328 On the Stark Effect of the 4686 Spectrum Line. 



generalized by Epstein *, who, employing Sir E. Rutherford's 

 modeli of the hydrogen atom, has obtained results for the 

 positions of the components of the H a , H^, H y , and ~B S lines 

 of the Balmer series in complete agreement with Stark's 

 experiments. 



The complete theory of the effect of an electric field on 

 the 4686 line, which on Bohr's theory is due to a helium 

 atom consisting of an electron revolving round a nucleus 

 charge 2e, has not yet been published, but the ratio of the 

 separation of its components to that of the Byline of hydrogen 

 can be readily deduced from Bohr's simple theory. If, in 

 equation (1), for H^ we put N = l, ?? 2 = 4, n 1 = 2 J and for the 

 4686 line N = 2, n 2 — 4, w 1 = 3, it is found that the ratio of 

 the separation of the outer components of the 4686 line to 

 that of H/3 is as 7 : 24. This ratio of the separations will 

 also be approximately true for wave-length. 



Since the experimental results obtained by us at present 

 are not complete, it is proposed to examine the question 

 further, either with a spectroscope of higher power or by 

 the application of stronger electric fields. 



The experiments were carried out by Lo Surdo's f method, 

 in which the spectrum of the dark space in a helium vacuum 

 tube excited by a steady voltage was photographed. The 

 voltage was obtained from a 2000-volt dynamo connected in 

 series with a battery of small cells giving about 3000 volts. 

 The spectrum was photographed by a direct-vision prism 

 instrument which gave a bright spectrum and had such a 

 dispersion that hum. on the photographic plate at X 4700 

 represented 10'8 A.U. Several photographs were taken, one 

 of which is reproduced in Plate V. During this exposure 

 the constant voltage on the tube was 4000 and the pressure 

 of the helium was 1*96 mm. 



The strong lines which appeared on the plate consisted of 

 the lines of the ordinary helium spectrum, the H^ line (4861), 

 the mercury line (4358*5), and the 4686 line, which has 

 practically the same intensity in the dark space as in the 

 portion of the discharge immediately above. The H^ line, 

 the second member (4472) of one of the diffuse series of 

 helium, and the second and third members of the other 

 diffuse series at X 4922 and X 4388 showed the well-known 

 effect of the electric field which has been studied in detail 

 by Stark, Lo Surdo, and Brunetti J. The maximum distance 



* Epstein, Phys. Zeit. xvii. pp. 148-150 (1916). 



t Lo Surdo, JEstratto da L ' Elettrotecnica Giornale ed Atti deVC Associ- 

 azione Elettrotecnica Italiana, Anno i. no. 25, Ottobre 5, 1914. 



I Brunetti, Rendiconti delta R. Accademia dei Lincei, xxiv. (1915), 



