DISTRIBUTION OF INTENSITY IN BROADENED SPECTRUM LINES. 
401 
the phenomena of broadening which result appear to be similar. In a previous 
investigation it has been pointed out by one of the authors that from a consideration 
of the general characteristics of the broadening it appears difficult to refer the 
phenomena to the movements of the luminous particles as a whole, but rather that 
effects more intimately connected with the problem of radiation must be concerned. 
A recent suggestion by Stark* as to the cause of the broadening appears to be in 
harmony with the experimental results at present available. 
(II.) The Stark Effect in Relation to the Broadening of Spectrum Lines. 
Stark! has found that when a luminous source is placed in a powerful electric 
field the radiations are resolved into components in a manner analogous to the Zeeman 
effect in a magnetic field. The separation of the components in an electric field 
appears to be related in some way to the atomic weight of the element, the greatest 
effect being observed in the case of the Balmer series of hydrogen, and the diffuse 
series of helium. The separation is of another order of magnitude to the corresponding 
° 
magnetic separation. Thus at X = 4000 A.U. the separation of the outer components 
o 
of a normal Zeeman triplet in a field of 30,000 Gauss is about 0'5 A.U., whilst for the 
hydrogen line H y in an electric field of 30,000 volts x cm. -1 , the outermost components 
o 
are separated by 13'0 A.U. Stark considers that the broadening of spectrum lines 
at high pressures and under powerful conditions of electrical excitation is intimately 
connected with the electrical resolution of the lines, being in fact due to the electric 
effect of neighbouring atoms on the luminous particle. The phenomena appear to be 
strictly analogous. Stark also points out that the electrical separation of the 
components increases with the term number in a series, just as the broadening also 
increases. The electrical separation is greatest for lines of diffuse series, which 
also undergo the greatest broadening. Further, lines in the spectra of helium and 
lithium which are unsymmetrically broadened are also unsymmetrically resolved in the 
electric field.J 
It is evident that in order to obtain further evidence it is necessary to determine 
experimentally the distribution of intensity in the broadened spectrum lines, since we 
may predict (on this view) from the separation and intensity of the components in an 
electric field, the distribution of intensity to be expected in the broadened spectrum 
lines. In a previous communication§ a method of investigating the distribution of 
intensity in broadened spectrum lines was described, and it was shown that the results 
*- ‘Elektrische Spectralanalyse Chemischer• Atome,’ 1914. See also ‘Ann. der Phys.,’No. 18, p. 193, 
1915, in which the latest results for the Balmer series of hydrogen are given. 
t Loc. cit. A valuable discussion of the subject has recently been published by Fulcher (‘ Astrophys. 
Journ.,’ 41, p. 359, 1915). 
\ Reference may be made to the recent work of A. J. Dempster, ‘ Ann. der Phys.,’ 47, p. 791, 1915, 
who has investigated the breadth of spectrum lines with the interferometer, a method which the writers 
consider to be unsuitable for reasons given below. 
§ ‘Roy. Soc. Proe.,’ A 92, p. 322 (1916). 
3 R 2 
