On the Secondary Sped rum oj Hydrogen. lf>9 



The observations at Dartmouth suggest that each locality 

 may be subject to an "electromagnetic tide" approximating 

 in regularity to the sea tides. Whether hydrography obser- 

 vations of these would lead to any practical applications is 

 doubtful ; much would depend upon the decree of con- 

 sistency of the data. It is, however, conceivable that a ship 

 might utilize the phenomenon as a means of measuring her 

 drift during thick weather. 



XIV. Note on the Secondary Spectrum of Hydrogen. By 

 Megh Nad Sa.ha, D.Sc, Lecturer on Physics, University 

 College of Science, Calcutta*. 



IN recent vears the problem of the Secondary Spectrum f 

 of hydrogen has again come to the forefront, on account 

 of the interest which attaches to it with regard to Bohr's 

 theory of quantum emission of spectral lines. Theoretical 

 physicists are inclined to ascribe the Secondary Spectrum to 

 the molecule of hydrogen, the Primary Spectrum being due 

 to the atom. On the other hand, many experimental physicists 

 are by no means satisfied by the explanation offered, but 

 on the basis of the experiments of Fabry and Buisson ±, the 

 opinion is sometimes expressed that at least a part of the 

 secondary spectrum may be due to the H-atom. 



But a closer perusal of the above-mentioned works of 

 Fabry and Buisson shows that probably proper interpretation 

 has not been put on their experimental results. In their 

 experiments the mass of the radiating centres was calculated 

 from the limit of visibility of the line in question in the 

 Fabrv-Perot interferometer according to the formula 



t-vi 



where A = limit of visibility, M = weight of the radiating 

 centre in terms of the H-atom as unity, = absolute tem- 

 perature, A is a constant. 



Fabrv and Buisson found that for the red line H a =656o, 



- = 50,000, while for a secondary line (not mentioned) 



- =72,000. 

 X 



* Communicated by the Author. 



t For example, Merton, Proc. Roy. Soc. Loud. vol. xcvi. p. 382. 

 Lenz, Ber. d. Ph. Gesellschqft, pp. 632-643 (1919). 



X Fabry and Buisson. Journal de Physiqite, pp. 435- 145 (1912), 



