (2) line should he a strong one in the neighbourhood of 17000. There are 

 a number in this region. The lines in the following list are found to give a good 

 series and is doubtless one F series. In this case we possess the great advantage of 

 very accurate interferometer measure of the 1st, 3rd, and 4th lines in international 

 units. These are used to determine the formulae constants. The wave-lengths are 

 given as measured, the wave-numbers are all in Rowland units. 



NeF. 



Notes to Table. For the first line PRIEST gives X = 5852'4862, MKISSNER '4875, 

 and MEGGERS '488. These all give the same wave-number to the second decimal place. 

 The second is a weak line by WATSON not observed by BALY. BALY gives a line, 

 intensity 4, n = 24039'45 not observed by WATSON. We have here a concrete 

 observational example of the facility with which a normal F line of low order can 

 split up into displaced lines by .slightly different excitations. Tn this case the 

 mantissse difference in the sequents is 159 and 11(5= 1591, so that 24039 is 

 F (3) (-11(5). The third line is a strong line observed by both WATSON and BALY, 

 but the measure used is deduced from an interferentially measured line n = 28439 '80 1 

 by deducting the WATSON link separation 1429 '429 (both accurate). WATSON'S 

 measure is 27009'95. The line for m = 5 is by MEGGERS, but WATSON gives the 

 same n. The remainder of the series comes in one of the gaps referred to above in 

 which only L.D. have observed. They give lines which may serve for m = G, 7. Also 

 for m = 6 there appears a linked line at 29257'2 + e = 29454'2 (using the value of e 

 found below). The calculated wave-numbers for m = 8, 9, 10 are 30422'G, 30703'3, 

 30906'5. No lines are observed between 30203 and 30722. The last two have lines 

 by L.D. near them at 307227 9, 30922'39. 



The formula as found from m = 2, 4, 5 is 



= 31850'19 



-N/ 



m+ 794726- 



m 



The calculated value for F (l) is X = 12241 '97 in vacua. 



