Helium-Hydrogen Series Constants. 4{U 



by . -., .,. in each case. Paschen was able to record 

 " 4(»r — p-) 



these lines in some cases, as shown in Table II. It will 



be seen that the tendency to lower values in the higher 



terms has disappeared in the series p = 4. The results arc, 



not very consistent among themselves, but this is readily 



explained it' we assume that in some cases only the borderino 



satellites were observed. The errors are all on the same 



side of the determined Nn e . Paschen's estimates of possible 



error of: observation are also given v reduced to our scale. 



Turning now to the Hydrogen (Balmer) series, we have 



the formula 



N H ^-N E Jg + i) m = 3,4,... (3) 



Nh being RM/(M + //,). M mass of hydrogen nucleus. The 

 careful measurements of Curtis* and Paschen {loc. cit.) are 

 given in Table III. Unfortunately they exhibit a small 

 systematic drift — Curtis's values increasing relatively to 

 Paschen's roughly linearly in terms of wave-lengths. 

 The first line H a is easily resolved into a doublet, e. g. 

 by Paschen in the third-order spectrum 8\ = '124z A.U. 

 8v="2S { J cm. -1 . The second line has also been resolved. 

 In Sommerfeld's theory the series is a set of doublets I, II, 

 of constant wave-number difference II — 1 = "365 cm." 1 , the 

 stronger component I being towards the red, but both 

 components being bordered on the long-wave side by fainter 

 lines rapidly converging in the higher terms. Paschen's 

 measurements are for "centres of gravity " while Curtis 

 endeavoured to record the centres of the diffuse lines (they 

 were not resolved). Now for the fainter lines component II 

 would probably vanish first, and the diffuse mean of the 

 photographic plate would tend towards I — that is, longer 

 wave-lengths. This may partly explain the minute drift. 

 Again, Curtis nsed Burns's secondary iron lines, while 

 Paschen used a variety — Fabry and Buisson, Neon lines by 

 Meissner. &c. 



The values of hn 2 vj(in 2 — 4) for the two observers are 

 given under C. and P., and in each case we find that a 

 minimum seems to have been reached for Paschen at H r , 

 Curtis at He. Now the stock corrections to the Balmer 

 formula all have the property of steadily decreasing, i. e. 

 no maximum or minimum, as for example the relativity 

 correction oiven in the table. Such a correction could 



* Proc. Roy. See. vol. xc. (1914) and vol. xcvi. (1919). 



2 K2 



