PROF. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 07 



also (G) is nearly so. We note that Li agrees with the other elements in making 

 P ( oo ) jt. VS (1), and it differs also in the same direction. 



The form of VD recalls at once the formula for the F sequences found in Cs and Tib. 

 In fact, a RYDBERG form would well serve it. To test this we can find the differences 

 in successive wave-numbers. They are entered in the table above with the other 

 elements, and an inspection leaves no doubt but that here we have the F type. VP is 

 clearly a D type, although we should have expected the p, to be somewhat smaller. 

 The third series is thus VD(l)-VF(m), and the first VS (l)-VD (ra). The usual 

 D series, however, gives n = VP(1) VD (m), and we ought to expect to find it. 

 Now, certain additional lines have been observed by K.H. and S., viz., G240'3 S., 

 4636-3 S., 4148-2 S., 3924 K.H. If they are the series in question their wave- 

 numbers ought to differ by the same amount from those of the corresponding lines in 

 the old P. The differences are 14904732'8, 14903'932, 14914-10 + 10, 1490515. 

 In finding these the means of K.H. and S. were used, except for the last, which S. 

 has not observed, but EXNER and HASHEK have. The permissible errors have been 

 taken twice the difference of the readings of each two observers. The difference is 

 close to 14904. Since the limit of the old P is 43482 '20, the limit of the present is 

 the difference or 28578 , the same as for the old S. and D. It should clearly be the 

 same. Hence the formula is 



28580-N/(i+-951609 + ?HT I x '007365), 



the ordinary D type. 



In all the other elements we have met with series of the F type with limit VD (2). 

 Now VD (2) (extrapolated from the formula) is 12557, and lines of the new series, if 

 existent, ought to have wave-numbers 28580 12557 = 16023 below those of the 

 old D. The wave-numbers calculated in this way would be 5699, 8169, 9511, 10321, 

 10859, subject to uncertainties of a few units owing to the want of exact knowledge 

 of VD (2). The first two lines clearly appear in PASCHEN'S list of new ultra-red lines 

 with wave-numbers 5695'95 and 8173*22, or XX1755T6 and 12232'4. 



There are two lines of PASCHEN'S 18697'0, 12782'2, whose difference of wave- 

 numbers is 2474-26. Table III. shows that they must have reference to the F sequence, 

 and must be of the form 



A-VF(3) and A-VF(4). 



The actual values of their wave-numbers give A = 12202 N/(2'9980) 2 . 

 Now the D of F(2) = 2'998148. 



Hence these two lines are VF(2)-VF(3) and VF(2)-VF(4). 

 There are no apparent signs of series of the positive type. If we apply the multiple 

 laws deduced in the foregoing we should get for the D of P 



m+ 1 + -074560- ' 16120 - -000040 (l-- 



m \ m 



VOL. ccx. A. o 



