160 On the Secondary Spectrum of Hydrogen. 



The value of A was taken from theoretical papers by 

 Lord Rayleigh * and Schonrock f . Thus they obtained 

 M=l for the secondary line (approximately), but a much 

 smaller value — probably (*5) — for the H a -line. 



Since the second value is impossible, they concluded that 

 in both cases M — 1, the value of A for H a being considered 

 unreliable, because H a is a double line, and it is rather 

 difficult to determine its limit of interference. 



But it has been shown in a paper published in the 

 Physical Review J that the value of A is subject to fluc- 

 tuations depending upon the silvering of the mirrors, the 

 definition of visibility, and other causes. In the papers of 

 Lord Rayleigh and Schonrock the value of A is calculated 

 from two interfering beams only, while in the Fabry-Perot 

 apparatus we have to do with an infinite number of inter- 

 fering beams. Hence no absolute reliance can be placed 

 upon a theoretically deduced value of A. 



Since for a certain particular apparatus A has a definite 

 value, the best interpretation of Fabry and Buisson's results 

 seems to be the relative estimation of the masses of the 

 radiating centres in the two cases. We thus have 



K 72,000 1 . M 0M f ---..in 



M 50 000 ' ° r Ms = 2Ml (approximately); 



i. e., the mass of the radiating centre responsible for the 

 emission of a secondary line is twice the mass of tha radiating 

 centres emitting H a . In other words, according to the inter- 

 pretation given here, the experiments prove the contrary of 

 what is generally deduced from them — viz., if the H a -line is 

 emitted by an H atom, the secondary lines are emitted by the 

 H molecule. 



It is to be hoped that the problem may be again experi- 

 mentally attacked. 



On the theoretical side the difficult}' is not only mathe- 

 matical, but also physical. We have not as yet any mecha- 

 nical model before us visualizing in a satisfactory manner 

 the coupling of two Bohr atoms into an H-molecule. In the 

 Bohr-Debije model the individuality of the component atoms 

 is entirely lost§. This is a serious theoretical objection which 

 has not yet been overcome. 



Nicholson || has already calculated, on the basis of Bohr's 



* Lord Rayleigh, Phil. Mag-, vol. xxvii. (1889). 

 t Schonrock, Ann. d. Physik, vols. xx. & xxii. (1906). 

 \ Saha, Phys. Rev., Dec. 1917. 



§ Lenz, Ber. der Deutsche Physikalische Oesellschaft, pp. 632-648 

 (1919). 



|| Nicholson, Month. Not. Roy. A. S. vol. lxxix. (1919). 



